300b lovers

I have been an owner of Don Sachs gear since he began, and he modified all my HK Citation gear before he came out with his own creations.  I bought a Willsenton 300b integrated amp and was smitten with the sound of it, inexpensive as it is.  Don told me that he was designing a 300b amp with the legendary Lynn Olson and lo and behold, I got one of his early pair of pre-production mono-blocks recently, driving Spatial Audio M5 Triode Masters.  

Now with a week on the amp, I am eager to say that these 300b amps are simply sensational, creating a sound that brings the musicians right into my listening room with a palpable presence.  They create the most open vidid presentation to the music -- they are neither warm nor cool, just uncannily true to the source of the music.  They replace his excellent Kootai KT88 which I was dubious about being bettered by anything, but these amps are just outstanding.  Don is nearing production of a successor to his highly regard DS2 preamp, which also will have a  unique circuitry to mate with his 300b monos via XLR connections.  Don explained the sonic benefits of this design and it went over my head, but clearly these designs are well though out.. my ears confirm it. 

I have been an audiophile for nearly 50 years having had a boatload of electronics during that time, but I personally have never heard such a realistic presentation to my music as I am hearing with these 300b monos in my system.  300b tubes lend themselves to realistic music reproduction as my Willsenton 300b integrated amps informed me, but Don's 300b amps are in a entirely different realm.  Of course, 300b amps favor efficient speakers so carefully component matching is paramount.

Don is working out a business arrangement to have his electronics built by an American audio firm so they will soon be more widely available to the public.  Don will be attending the Seattle Audio Show in June in the Spatial Audio room where the speakers will be driven by his 300b monos and his preamp, with digital conversion with the outstanding Lampizator Pacific tube DAC.  I will be there to hear what I expect to be an outstanding sonic presentation.  

To allay any questions about the cost of Don's 300b mono, I do not have an answer. 




I now have a VC, which comprises of two matched Stepped Att' VC's for the mono block Pre-Amp' Design .

These are produced by a friend of mine specially for my Pre-Amp's Design only.

The usual ones produced are for my friends Buffer Pre' Design, I was requiring ones that are with a different measurement at 50K.

The Pre' Builder has expressed his satisfaction with them, and has heard them compared to a very similar Pre-Amp' design that has the other VC I referred to. 

FWIW, I drove up from Portland and met three friends to attend the show. There were three or four rooms that stood out, although our short lists were not identical. However, all four of us picked the Spatial Audio/Don Sachs room as our favorite. End game for all of us. I’ll leave descriptive words to others, but it was simply wonderful. It was crowded in there, but I had no problem getting in twice and listening to a couple songs each time. Great to meet Don in person after owning his pre and amp for several years.


We are among the fortunate to have Don's gear and I certainly share your opinion of the the room.  We both got to meet Don in person for the first time and he is a great guy, for sure.  Same with Lynn Olson.  Now with a month of run in with the new 300b monos in my system with my Cube Audio Jazzon speakers, every day of listening brings new joys to my ears.  

I got a little side tracked with this thread, I'm back into the 300b theme .

I did not share, that on Sunday 25-06, I was able to attend a demo' of a 'new to me' system, which has Klipsch Jubilees as the resident speaker.

The resident system in use was quite special.

Following the Lunch recess, a friends P-P 300b Power Amp' was put to use.

The 300b is a late 90's model of which Tim De Paravicini has an input to the design. This Amp is now overhauled and a few circuit tweaks are carried out.

The system owners reaction to this Amp' was immediate, the Cheshire Cat Grin lasted for many tracks.

All attendees were thoroughly impressed by the way this Amp' interfaced in this system and it really shone out for its attractive traits.

That is not the whole story, the systems pre-amp was swapped out for a Bread Board mounted, part completed pre-amp build.

This addition of the New Pre-Amp had a substantial impact in conjunction with the 300b. 

My take is that the design of the 300b in this Thread, has another 25ish Years (50 Years Combined) of experiences of Two Amp Designers, put to use, to help create this latest design.

I would get great pleasure from receiving a demo' of these mono's, to see where there are sonic traits that stand out as being more of a attraction and very much wanted to be kept.   

I’ve been a little quiet since I got whacked by Covid on my return to Colorado. Got an intense sore throat on Tuesday, tested positive on Wednesday, and started Paxlovid that afternoon. Doing better today ... actually, mostly better, and my mind is finally clear again. The metallic taste Paxlovid is famous for hasn’t been too bad, and it is fast-acting. (I tick three of the boxes for "high risk", so Kaiser Permanente of Colorado prescribed it right away.)

Strongly suspect the Denver or Seattle airports as the culprits. Total zoo in both places. If I go next year, I will ask for airline assistance getting to and from the gates. Two things that did work well were TSA Pre-check and Express Bag Check-In.

Don continues to evolve the Blackbird. Full-size chassis, some excellent parts choices, and bringing elements of the much-loved Raven to the Blackbird. The people on the Spatial Audio pre-order list are going to like them ... a lot.

Lynn, I hope you bounce back soon from Covid.  I got Covid in the remote state of South Dakota last year so go figure.  Your meds will  surely alleviate the symptoms.

Pindac, I heard the Jubilees in a local dealer's room and they are truly sublime, really stunning, fit for a way big room.  

I visited with the owner of Whammerdyne Audio who had his 2A3 SET amp driving the stellar Songer speakers.  As far as I can tell, the Whammerdyne designer has a different amp design philosophy than Don and Lynn, who favor a P-P design. Both Don and Lynn loved the sound of the Whammerdyne/Songer room at the Seattle show so that might say that there a lot of paths to get tube amps performing in an excellent fashion. I would have liked to hear those exemplary Songer speakers with Don and Lynn's 300b monos.  Yes I would and I bet Don and Lynn would too. 

I had a couple of flea watt tube amps including an excellent 8wpc Dennis Had amp that just ran out of gas even with my easy-to-drive Spatial Audio speakers.  Don and Lynn's 300b monos have ~27 wpc, which can drive a boatload of speakers.  Their mono's drive both my Spatials and Cube Audio speakers with alacrity, no question, no limitations.  And with dead silence between songs, more so than some of my excellent SS amps.  

Matt Kamna, the designer of the Whammerdyne, is an old Tektronix guy I’ve known since the late Eighties. We were at the second meeting of the Oregon Triode Society, and were both so impressed by what we heard at the meeting we set aside a project on a transistor amp .... for the simple reason it is much easier to get good sound than with transistors. Tubes are simple to work with and sound great, right out of the box.

Back in 1996, when I lived in Portland, Matt physically built the first Amity amp, although it was 100% my design from the ground up, and my first amplifier project. At the time, Matt went down the path of gigantic and extremely rare Western Electric power tubes in the transmitter class, I moved to Washington State, and then to Colorado.

Matt approached me a few years back and wanted me to write the user manual for the Whammerdyne 2A3 amp. He had definitely moved in a new direction. Matt’s an old friend and I didn’t mind some spare change, so yes, I agreed. The Whammerdyne 2A3 has some interesting user setup settings, and I had fun coming up with various names for the internal features of the Whammerdyne. Yes, I know what’s inside, in order to write the fairly complex user manual. (NDA’s were signed, etc.)

Internally, the Whammerdyne 2A3 couldn’t be more different than the Amity, Karna, Raven, and Blackbird (which are all closely related). Matt’s design is almost the anti-Blackbird, but what can I say, it works really well. I know from personal experience these things don’t design themselves. They look simple, but I can tell you, they are tricky to get right.

