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. 




OK thanks @donsachs   and @lynn_olson        I missed that price when I looked at it the first time online. A significant point you made Don is the fact that it will "happily drive a 10K amp impedance"   I have a new Coda amp on order and the XLR input is exactly that! I sent some questions to Spacial Audio regarding deposits and time it will take to get one. I want to keep a tube preamp in the drive train. My old one was 25 years old! Thanks!

I fully defer to Don, who is part of the loop of the Spatial team, who manufacture the preamp and power amp. I’m more like the system architect, guiding the project in a certain direction, and I’m not as aware of the manufacturing and production side of things.

One benefit of the output transformer in the preamp is it does accurate phase spitting, even if there is a small gain mismatch in the 6SN7 tube. Other balanced designs tend to rely on feedback for output balancing ... the Raven is zero feedback, either global or local, so transformers do the balancing and unbalancing conversions.

The input transformers are bypassed for the special case of XLR (balanced) sources. For example, many DACs have XLR outputs, since many converters inside the DAC have balanced outputs. On the other hand, tube phono preamps are often single-ended, so have RCA outputs. The Raven caters to both, with a source selector on the remote control. The Khozmo volume control is fully balanced, and so is the 6SN7 that follows it.

I believe the preamp is $5500.  Search for spatial audio lab, find the site and look at the revelation series and preamp and you will find it.  On the preamp, it is fully balanced and transformer coupled to output.  Pin 1 is shield and grounded to chassis, pin 2 is XLR + phase and pin 3 is XLR - phase.  It will drive any power amp with XLR connections, and will happily drive a 10K amp input impedance.

To the best of my knowledge, the price of the preamp is $5000. Possibly less when purchased as a bundle with the power amps. The XLR output should be AES compliant, driving both phase equally.

I'm very much hoping their is a build thread for the Speakers to be designed.

This is an area I am progressing into, as I have recently on a few occasions heard Speakers that are a a bespoke design and are as a end sound, what I believe are a challenge to my ESL's.

My personal preference for a Speaker does seem to have changed and a curiosity is now taking hold.

Even the idea of modding owned Cabinet Speakers and attaching Internal Wiring to a Drivers Voice Coil as suggested by another Speaker Builder on here, has my curiosity and is intended to be experienced when advisories are offered.

@lynn_olson  - Is the Raven Preamp AES48 standard balanced? They don't have a price listed for it that I can find.

A local store builds and sells their own high end tube gear and their own horn-based speakers.  For most of their demonstrations of the better horn systems they use their 350B amplifier.  One day when the boss was away, two of the younger employees spent the afternoon swapping in speakers acquired in trade-ins to see how they sound.  While all the speaker sounded quite different, they all sounded amazingly good to these two.  They could not believe how good even Polk speakers sounded.  It then dawned on them that the amplifier mattered a lot.  One did not get that kind of "transformation" of the speaker with the likes of Conrad Johnson amps, for example.  That is not to say that the CJ isn't good, it is just that the 350B amp had a particular character to its sound and that character played well with a wide range of speakers.

I tend to find that tubes related to the 350B do sound nice with a wide range of gear.  I tend to like 6L6 and KT 66 tubes (similar to 350B).  I run a somewhat similar, albeit much less powerful tube, the 349 (in pushpull) and I like it a lot.

I got into the amp game after auditioning both the Audio Note Ongaku and the Reichert Silver 300B on speakers of my own design. I’ve been designing speakers since 1975, so I have a pretty good idea what goes in them and why they sound the way they do. Crossover design errors, diffraction artifacts, enclosure resonances, driver breakup, etc. are things I usually hear in a few seconds when I listen to commercial speakers. So I know speakers pretty well.

What surprised me was the Ongaku and Reichert revealed things about my speakers I did not know were there. And different things between the two: the Ongaku revealed "space between the notes" in a way I had never heard before, as well as extraordinary, almost uncanny spatial realism. The Reichert deepened the emotional response to the music in a way that was outside the audiophile experience and not anything to with coloration or tonal balance. It was just a feeling, even when I was listening objectively and trying to assess what I was hearing. It just snuck up on me with a powerful emotional response.

It’s one thing listening to a commercial speaker that’s off-the-shelf with unknown design goals, semi-custom drivers, and unknown crossover design, but quite another when the speaker is something you’ve taken from initial conception to successive versions to final prototype. You’ve pretty much heard everything it can do, and have already built 13 different crossover variations and auditioned it on eight different amplifiers. You know that speaker inside and out.