It was delightful to hear the latest Whammerdyne at the 2023 PAF. It physically looks more or less like the original, but sounds much more refined and elegant. It’s clear they’ve been working on it, and good for them for doing it. And it works really well with the Songer Audio speaker, another Portland company.

It’s interesting the SET folks are all-in on the single-ended concept, and have been since the early days of Sound Practices magazine. I certainly fell in love with direct-heated tubes, but felt from the beginning that the colorations of push-pull amps (compared to SETs) could be solved with a little creative thinking, and a return to the well of Western Electric research. I credit Vacuum Tube Valley and John Atwood for pointing me in the right direction.

Since I’m on a roll (and thankfully nearly out of the woods on Covid), let’s talk about PP coloration. It exists, it is real, and if you spend time with top-quality (not junk) SET amps, the absence of that coloration is wonderful and refreshing. Compared to Golden Age amps, everything is so clear, so open, so natural with wonderful tone colors. (Again, you never hear this with junk SET amps, which are murky and dark.)

The magazine conventional wisdom would tell you that clarity and beauty is "euphonic coloration". That’s complete horse****. Euphonic colorations can’t add detail, resolution, more depth, and more in-the-room presence ... colorations can twiddle with subjective tonal balance, and usually adds mush, murk, or grain. They don’t remove it. Build your own amps and you find this out right away (I can see Don nodding his head). The magazines have had this wrong for forty years.

Back to PP coloration. The mainstream "alternative" view is that it is inherent to to all PP, so just build SET and forget about it. Entirely aside from power considerations, SET has its own universe of colorations unique to SET, and they can be quite severe. What I call "junk" SETs sound like old antique equipment. So designing a really good SET isn’t quite as simple as it appears at first glance. At the top of the performance spectrum, it gets fiendishly difficult, with costs and complexity reaching into the stratosphere, and all charm and simplicity lost.

I’m in the small minority that feels the colorations of PP are very real and not imaginary, but can be solved. The Golden Age amps of the Fifties and Sixties, and the modern copies from the big name vendors, all have remarkably similar circuits, boiling down to three types (Williamson, Mullard, and Dynaco, with a handful of variants). These were adopted because they were well understood, responded well to feedback, and were cost effective at the time. Even Marantz and McIntosh were part of the watts-per-dollar race, which only ended when the Crown DC300 and Phase Linear 700 came on the market, putting all tube amps in the shade. From then on, if you wanted Big Watts, you got a transistor amp. Still true today.

But Golden Age is not the only way to build a tube amp. There were other, pre-war circuits, before the Williamson wiped out everything in 1948. The pre-war "floating paraphase" phase inverter ... not as perfectly balanced as later circuits, but more powerful. Transformer coupling, which passively inverts phase, but demands ultra-performance transformers, and also rules out global feedback. And other methods.

The prewar era had a lot of interesting byways and interesting circuits, which all disappeared by the 1950’s. And they do sound different, and get away from the 1950’s monoculture which dominates tube audio. The tubes don’t care; they cheerfully work in any circuit, provided you pay attention to operating point, loading, and stability (part of any amp design).

At any rate, when you stop using Golden Age circuits, the "PP sound" changes. It’s no longer a thick blanket that lays on the sound. It might be a brand-new coloration, or might go away. That’s where the fun starts.

@lynn_olson Another nice to read recollection of a History of Amp Design and the connections made over the years 'pardon the pun'.

Some of the content once more Jogs my Memory.

I recollect my 845 Power Amp designer/Builder, requesting that I keep him in the loop if any EE support is required during ownership.

Again as a recollection, it was made known there was their own Hooks in the Circuit Design, that was beneficial to creating the perception the sound produced was transparent.

I am now wondering if this was a similar description to your own, where creative thinking has been used to produce circuits with the potential to align the SET - P-P sonic where there is seemingly a mimic, rather than a contrast.

I am due to spend time with the EE, in the not too distant future, My Balanced Pre-Amp will soon be complete. Which will then be passed onto the EE, who is to work on the 845 mono's, whare a Balanced Design is to be produced, with the Single Ended option retained.

I have been a friend and loyal to this EE's Services for more than 30 Years, I think that has proved sufficient as a 'NDA' about his early works. 

As an aside, a few individuals have asked to see inside the Power Amp. One  individual wanting to make a mark in the audio world, who I knew quite well, and have not at present not communicated with for quite some time, attempted on more that one occasion to be allowed to take the Power Amps Base off and see the Circuit.

My not being supportive, at one time lead to my being threatened that I was on my own with any future EE concerns, if l did not accommodate the request. For other reasons relating to this individual, I am on my own 'Hey Ho'. I'm pleased I 'stuck to my guns' and honoured the Designer /Builders request , and I certainly am not on my own where EE support is needed.

Lets hope owners of your New Amp design, do not find themselves meeting Pirates scheming to steal another's IP.       


There are only a few things one can do to keep someone from pirating a design.   Point to point wiring and manufacture avoids circuit boards.  When someone sends a PCB design for manufacturing, there have been cases when designs have been stolen.  That said, there is little that can be done to eliminate someone tracing out the circuit.  I used to restore vintage tube gear years ago and one major American manufacturer would actually use regulator and other chips whose labels had been erased so you couldn't tell what part they used.  They guarded the schematics of course, so you simply could not repair their gear unless the problem was obvious.  

One just has to hope that owners are honest.  I have never had a problem with the issue.  I suppose should this design become wildly successful, someone may wish to steal it.  The power supply is non-standard and would be a little more difficult to copy, but the possibility exists.  So be it.

I might add that these preamps and amps will be produced by Spatial Audio Lab in Salt Lake City, UT.  The builders are young and will be around for a long time.  Should they ever need repair it will be easy shipping.  They should be quite reliable though.

When time served EE's who have leaned toward and made Valves a Circuitry, they have dedicated themselves to, there is a lot on offer under the hood, that should be very reasuring.

As for reliability, my Amp's have been on the Oscilloscope for numerous Hours/Weeks prior to them being released to me.

Never have the Amp's in all the time of ownership needed to be returned to the Designer/Builder EE due to any change in their performance from general usage.

I do have a Balance Pot' that I have damaged during Transit coming home from a public attended event I exhibited at, they were incorporated to assist with correcting Psycho Acoustics.

This will be checked out when the EE, has the Amp's for the circuit change, where a Balanced configuration is to be added.

I am thinking these Pot's could now be removed?, as the Mono Pre-Amp's, which are my end game keepers, are each with a VC.    

Dear Lynn,
Thank you for convincing me to use an interstage transformer for driving 300B in my SET. I installed Hashimoto A305 into my amp. I put 82K Ohm Kiwame load resistors.. First I measured the 6f6 driver stage with an oscilloscope. There is no overshoot on a square wave. (Thanks to Ralph for noting how to check the correct load that prevents transformer ringing). The frequency response -3db on small signals is 6Hz to 95KHz. The driver stage gives 150v peak to peak without visible distortion (with 300B working point Vg -65v). The output stage now has almost symmetrical clipping (and it was very asymmetrical with RC driver coupling). As a result, maximal power is significantly bigger than before.
Most importantly, the sound quality jumped to a different level. Much more transparent, higher resolution, bigger soundstage, more air and separation between instruments and together with its sound is less harsh, less grained. Even my DAC Chord Qutest sounds much more "analogue".

@alexberger Fantastic!  I love success stories!   I came around to really good ITs on this project.  LC coupling was next best, but once I got the custom wound Cinemag IT, designed specifically for the circuit it was no contest.  Enjoy your amp.   You have installed a top shelf IT and now you know why:)  There is no going back to coupling caps.....

Dear Don,

I'm also going to make an independent power supply for the driver and input stages. Now I use one 5u4g rectifier for both channel tubes 2x 300B 2x 6f6 2x 6sn7. The total current is 180mA. Is to much for one 5u4g. Now I have very big B+ capacitors, 2200uF for each 300B and 900uF for each 6f6 and 6sn7. But the independent power supply for the driver gave me better PS separation between output and driver plus gave me the option to increase driver tube current and decrease load on the rectifier tube.
I think I will continue to use the same 5u4g rectifier for 2x 300b and SS rectifier for driver and input tubes. Can you give me any advice, what is important to do for driver + input power supply?
I am also going to use the Lundahl plate choke LL1667 for 6sn7 input tubes instead of resistor load.


Electronics Engineer (EE)

Volume Control (VC)

For me and the amount of Typo's I keep making, it would be great if I could abbreviate a lot more words.     

Once you hear the difference an IT makes, you realize: "Aha! So that’s what RC coupling sounds like!" And then you start hearing that coloration everywhere in mainstream audio equipment, and can never forget what it sounds like.

This is an experience no reviewer ever has, even if they have $250,000 systems. Because why would they? Everything has been handed to them on a platter. They don’t know what’s inside the pretty box... it could be elves doing magic tricks for all they know.

What drives this exploration is curiosity. What will this sound like? Well, you don’t know until you try, and why take somebody else’s word for it? That’s no fun.

Grounding in the physics of tube function helps, because you get a feel what the device "wants to do". Pilots have a saying, "the airplane wants to fly". If you’ve ever been at the controls of an airplane as it lifts off the runway, you feel it. The vibration stops, the wings lift, the ground falls away, and you keep moving forward, a creature of the air, not the ground. You are now in a different realm.

Tubes are the same. They want to amplify. It’s what they’re made for. Our job is to get out of the way and let them do that, so we get into load-lines, the most linear region, what happens as the current dips downward, staying away from trouble spots, etc.

I made a little post a few days ago on Facebook, quoting a meme from my Ukrainian friend, Misho Myronov. When asked what his amplifiers amplify, he replied: "Happiness! My amplifiers amplify happiness!"

All of us who create tube amps get this. We do it because it makes us, and our friends who listen to them, happy. In the comments to Misho’s post, I added:

"I was just talking to Karna, and said, an amplifier is like a dance partner for the speaker. If the partner is dull and disengaged, the speaker will be bored and not interested. If the dance partner is lively and fun, the speaker will light up and come alive."

All of us who have solved a difficult technical problem, or just got a better amplifier, will hear the speaker really come alive and surprise us. That’s the happiness.


not being an EE myself I may have this wrong, but isn’t IT a long established superior way of coupling? Nobu Shishido’s Wavac EC300b with its superb Tango transformers is a prime example of the technique, isn’t it?

@donsachs ​​​​@lynn_olson 

It was great to meet you both at PAF and thanks to each of you for taking time to talk to me. That was the main reason I went there (and yes, Lynn, the lines at SeaTac were awful flying out). My given name is Jonathan and I know you were talking to a lot of different folks up there so you might not remember me. Don, you gave me information about a cable company and a semi-affordable DAC that wasn't as expensive as the top LampizatOr tiers. 

I posted most of my thoughts of the Blackbird (I suggested to David Whitt that you might come up with different names due to Raven Audio's avian naming for their tube amps) in the Spatial Audio Circle at Audiocircle but I was impressed with everything in both Spatial rooms and I spent significant time listening to both the Blackbird/Raven combo and Cloud's updated Valhalla amp with the X4 Ultras and both were impressive. 

I thought the Songer speakers were impressive as well although there are so many components in a room that, if you are unfamiliar with the speakers/amps/cables etc it is hard to attribute something you really like to one thing.

Since this was my first audio show, I asked a guy in the Seattle HiFi/Modwright room how things work because it seems to me the speaker is like the lead singer in a band, getting most of the credit and the spotlight and not always deservedly. He told me that they try to get synergy and sell the equipment as a unit rather than just sell individual components and I thought that probably makes sense.

I also saw certain kinds of music being played in most rooms, usually female vocals with sparse arrangements in order to show off the dynamics and quiet background. Some rooms had the music playing too loud to really make any opinions about anything other than "it's hurting my ears."

One of the things I liked about the Spatial rooms is that they were willing to play any kind of music and not always modern/hi rez stuff and they played at what I would call reference volumes which Goldilocks would say was "just right."

Anyhow, because of both of your willingness to share time and experience there and here, I really had a worthwhile time and learned a bunch. Thanks.  

@antigrunge2 Yes, IT is known as an excellent way of coupling, but it is expensive for very good ITs, and also they take far more physical space than your typical coupling cap.  So most vintage tube amps use RC coupling due to cost and size considerations.   Bad ITs don't sound very good, they can oscillate, or have very poor frequency response.  Done correctly with top shelf ITs and with a plan for the layout, then IT coupling walks all over RC coupling.   Medium ground is LC coupling with a high quality anode choke and good capacitor.  Also, there are circuits and tubes that are very difficult loads for ITs, so it is process of using the right method for the right circuit.  It is not one size fits all....  But in the right spot, I prefer IT coupling....

IT coupling dates back to the 1920’s Atwater Kent and radios of that vintage. Like field coil loudspeakers, it is the oldest form of coupling of all. But transformers have always been labor-intensive and expensive (going right to the beginning of electronic amplification), so when coupling caps became practical in the late Twenties, ITs mostly went away, although Western Electric and high-end radio builders used them as late as the end of the Thirties.

What pretty much ended them in all applications was the universal use of global loop feedback, with the landmark Williamson of 1948. You can wrap feedback around one set of coupling caps and an output transformer, but two transformers are out of the question. So IT coupling was moribund until zero-feedback amps saw a comeback in the early Nineties.

In the mid-Twenties, the only signal source was AM radio. Electrical phono pickups were just coming on the market, and movie sound was brand-new and experimental. By the mid-Thirties, movie sound was universal, with a bandwidth topping out at 8 kHz. Electrical phonographs could reach 8 kHz, but users often used "scratch" filters to soften the sound of noisy shellac 78’s. AM radio reception could go higher, but people often used the narrowband setting to get rid of interfering whistles from adjacent stations. The only truly wideband source was the Armstrong "Yankee Network" of FM stations in the 42~50 MHz band, which was limited to a few stations in the Northeast. These were the only FM stations in the world, and could be received by the high-end radios of the day.

It was only in the postwar years that wideband (30 Hz ~ 15 kHz) sources became widespread, with LP records in 1948, pre-recorded tapes in the mid-Fifties, FM broadcasting in the postwar 88~108 MHz band, and 70mm movies with magnetic soundtracks in surround sound. By then, all amplifiers were medium to high feedback designs, and used RC coupling throughout.

Modern wideband transformers were in studio use from the early Fifties, and the triode designs of the early Nineties opened the market for more unusual products, such as interstage transformers. True, it’s a 1920’s technology, but they didn’t have modern bandwidths back then ... the recording technology was unforeseen and decades in the future. What we hear now, with our ultra-wide band, ultra-low distortion sources, is a brand new sound, running through new-tech devices.

I hope you don't mind me going a tangent, but delving into modern and old technologies and taking advantage of such knowledgeable folks sharing with an open mind I wanted to humbly ask what function does a preamp fulfill in the context of a single digital source (DAC) driving a good SET? 