And yet my speakers had undiscovered sonic aspects that were NOT part of source impedance (damping factor) or audible amplifier coloration. Things I’d never heard before. What kind of "distortion" gives MORE resolution, or a deeper, more profound emotional response? That’s nuts. Nonlinearity is not our friend; it steals resolution and separates you from the music with a haze of coloration.

So what’s going on here? That’s when I started researching the history of vacuum tubes and started writing for different audio magazines. I don’t believe in copying or "cloning" the designs of others; not only is it dishonest, it reflects a lack of understanding on why a product sounds the way it does. You have to understand the "why" before you can go any further, and that took about five years before I came up with the Amity in 1997.

Amplifiers are not as neutral as we would like them to be, and an amplifier with measured distortion in the parts-per-million range is not necessarily neutral sounding. They all have a sound ... Class D, GanFET, bipolar transistor, pentode, triode, and direct-heated triode.

I agree that the amp plays a very big role in the sound, and perhaps, too little attention is paid to the amp.  Far too many pick their speakers first, and then think finding the suitable amount of power will be the primary task in picking an amp.

Yes, I've come to the conclusion that speakers and power amps are about 50/50 responsible for overall sonics. Based on measurements, you'd think that speakers are responsible for 90% of system coloration, but in practice, no. The amps have a big role, too.


You are sure right about that.  I have Don Sachs new preamp and his shoebox 300b monos and swapped out my Cube Audio Jazzon speakers for a pair of updated AR 2ax speakers and they sound extremely musical.  A great front end yields benefits no matter what speakers you have.  Rest assured, the Cubes will be back in my system shortly.  

Many audiophiles underrate the contribution of pre and power amplifier in sound systems.

In most cases an extraordinary amplifier with average speakers sounds better than an average amplifier with extraordinary speakers.

If Spatial is at the Seattle show this year, yes, I will be there. I had a lot of personal stuff that precluded my attendance at Dallas, but it sounds like the SWAF was great experience and a good time for all.

Don tells me there is a lot of serious tech in the new Q3 speaker, and of course Don and I have rolled in a lot of new tech into the preamp and power amp since the Seattle show.

I expect I’ll be working with Joseph Troy Crowe on completing the notorious "Beyond the Ariel" speaker project started many years ago on DIYaudio. This will be a non-Spatial project, just between me and Troy, but it will be open-source.

My work with Don and Spatial will continue ... in the short term, I need to write the product manuals. If there is demand for new electronic products, I will be part of that, but Spatial designs their speakers with their own design team in Salt Lake City.

I just returned from Dallas, and I have to tell you that our room was one of the top two or three in the show.  Danny Ritchie (GR Research) came by and told us our room was his pick for best sound of the show.  Sam Whitt, the speaker designer at Spatial, just completely nailed that new Q3 speaker.  It is superb....  Of course the preamp and amps driving it didn't hurt either:)


Spatial Audio at the Southwest Audio Festival, with the new Q3 dual 15" dipole speakers and the latest Revelation Series Raven preamp and Blackbird power amps. The pint-sized Mola Mola Tambaqui DAC is tucked behind the Raven preamp.

Still making small production changes to the Revelation Series power amps and preamps. The main B+ power supply choke (filter) is now from Monolith Transformers and is on top of the chassis, along with the output transformer and the power transformer.

Spatial Audio now has the preamp and power amp in production (scroll down about halfway). The power amps are now 18" wide, the same as the matching preamp.

The tube lineup is 6SN7 input (balanced), triode-connected KT88 drivers, and 300B output in a fully balanced zero-feedback circuit. Monolith custom-design power and output transformers. The VR shunt regulators are on the right side of chassis, along with the power supply circuits. The audio circuits are on the left side, isolated from the power supply by an under-chassis shield running from front to back.

Revelation Series

I finished my integrated 300B SET project with two external power supplies.

It took me about 40 hours to drill chassis (thank you for my friend who helped me do it) and to assembly all parts together.

The amplifier sounds from scratch batter than my previous DIY amplifiers which was disassembled for parts for the new project. And it should sound much better after break-in.

Thank you guys for helpful advices.

I did most of those things for the Seattle trip. I hadn’t flown in more than a decade, and I knew it would be Hell on Earth if I didn’t tick all the boxes. So, in the months preceding, I applied for TSA Pre-Check, Instant Bag Check using the QR code on the phone, Early Boarding (for a fee), Lounge Access (lounge was closed), and Extra Seating Room (because I’m 6’ 1").