Here's why I'm asking: time ago I got into DIY speakers and adopted software-based FIR crossovers and 4-way active stereo, driving amps directly from a multiway DAC. AMT tweeters are driven from a 45 Yamamoto SET (hopefully not considered "junk" here 😊, combo sounds great to me), mids by KT88, midbass and subs by class D. My system sounds better now than it did before with branded speakers with passive xo, but I do wonder if I'm missing something driving amps from a DAC...I did love my Lamm LL2 preamp but I decided to optimize for digital sound reproduction with multiway so a stereo preamp didn't fit anymore.

In the context of not needing more than a digital source, the DAC producing enough gain such that using a digital volume control works well, and gain matching among amps being already solved, what would the advantage of using an interface between DAC and amps? 

Thank you in advance!

@lewinskih01 I have experimented for years with tube preamps.   When I built the Raven preamp it was after I had sent the 300b monos down to Spatial Audio for the Seattle show.  Then I built the matching preamp.  They were able to run the mono amps directly from the tube output stage of the Lampizator Pacific DAC, and they had one with a volume control.  I wanted to test it so I took used my Pacific DAC (no volume control) and implemented digital volume control in ROON.  It worked fine and sounded good.  I built the Raven preamp and inserted it in the system between the DAC and my 300b amps and the improvement was obvious.   I have done this experiment before with other preamps and DACs and every time I have preferred the sound of my good custom tube preamps to a direct connection from a DAC to the amp.  I have built passive preamps with the Khozmo volume controls.  I always preferred the active tube preamp and it was never close.  That is just my experience and others will undoubtedly have different opinions, but I have experimented off and on for years and always preferred a very high quality active tube preamp in the system.  That said, I have never owned active crossovers, nor will I, nor have I ever bi or tri amped a system, nor will I.  So my experience is not really applicable to your case.  I prefer the simplest system with passive crossover and one amp per speaker.   My 2 cents and of course your mileage may vary:)  This is why I build high quality active tube preamps for people with fairly simple systems.  Just my preference.   


I don't use tube rectifiers in power amps, but I do use them in preamps.  In your amp, if you wish to keep the 5u4g, I would consider using it for the input and driver section and using good quality diodes to drive a separate power supply for the 300b.   I use only regulated supplies, and I have my way of doing it that I don't wish to get into here.  But, yes, it is a good idea to have separate supplies for the input/driver section and the power tube sections.  What sort of supplies is up to  you, but a DHT will echo your power supply AND your filament supply very clearly so make sure they are very good.  

Good luck!


Hi, Lewinskih01!

You bring up two different approaches to system building. One is taking full advantage of modern multichannel DAC chips (8-channel is a common default size) and letting DSP do the heavy lifting. Taking it a bit further, tuning each amp for its own driver, rather than using a AV multichannel amp of marginal quality.

It depends on subjective priorities. Does the speaker need DSP to reach its full potential, and is DAC coloration small change in the overall scheme of things? Can’t say I blame you. Speaker colorations are obvious and gross, and DSP is the most direct and powerful way to attack them.

I have friends who own Altec Duplex 604’s and they don’t like it when I tell them the only way to straighten a 604 Duplex out is DSP ... no physically realizable crossover can fully correct it. Otherwise, you learn to live with the coloration, as Lowther owners do.

DAC coloration ... hoo boy, let’s jump into that rabbit hole, shall we? I feel most audiophiles can barely hear DAC coloration for modern delta-sigma designs ... and measurements are essentially perfect, far exceeding the 44.1/16 Red Book PCM specification. If a modern AKM or ESS converter with a circuit board full of op-amps is perfect for you, you can save big money, and jump on the DSP train with confidence. Do not pass GO, collect your $200, and enter the wonderful world of DSP. Amps built to taste are entirely optional.

Only a few people can hear differences between modern converters, and if you can’t, don't feel bad, you are part of the vast majority of audiophiles. Just buy a $700 Topping or S.M.S.L. and explore DSP. It’s what headphone jocks do these days. No shame in it.

Differences between DACs are weird and extremely subtle, and frankly you have to train to yourself to hear them. I can’t honestly recommend audiophiles go down this rabbit hole. It’s extremely expensive to pursue and full of deliberately confusing technobabble from slick marketers. Maybe not as bad as cables, but still pretty bad. Trust nothing when it comes to DACs, no matter how famous the name, or how glowing the review,

I was shocked and disgusted I could hear what sounded like "big" differences between my antique Monarchy DAC, with its Burr-Brown PCM-63K converters, and the latest confection from the Berkeley DAC (which any Topping will take to the cleaners these days). I also have the exaSound DACs which are ESS based.

I find DAC chasing neither fun nor enjoyable. The best are insanely expensive, and they go obsolete really fast. I might love the $13,500 Mola Mola I heard in the Songer Audio room, but the Mola Mola won’t be worth as much three to five years from now. DACs should be thought of as consumables that depreciate the moment you buy them.

Amps and speakers ... ah, now that is good value. Buy or build a good tube amp (and that certainly includes the $5000 Valhalla from Spatial) and it holds its value indefinitely. Similarly for speakers. The good ones cost more because the parts themselves cost more, and it takes serious design work to make them perform.

Well, enough of the rant on DACs. Addressing the question in the post by lewinskyh01, what does a really good tube linestage bring to the table if the DAC can directly drive the power amps?

A sense of ease, dynamic impact, and sometimes more vivid tone colors. How? Partly better cable drive, partly signal conditioning, scraping off RFI and noise induced in the cables. On paper, op-amps can do an amazing job driving a cable, in practice, not so much. If the preamp passes a quality threshold, yes, it can improve the signal compared to a direct connection to a DAC. Found that out the hard way with first Amity amp.

The magazine conventional wisdom would tell you that clarity and beauty is "euphonic coloration". That’s complete horse****. Euphonic colorations can’t add detail, resolution, more depth, and more in-the-room presence ... colorations can twiddle with subjective tonal balance, and usually adds mush, murk, or grain.

@lynn_olson You might want to play around with this applet:


Select 'sine' and the little dots below the waveform are movable and represent harmonics.

It shows why euphonic colorations (which are only the 2nd and 3rd harmonics) can indeed add to (or subtract from) detail and 'dynamics' and alter your perception of depth and soundstage.

If you only play with the 2nd and 3rd harmonics, and also work with their phase, you see some interesting results. For example if the phase of the 3rd is out of phase with the fundamental, the waveform actually gets taller.

Harmonics define the sound of musical instruments. You can see from this little applet that distortion can bring out details of musical instruments or obscure them.


I appreciate your candid views about the efficacy of DACs at varying price points. I was in the Spatial room when you heaped praise on the Mola Mola dac in the Songer/Whammerdyne room, a far less expensive DAC than the Lampi DAC in your room.  I read an owner's report that a Topping DE90 SE DAC for $900 was, to his ears, pretty much the same as the sound of his DCS Bartok DAC that cost ~12X as much.  My audio pal with nice gear has been is a rabid needle-dropper and he bought this same $900 Topping DAC and now honestly admits that his fealty to only analogue music is over as what he hears with this modestly-price DAC is pretty much the same as he hearing with his $15K analogue rig.

DAC technology, top to bottom, is really fantastic these days.  One of the happiest days of my audio life was getting a SOTA Sapphire vacuum TT in the mid 80's and another very happy day was the day I sold the TT to a local guy a few years ago, no shipping required.  Once I got an Ayre QB-9 DAC in my system, it was game over for my TT rig.  

Love ’em or hate ’em, DACs have gone a long way in the last thirty years, and continue to evolve pretty quickly. The internals of the AKM and ESS converters run at 90 MHz, with stupendous processing power. It’s what makes 4K TV and digicams possible.

That kind of speed makes up for many sins, and lets the noise-shaping algorithms operate much, much better than earliest days of SACD and single-bit MASH converters running at 2.8 MHz. In a lot of ways, it makes the endless upsampling discussions on the forums moot, since the internals are upsampling everything to 90 MHz anyway. Might as well let the chip do it, rather than play games in Roon. (Although converting PCM to high-rate DSD forces the chip to use different algorithms, which will definitely sound different.)

It is a consciously retro decision to use antique Eighties-vintage Philips TDA1541A converters, or late-Nineties Burr-Brown PCM-63 or PCM-1704 converters. Those are true once-through flash converters, with no signal processing or noise-shaping involved. But the least significant bits are kind of marginal, since it took R2R to the limit of what can be done with laser trimming and ultra precise fabrication. Nowadays, speed and good algorithms are the answer.

Which leaves the current-to-voltage converter as the last domain of audio tweakery. Op-amps are way, way better than the 1979-vintage 5532/5534 from Philips/Signetics, but you still find these antiques in consumer DACs. That’s probably where tuning happens in modern DACs, since there is little left elsewhere in the design.

And if you want to "sweeten" things, do it in the power amp or speaker. Much easier to tweak. I think making records sound like ultra-quiet, ultra-precise digital, or making CDs smoothed-out and "analog", is taking away from the strengths of each medium. LPs sound like LPs, and PCM sounds like PCM.

PCM to DSD256 is fair game, though, so why not? It’s what my Marantz SA-KI SACD player does to incoming PCM (it has S/PDIF and Toslink inputs), and an interesting "alternate view" of PCM sources.

lynn_olson's avatar


74 posts


Well, enough of the rant on DACs. Addressing the question in the post by lewinskyh01, what does a really good tube linestage bring to the table if the DAC can directly drive the power amps?

A sense of ease, dynamic impact, and sometimes more vivid tone colors. How? Partly better cable drive, partly signal conditioning, scraping off RFI and noise induced in the cables. On paper, op-amps can do an amazing job driving a cable, in practice, not so much. If the preamp passes a quality threshold, yes, it can improve the signal compared to a direct connection to a DAC. Found that out the hard way with first Amity amp.

Great! Thank you for the answer. Would building such a device, passing said quality threshold, be super expensive? This device wouldn't need volume control nor the capability to handle multiple sources. Maybe the device increases gain by a given amount and then listening level gets adjusted down through software volume control.

I agree it's an endless rabbit hole going down into the audibility of DACs vs upstream network settings vs software. And bleeding edge DACs bleed out their value soon after their peak in fame. Yet some more professional-oriented devices (such as Merging Horus/Hapi, Prism Titan, Lynx Hilo) are worth the same today as they were 7-8 years ago (nominal prices are higher due to inflation, price of Cu, etc) and still are the company's reference product. I like to stay among these, which of course are the ones capable of doing 8-ways.

My gut feeling has been there is something else good preamps achieve, and your post helps put this into more specific words. I'm not aware of any commercially-available product that does this and I'm intrigued to explore and maybe DIY. The idea of introducing a tube-driven class A stage to achieve "better cable drive, partly signal conditioning, scraping off RFI and noise induced in the cables" is appealing. How would you recommend I learn about this?

The idea of introducing a tube-driven class A stage to achieve "better cable drive, partly signal conditioning, scraping off RFI and noise induced in the cables" is appealing. How would you recommend I learn about this?

@lewinskih01 You might want to study how balanced lines work. Properly done, balanced lines are the best cable drive available to audio. RFI and noise are rejected due to the low impedance aspect of balanced lines (in the old days the studio line inputs were 600 Ohms; these days its more like 1-2KOhms); weak signals induced in the cable are swamped by the low impedance. In addition the input that is being driven has a high Common Mode Rejection Ratio, which is to say that signals common to both the inverted and non-inverted inputs (such as noise and RFI) get rejection.

In a true balanced line system ground is ignored to eliminate ground loops. If using tubes this is usually done using an an output transformer which can float with respect to ground. Its also possible to direct couple using a Circlotron output, for which Atma-Sphere has several patents.

If you are supporting the balanced line standards (AES48 is one of the standards; the other is the low impedance aspect) these two methods are the only ways to do it.

@atmasphere - If the input of the next component is balanced and not referenced to ground (e.g. transformer coupled), I don't understand why it is necessary to decouple the output in the source component from any ground reference to achieve the full benefits of balanced connections. Can you please help me understand. Thanks.

if the input of the next component is balanced and not referenced to ground (e.g. transformer coupled), I don't understand why it is necessary to decouple the output in the source component from any ground reference to achieve the full benefits of balanced connections. Can you please help me understand. Thanks.

@jaytor Part of the issue driving interconnect cables is how the signal travels in the cable. When the shield is part of that connection, its more likely to pick up noise and the actual construction of the cable (what sort of insulation it uses and so on) becomes more critical. That shield is connected to chassis ground at the input of whatever is being driven- so now you also have the possibility of a ground loop too.

So when the source is referencing ground, such as a pair of single-ended outputs, one of which is out of phase with the other, you have a problem where the ground circuit return is active in the shield of the cable. Suddenly the dielectric in the cable is playing a role that it did not when the shield was only used for shielding with no signal on it.

It is precisely this problem which is why there are 'high end audio' balanced line cables now that might cost up to $1000/foot or more (put another way, most 'balanced outputs' on 'high end audio' equipment actually references ground as if the designers were not aware of the balanced line standard)! If the connection is done properly, you won't be hearing the sort of differences between cables that might convince someone (who might have a touch of audiophile nervousa) to spend that $1000/foot.

I'm saying that an inexpensive cable can sound just as good in every way.

The proof of this is the vast number of recordings that were made in exactly this way- proper balanced outputs and inputs. Its part of why you could have 150 feet or more of interconnect cable between a microphone and the input of the tape recorder in 1958, nearly 20 years before Robert Fulton showed off his first 'high end audio interconnect' cable, yet the resulting recording just gets better and better as you improve your system's ability to winnow more information out of that recording. That can only happen if the cables used to make that recording are absolutely transparent!

Put simply, you have to dot your 'i's and cross your 't's if you want this system to work properly.

But let's look a bit closer at that balanced source that references ground. It may well be rack mounted in a relay rack and through that rack its chassis is grounded to every other bit of equipment in the rack or maybe even in the studio. Some of that equipment might be on the input side or the output side. So a ground loop could easily be introduced! 

You might think that because you're not using a 7' tall steel relay rack at home that you won't have that problem, but keep in mind that the equipment is also grounded into the wall. That's where you get in trouble: you must be sure that ground is ignored with both inputs and outputs; that ground is only used for shielding in cables and never for any kind of signal ground! If you don't do this, the benefit of balanced operation is eroded. It was designed so that exotic cables aren't needed and grounding issues are eliminated.

Think about the advantage of having cables that sound as good as the best out there price no object, but not having to pay that price- for all the interconnects in your system, you might have only a few hundred dollars invested at the most, rather than $1000s or $10,000s. And they don't go out of date or any such thing...


... On paper, op-amps can do an amazing job driving a cable, in practice, not so much ...

That’s a quite confounding claim. What components using op-amps do you find objectionable?

There are many excellent differentially balanced components that use op amp circuits, including all of the ARC Ref series preamps and amplifiers. Many people consider that a better approach than transformer-coupled circuits.