Most of it worked perfectly. TSA Pre-Check was fast and efficient. Instant Bag Check, likewise. Early Boarding, same. Extra Seating Room, yup, and pre-checked into a window seat both ways. Check. All perfect and worth every penny.

But ... the *&$@# concourse in Denver Airport was miles long, and there are several of them, connected only by a standing-room-only subway. And United changed the gate THREE times, sending a text to my phone just after I hiked all the way to the end of a concourse A, only to find no flight to Seattle after getting there. So then the flight is changed to the end of Concourse B (walking all the way back, taking the jammed subway, and walking all the way to the end of ANOTHER concourse), and then it got changed a THIRD time, right back to the end of Concourse A.

It must have been at least two miles, and there is nowhere to sit on this trek. Hey, airports are supposed to be ADA compliant, and I’m a tired old geezer about to fall over. So I ask a porter, can I get a ride in one of those ride-alongs I see whizzing by. Nope, you have to reserve a seat at least a day ahead with the airline you are flying on. No ride for you!

So ... the airport is grossly out of compliance with ADA unless you reserve at least a day ahead. Too bad if you are a single mom with an exhausted toddler, disabled with a crutch, or just plain old, like me, You get to walk, and walk, and walk, and if you fall over, well, tough. That’s your problem.

Oh yes, and I got Covid when I came home, almost certainly in the Denver or Seattle airports, which are both jammed each way. And then Karna got it 36 hours later, from me. Fortunately, Paxlovid dispatched it in a couple of days.

So I learned two things: wear an N95 mask in the airport, jetway, and airplane, until the airplane A/C is turned on. There’s plenty of fresh air on the flight (especially if you’re flying on a nice breezy Boeing 737 Max).

Second, reserve a wheelchair (by Federal law, no extra charge) at each end of the journey. The walking distances in both Denver and Seattle airports are stupendous. I felt truly sorry for the disabled folks and single moms ... they were at the ragged edge of endurance, with nowhere to sit and pause for a moment. The absence of any seating in the concourse is a scandal, and frankly, a health hazard for some of us.

Aside from the concourse horror, things went fine otherwise. Flying is fine if you have early boarding and a roomy window seat. TSA Pre-Check is worth the $80 charge and the FBI background check. I lead a boring life, there’s not anything to find.

And the show itself was great, as I expected. Sure, it was possible I was exposed to Covid at the show, but I doubt it. The airports were the human zoo, with tens of thousands of stressed-out people shoving past each other.

I very much miss the Portland to Denver Amtrak train, which was wonderful. Book a sleeper compartment and watch the countryside roll by. That was a wonderful trip.

@lynn_olson After Seattle last year, I made sure that I got pre-checked from TSA. Something like that can make your life much more pleasant. 

Don and the Spatial team will be in Dallas, but I will be home here in Colorado. If Spatial goes to the Seattle show this year, I will be there along with Don.

I learned my lesson about flying last year. This time, I’ll fly First or Business Class, and will wear an N95 mask while I’m at the airport. The show, though, was a lot of fun, and it was really nice staying at the show hotel and taking a nap in my room when I needed a brief rest. Also great meeting you folks in person, and seeing (and hearing) what’s going on in the industry.

No, not that I know of.  Dallas, and then I think they are planning on going to Seattle again in early Sept.  You should write them to see if they are planning on going to the east somewhere.  You can contact them via their site.

Just a note that Spatial will be at the SW Audio Fest in Dallas, March 15-17.  They will have the final production versions of the Raven preamp and Blackbird mono 300b amps driving their speakers.   I will be there all day Friday and Saturday, and a bit on Sunday morning.  So if you are in the general vicinity and want to hear this gear please stop by!  We will have tons of music on a hard drive, and if internet Gods are willing we will have Tidal and Qobuz available to queue up requests.  



Maybe Peregrine. Something fast and powerful, which are the hallmarks of these designs.

@downtheline Actually, next up is a two stage amp with another lovely DHT in push pull for a whopping 3-4 watts at very low distortion.  Not a 300b so not for this thread!  You could hang a custom transformer off it for phones.  You would want a REALLY good custom little transformer for headphones.  Not some off the shelf average quality solution.  Anything worth doing is worth doing to excess.  It would work and drive darn near any cans you would want to plug in.  You could even have multiple windings and perhaps a switch or two output jacks.  One for 300-600 ohm cans and one for the planar crowd.   Maybe in a few months..  First we get the Blackbirds and Raven off the ground (pun intended).  We have just built the first ones in Utah and I expect sales in Feb.  Then I can focus on other projects....