Due to package heat-dissipation limitations, most op-amps operate in Class AB. Now, they have a stupendous amount of feedback, and it takes a difficult load to excite the AB transition, but it’s still there. Speed is the friend of op-amps, so the high slew rate versions (more than 20V/uSec) often sound cleaner and smoother than the slower versions.

It is difficult to build a discrete solid-state circuit with distortion specs that exceed an integrated circuit, but it can be done, and they are often seen in the pro recording studio world. These do operate in Class A, and that is always mentioned in the sales literature.

I'm a bit surprised that ARC uses op-amps in their "Reference" series. Why not just buy Topping or SMSL and get even better performance, or if you insist on made-in-America, Benchmark, who live up to their name in performance standards?

Why buy an high-end audiophile component, with audiophile pricing, made from off-the-shelf $5 parts. What's the point? I don't see the value proposition. Now, if there are a zillion discrete transistors, and it does 1000V/uSec and delivers 500mA mA into a 300 pF load, that's insane, but still in the realm of engineering possibility.

Tube gear costs a lot because transformers and vacuum tubes are inherently labor-intensive, and the parts are not inserted on circuit boards with pick-and-place machines. I'm one of those madmen who think zero-feedback circuits are interesting, and I like tubes. Nelson Pass is your man if you like zero-feedback JFET/bipolar transistor circuits.

If you are more sensible, read ASR reviews, ignore the comments section, ignore the single-dimension SINAD number, and look at the noise floor of the multitone IM distortion graphs. That is the true wideband IM distortion, and multitone is the most severe test of the entire circuit. The Shenzen group of manufacturers have some really good engineers, and it shows in the IM distortion measurement. From what I can see, Bruno Putzey and the Shenzen guys are at the top of the game, if specs are at top of the list. They also know how to "tune" a power supply to get a subjective result.

I guess the micro-rant above is about audiophile components where the case costs more than the parts in the audio circuit. It doesn’t make sense to have a $500 case housing $50 worth of parts (in the audio circuit), unless the look is the main reason to buy the product.

I didn’t mean to imply any connection between Bruno Putzey and the Shenzen group. Bruno works in Europe, and designs top-class DACs and Class D amplifiers, which are inherently complex and very hard to get right.

The Shenzen engineers have slowly but surely improved their game, and the Chinese have been quietly building complete OEM products for high-end European and American famous-name manufacturers. Many deluxe and high-end raw parts are built right there in China, so they don’t have to go far to design and build their own high-end components, Whether you love or hate ASR, they have uncovered some terrific Chinese products.

On the international scene, a lot of truly remarkable products are coming out of Eastern Europe these days. Some real talent there.

This is where my good friend Lynn and I disagree:)   I have heard my Lampi Pacific in the same system as the May (which Lynn doesn't favor).  I have heard various tube based DACs, the Schiit Yggy and a few others for SS, and the Pacific is in a different universe to my ear than any of the others.  I have not heard the Bruno Putzey DAC except briefly in the Songer/Whammerdyne room.  I liked the sound, but I need to hear things in a known system.  That DAC was over $10K though.  I will bet money that in a blindfold test I will prefer the Pacific or perhaps the expensive SS DAC over the $1000 Chinese dac du jour on ASR.   Of course the rest of the system has to be totally transparent for such differences to be heard.  My 2 cents and others will disagree.  Of course the law of diminishing returns kicks in very hard somewhere about $1000-2000.  The Pacific and others of that class live and breathe in a way that even the May cannot (to my ear).

Why buy an high-end audiophile component, with audiophile pricing, made from off-the-shelf $5 parts.


It might be because those parts work...

Tube gear costs a lot because transformers and vacuum tubes are inherently labor-intensive, and the parts are not inserted on circuit boards with pick-and-place machines. I’m one of those madmen who think zero-feedback circuits are interesting, and I like tubes. Nelson Pass is your man if you like zero-feedback JFET/bipolar transistor circuits.

If you are more sensible, read ASR reviews, ignore the comments section, ignore the single-dimension SINAD number, and look at the noise floor of the multitone IM distortion graphs. That is the true wideband IM distortion, and multitone is the most severe test of the entire circuit.

FWIW, we use surface mount parts in the module we designed for our class D amp. We assemble them to the board by hand (no machines). You use different tools for that- a different soldering station, and special reader’s glasses so you can see what you’re doing.

You missed one of the more vital measurements: distortion vs frequency. Why this is important is that it can show you if the amp is going to make more distortion (and audible, annoying distortion) than the specs would otherwise show.

Zero feedback amplifiers have a ruler flat line across the audio band in this regard. Beyond that the distortion spectra must allow the distortion to be innocuous. That’s why SETs sound they way they do.

When the amp has feedback, that’s when you can have troubles with distortion rising with frequency. This happens because the design, whether tube or solid state, has insufficient Gain Bandwidth Product (and also points to poor engineering; feedback is control theory, which is a field that is well understood elsewhere in the electronics industry). For those that do not know this term, GBP is the frequency where the gain of the circuit has fallen to a value of 1 (unity gain) and so is the highest frequency where a sine wave can be relatively undistorted. Obviously an amp with a gain of one is not useful- 25 to 30dB is more useful so a preamp can drive the amp in a conventional manner (SETs don’t need quite so much gain, but since they don’t usually use feedback they aren’t part of this discussion).

For example if the amp has a GBP of 1 MHz and we are looking for 30dB of gain (a gain of 1000) out of the design, you divide 1MHz by 1000 and you get 1KHz. That is the frequency where the feedback will fall off on a slope (starting at 6dB/octave, but as frequency is increased, falling off faster)- and the distortion will rise on a converse slope.

This is why a simple THD value can hide dirt under the carpet; the fact that distortion will be much higher at 7KHz than it is at 100Hz. Its why most solid state amps can play bass just fine, but sound bright and harsh- you’re getting more of the audible annoying kinds of distortion at higher frequencies than the specs otherwise show! This has been one of the bigger disconnects between the spec sheets and what we hear over the years and has given rise to the myth that there are things we can hear that we can’t measure and explains why amps that ’measure poorly’ can sound so good.

It is recently become possible to build solid state amps that have so much GBP (we have 20MHz in our class D) that the distortion vs frequency is a ruler flat line, just like in an SET (but of course, overall much lower distortion, so greater detail is audible since distortion can obscure detail); IOW the feedback employed in such amps is supported across the entire audio band. That is why its now possible to build solid state amps that sound for all the world like the best tube amps.

FWIW ASR does on occasion graph distortion vs frequency on their site, but its apparent to me that they don’t understand its significance: the line that exists between that graph and what the amp actually sounds like. If you have all the measurements you can know that!

#hot take, one of the least important measurements is THD. Humans are inherently bad at hearing harmonic distortion don’t take my word for it there’s many blind tests you can do online to see how much distortion it takes before you notice. it tends to be shocking how much distortion there is before you notice it (especially if it’s low order). I’ve always had trouble correlating all things I hear with measurements. Still can’t really find a measurement that tells me how black the background of a component is. It doesn’t seem to be noise floor. I’ve heard many amps that have an incredibly low noise floor that aren’t very black sounding, other amps that have quite a high noise floor and are very black sounding. Multi tone seems to loosely correlate with this but again I’ve heard components with incredibly low and linear multi tone that aren’t very black sounding (Insert class D here). 
As for rising THD versus frequency, I haven’t experienced a refinement of treble with linear THD across the spectrum. Properly designed SS has been overall terrific in the upper registries over the last 2 decades. Pass labs, benchmark, and purifi all have terrific top end and all of them have rising THD versus frequency. And all 3 of those amplifiers employee very different topologies. 

As for component cost I completely agree with Lynn. If a component is cheaper to build, why are you charging me so much?!? I have no issue if a designer thinks a cheaper part sounds superior then a more expensive implementation. But you better not charge me more for that 🤨. This is something I appreciate about Atma-sphere’s class D. Ralph fundamentally believes it sounds better than what he was putting out before but he didn’t go charge an arm and a leg for it because “it sounded better”. 

To me it’s clear most of us have a slight different preference to the sound we like. The thing that makes the Karna mkII (blackbird) so attractive to me is just how much you can change the sound depending on what tubes you roll into it. Other tube amps I’ve heard do not change nearly as much as the Karna mkII. It is spooky transparent to what’s around it. Don very much likes the Linlai WE300B, but to me they aren’t my sound a little to smoky jazz club vibe sounding. Roll something else in and it’s a completely different presentation. Last night I was rolling the 6v6s and it was shocking the difference. Rolling in the JJ’s it was that classic JJ snap and speed in the midrange with a completely unrefined top end 🤮. Definitely won’t be sticking with that tube. But anyway my point with the Karna mkII is I’m not constrained to what Don and Lynn thinks it should sound like. I get to choose what it sounds like and that’s my favorite thing about it. 



[QUOTE="Helom, post: 32394540, member: 71602"]I suppose if I was specifically seeking a lightweight class D amp then I would probably give the Atmasphere model a try. I suspect most class D manufacturers are more concerned with cost savings and size rather than sound quality.[/QUOTE]
A good number of them are trying to get them to perform and sound as good as is possible.
[QUOTE="Richard Austen, post: 32397198, member: 53502"]I think the mistake you're making here is that as mainly an engineer you are looking at this from an engineer's perspective in that SET will go away because it doesn't measure as well as class D (or in your opinion, SET doesn't sound as good). 
...Someone like me will come around to class D simply because I don't really care that much about the technology - I care about what I hear. Gear is not the point - Music reproduction is the point. I just see history illustrating whether it is audio, politics, automobiles, etc that the best doesn't always win.  Lastly, I think really good-sounding Class D will also need to come from one of the big boys like Yamaha/Denon/Marantz/Sony to generate a larger foothold.[/QUOTE]
I am saying that tube power is on borrowed time because you can get all the best of the tube sound without the downside, combined without the weaknesses (brightness and harshness) of traditional solid state. So I see your opening comment above as a red herring- its not my assumption nor what I said or think. Class D is already here big time and all the big players are on board. So its foothold is enormous.
[QUOTE="Helom, post: 32397328, member: 71602"]I have yet to encounter a class D amp that doesn’t sound “thin,” regardless of specified power, or whether it’s a hybrid or employs a linear PS. It’s weird.[/QUOTE]
The simple answer here is you've not heard them all. Class D amps vary in sound quite a lot, more than tube amps do. Many of them really did have troubles getting the bass right, because they really didn't understand that the power supply really does have to be robust. The idea that they can skimp on that because the idle current is so low got them in trouble.
[QUOTE="Ampexed, post: 32397584, member: 143818"]The problem is that SET sounds the way it does because of its technical imperfections. No class D amplifier designer is going to deliberately make an amplifier which intentionally distorts the signal to the extent that an SET does (the company I work for makes a whole line of class D amps from mid-high end to very high end). Class D can and does sound just fine, but it cannot sound 'just like an SET' because the two types of amps are playing by radically different playbooks. That difference in sound is going to appeal to people with different priorities.[/QUOTE]
SETs sound the way they do because of their distortion. We didn't make our amps to have the distortion of SETs and they don't. But- like SETs, the distortion our class Ds make is mostly the 2nd and 3rd harmonics, with enough amplitude (also like SETs) to mask the higher ordered harmonics. Where its different is that overall the distortion is way lower than any SET, so it sounds more transparent. But it does so without harshness or brightness of any sort- and very good bass. Also like an SET it has a very good first Watt. How it differs in another way from SETs is the higher ordered harmonics don't show up at slightly higher power levels to cause the amp to sound 'dynamic'; IOW it does not have distortion masquerading as 'dynamics' as all SETs do at higher power levels (anything about about -6dB of full power).
Once you know the 'dynamics' of SETs is really just distortion it kind of wrecks it. So our class D is a lot more satisfying in that regard.
[QUOTE="Helom, post: 32400289, member: 71602"]Unfortunately most class D doesn’t work that way. The topology seems to distill the sound to a thin/lean presentation regardless of what’s upstream. This is especially true at high playback levels where many class D amps just “fall apart” despite their claimed power output.
It’s most apparent with the IcePower and older Hypex modules. Seems it’s still true with at least some of the GaN Fet designs also. Seems it has something to do with how they perform when asked to drive a real dynamic load as opposed to a simulated load.
This statement is false. The real issue is one I pointed out just above: Class D power supplies must be really robust; if not, they will have troubles with bass and might sound dry. This is one area where many class D amp producers skimp out. Its not a problem with the technology as it is the intention of the producer- are they trying to make a buck or are they trying to make a nice amp? The two are vastly different!
[QUOTE="Ampexed, post: 32400846, member: 143818"]Low bass is actually the Achilles heel of class D. They cannot take sustained periods of supplying close to DC levels of current, which is why they are typically rolled off before they have to pass the infasonic region of bass. If they used large heatsinks that would be less of an issue, but then the size, weight and cost advantage of class D would largely go away.[/QUOTE]
This statement is also false. If the amp is designed properly they can sustain current no worries. For example, our amp is rated 200 Watts into 4 Ohms. You can drive it with a sine wave at any bass frequency into that impedance and the amp will sit there and do it all day long- as long as you want with no worries whatsoever. Heatsink design is critical but its not a size thing as best I can make out. Our heatsink is also the mounting method of our module and so isn't any larger than the module itself. Yet the amp has no problem making current up to the limit of the supply itself. So it makes bass as good as any amp I've heard. 
This isn't rocket science. What isn't understood well in high end audio is that its driven by intention rather than price. This means good sounding products can be inexpensive, but it also means that you can do what is needed to make a circuit work the way its supposed to. Again, in a class D, the most common sin I've seen amp producers do is they skimp on the power supply. That results in everything you said. But that's not a weakness of the tech, its a failing of the person that's trying to save a buck. It results in failure.  

As for rising THD versus frequency, I haven’t experienced a refinement of treble with linear THD across the spectrum. Properly designed SS has been overall terrific in the upper registries over the last 2 decades. Pass labs, benchmark, and purifi all have terrific top end and all of them have rising THD versus frequency.

@cloudsessions1 Just so you know, this statement is false. Most self-oscillating class D amps, such as the Purifi, do not have rising distortion with frequency. Where ever you got that your source is wrong.

Regarding this comment:

Humans are inherently bad at hearing harmonic distortion don’t take my word for it there’s many blind tests you can do online to see how much distortion it takes before you notice.

This test is probably not done with attention paid to distortion rising with frequency- and in that context your statement is correct. Most of the online stuff I've seen does not have that built-in to the software. So its not the same thing. When distortion rises with frequency, it puts emphasis on higher ordered harmonics. This is at the root of why solid state has had a reputation for being harsh and bright, and also why feedback has gotten a bad rap in high end audio (because it can mess with a tube amp in a similar fashion).

I've already described how Gain Bandwidth Product causes the rise in distortion with frequency. What I've not mentioned in this thread so far is how feedback is usually applied in amplifiers so that the feedback signal itself gets distorted before it can do its job mixing with the incoming audio signal. As a result higher ordered harmonics and intermodulations are created because the feedback node is not linear. Norman Crowhurst (a well known audio guru of the late 1950s and 1960s) wrote about this over 60 years ago, but almost nobody really did anything about it.

You can apply feedback without distorting it. That is done the way opamps do it, by mixing the feedback with the audio signal using a resistor network at the input of the amplifier, rather than inside the amplifier. Resistors are far more linear than any tube or transistor! We've employed that technique in our smaller OTLs for decades now.

@atmasphere you can see the purifi’s distortion vs frequency here: https://audioxpress.com/article/fresh-from-the-bench-a-tale-of-two-class-d-amplifiers-orchard-audio-bosc-and-purifi-audio-eigentakt-eval1 here: https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-purifi-1et400a-amplifier.7984/ and here: https://www.stereophile.com/content/nad-c-298-power-amplifier-measurements


Now the Purifi is a good sounding amp with excellent employed feedback. But it does not rival the best tube gear I’ve heard let alone my $5k Valhalla. 

As for THD+frequency. Agree to disagree. I have not heard any properly designed SS that isn’t good in the treble whether it has a rising distortion plot or not. to me that was a problem in the 80’s and 90’s. Designers have long known the impacts of high order distortion and taken steps to reduce it in the last two decades. The Pass labs XA60.8 has some of the best treble I’ve heard. It’s sweet, articulate and smooth and it’s distortion rises over 1/2 a percent at 20k. 

@cloudsessions1 Thanks for the links!

Given how much Bruno Putzeys has written about this topic it was my assumption that all of his designs conformed to his ideals. Assumptions can get you into trouble...

I'm Ok with the agree to disagree. I've met very few solid state amps that I could actually live with; hence 45+ years in business making tube amps. I do agree its less of a problem now as opposed to +20 years ago. The semiconductors needed to do the job really didn't exist in the 80s and early 90s.

The Karna Mk II/Blackbird is bit by bit evolving towards the original Karna, but without the madness of a four chassis design. Having a separate chokes and power transformers for #1 B+, #2 B+, and the filament supply gets really heavy and awkward. Don’s monoblock approach is much more sensible, and more important, he has real-world experience of what is reliable in the field.

I design things as a thought experiment, just to see how it works out. About one design in three is a flop, and gets abandoned. You have a sound in your mind, and wonder if the real thing will sound like you imagined. Sometimes it does, sometimes it doesn’t. You never know in advance.

The Raven and Blackbird were, and are, thought experiments to explore what minimum intrinsic distortion would sound like. Zero loop feedback, and zero local feedback, with all cathodes fully bypassed. Balanced, but not differential, with passive transformers doing the summations and cancellations.

It is not SET, which require skillful arrangement of various colorations and very, very careful component selection. But it still requires careful selection of components because there is no feedback to minimize and wash out colorations. If XYZ tube has a certain sound, well, that’s what you’ll hear. If XYZ cap is imposing a coloration on the cathode circuit (which is a very sensitive circuit node), yes, it will be audible.

A big difference between the solid-state world and vacuum tubes is capacitance. Capacitance with tubes is essentially linear, aside from Miller capacitance, and even then, the delta in the capacitance is very small (no more than a percent or so). The transit time through the circuit is constant, regardless of signal. Part of making the transit time constant is passive (not active) phase inversion and summation.

Solid-state capacitance is known for varying with current and temperature, so it pays in transistor circuits to get the (nonlinear) capacitance to the lowest value possible ... if it can’t be linearized, get it as close to zero as possible. Modern transistors are much faster than previous decades, so this really helps. Build a very linear video circuit, and many problems are solved.


Could you expand further on your balanced, but not differential comment? What is your philosophy, what have you observed?

I can appreciate the desire to chase the sound quality rabbit to fruition, but it seems likely this will result in more boxes and a bit higher cost. No doubt there is a market for this. Maybe there are two markets? Two versions at different price points?

A bit of background on cost to the consumer: if a company isn’t charging Bill of Materials (BOM) cost times four, they won’t be around very long, one or two years at most. This rule-of-thumb has been true since the Fifties (for hifi manufacturing in North America).

Not true for cars, of course, since that is a hyper-competitive, extremely price-sensitive industry that has enormous capital barriers to entry. In electronics, the Chinese are able to shave it down to two to one, most likely due to a wide range of hidden subsidies that favor exporting.

So a smart DIY’er can indeed get serious high end for medium (not low) cost, partly by pricing their labor at zero. But even a very experienced DIY’er is going to find that building a Blackbird from scratch is the same as the price of a good used car, setting aside labor and debugging time. I know several people who got stuck halfway through building a Karna and wanted many hours of my free help completing it. No, that’s not how it works. You want a Heathkit, go buy one. If you can design and build an amp from scratch, more power to you! Have fun! Be glad you don’t have to use a slide rule any more, like the bad old days.

(Yes, I have used slip-sticks. They are no fun. You’re lucky to get 2% precision, and you have to do the calculation twice because it can be off by a factor of 10 or 100.)

Back to circuits. A differential and balanced circuit are not the same. A differential circuit has a current source or high-value resistor in the common cathode (or emitter) circuit, which is why they are called "long-tailed pair" in the literature. This forces differential operation, but has a limitation because the two tubes (or transistors) are effectively in series. If one device cuts off (impedance goes to infinity), then the other device is hard-limited to 2X the quiescent current. It can never go further, because the long-tail or current source hard-limits total current to both devices.

By contrast, a balanced circuit, without a long-tail or current source, can turn on the "on" device as hard as it likes. That can be as high as 5X the quiescent current or even more. It effectively slides over into Class AB if it needs to, unlike a differential circuit, which will hard-clip if too much current is demanded. The phase splitting is done by transformers, not a long-tailed pair.


By the way, if you are looking for value, you really should audition the Valhalla from Spatial. It took on every other high-bucks big-name tube amp at the show and came out ahead, often by a good margin. It is a seriously good amplifier at an absurdly low price.

Now, if you are looking for 100 to 200 watts of tube power ... hate to break it to you, but paralleling arrays of power pentodes does NOT improve the sound. Rule of thumb for PP tube or transistor: no more than two devices if you care about quality. Once you start paralleling arrays, there’s always just a bit of mismatch to trip you up. And that’s just DC matching, which is completely separate from matching transfer curves (AC matching). That’s a lot harder, and there’s always the issue of tubes drifting apart as they age.

The other issue with arrays of pentodes is the grid capacitance for the power tubes is multiplied, which then requires high-current cathode followers, or separate power tubes as drivers. This gets into No Fun territory as the design complexity multiplies, all just to squeeze out a few more watts.

From my perspective as an amp designer (not as a consumer or reviewer), the Sweet Spot in tube amps is from 3 watts (Class A SET) to 60 watts (Class AB PP pentode). These are all simple circuits with an emphasis on sound quality and reliability.

If you MUST have 200 watts, consider combining a modern Class D amp with a preamp like the Raven. The new Class D amps don't have the irritating and fatiguing Class AB sound, while a good tube preamp lends the sound some charm and likability.

A differential circuit has a current source or high-value resistor in the common cathode (or emitter) circuit, which is why they are called "long-tailed pair" in the literature. This forces differential operation, but has a limitation because the two tubes (or transistors) are effectively in series. If one device cuts off (impedance goes to infinity), then the other device is hard-limited to 2X the quiescent current. It can never go further, because the long-tail or current source hard-limits total current to both devices.

This statement is false. The devices are not in series, else Kirchhoff's Law would prevent the second device from conducting if the first were in cutoff... At any rate if one device is in cutoff, the other will be in saturation which is the limit of any device's ability to conduct!