Sounds like the next project for your collaboration is a headphone amp for a wide impedance range of headphones!

As an overview, the Raven is a 1-stage amplifier with a 4.5:1 step-down transformer, and is output-limited by what both sections of a 6SN7 can crank out. The Blackbird is a 3-stage amplifier with a 28.7:1 step-down transformer, and is output-limited by what a pair of 300B’s can crank out.

The ideal solution for planar headphones is a 2-stage amplifier. For example, in the xDuoo TA-10R headphone amp sitting right next to me, a 12AU7 followed by a pair of Class A emitter-followers for each channel. Simple and inexpensive. Or, small power amplifiers in the 2 to 5 watt range ... all transistor, hybrid, or all-tube. The all-tube solutions ideally use step-down (output) transformers to match the load to the capabilities of the output tube.

Vacuum tubes can swing lots (hundreds) of volts, but are current-limited by peak cathode emission, typically measured in tens of milliamps, not amps. Bipolar and MOSFET transistors, in contrast, can pass not just milliamperes, but several amps, which is why they can be direct-connected to low-impedance devices like 8-ohm speakers and 20-ohm headphones.

A quick note on transformers: the voltage/current transformation ratio is the same as the turns ratio, but the impedance ratio is the square of the turns ratio. For example, the output transformer of the Blackbird, and many other other push-pull amplifiers, has a primary impedance of 6600 ohms, and a secondary impedance of 8 ohms. 6600/8 = 825, and the square root of 825 is 28.7228, which is close to the physical turns ratio. In a well-designed transformer, total losses are less than 5%, so can be neglected for this calculation.

So the output transformer of the Blackbird multiplies the peak current of the 300B pair by 28.7 times, offering peak currents of several amps to the loudspeaker. Similarly, the output transformer of the Raven multiplies the peak current of the 6SN7 by 4.5 times, which is plenty for driving a cable, but not really enough for planar headphones which mimic loudspeakers in terms of current draw.

@downtheline  The Raven has a headphone jack, yes, but as Lynn noted, it will only drive the typical old style phones.  It will not drive planars.  Sounds great with my old Sennheisers and phones of that type with 300 ohm impedance.  

Most likely not. It can drive 600 ohm phones no problem, but definitely not 16 to 32 planar phones, which are pretty popular these days. They require small power amplifiers in the 2-watt range.

Just heard the first production Raven was completed, and the folks at Spatial Audio in Salt Lake City thought it was a big step up from the Raven preamp at the show. It uses a new Monolith power transformer, a newly designed input transformer, and VR-tube shunt regulators, in addition to the regulator used in the show preamp.

Like the show preamp and Don’s previous preamp, it uses a Khozmo volume control with a remote control that adjusts volume and balance, and selects inputs. Tube lineup is a pair of 6SN7’s (one for each channel in balanced mode), a pair of VR150 shunt regulators (one for each channel), and a pair of damper-diode rectifiers.

The Raven and Blackbird use standard RCA and XLR interfaces, so they can be used with other components, but they sound their best when used with each other.

I showed the pix of the Amity (1997) and Karna (2003) amplifiers to emphasize they were developed largely in isolation from the SET community. I found out the hard way that SET practice wasn’t always useful with this approach. Similarly, practice in the traditional push-pull pentode world isn’t always helpful.

Don’s build and design experience with the Valhalla and Kootenai has been very useful, showing me what worked, and what didn’t. So there are elements of the Amity, Karna, Valhalla, and Kootenai in the Blackbird.

Do they sound like SETs? No, they do not. Do they sound like traditional push-pull pentode amps with feedback? No, they do not. The signal flow and functionality is different. The closest similarity are to some unusual designs of the 1930’s, with the very latest 21st-Century transformers and power supplies.

The Blackbird is actually the result of a four-way collaboration ... between Don, myself, the transformer designer, and the power supply designer.

... Actually, sonically the statements and the Blackbirds have similar heritage, but the Blackbirds are much better.   The Monolith Magnetics iron is just sublime, plus the power supply is improved in several ways including the addition of the pair of VR tubes.  The result is the Blackbird kicks it up a notch from the Statements, which were sort of a final prototype before we just pulled out all the stops and made the cases larger on the Blackbird.  I just returned from Utah, where I taught the guys at Spatial the builds of both the amps and preamp.   There will be actual units for purchase in January.

If it doesn’t say "electrostatic shield" there’s no copper foil between windings. Medical-grade is even better, with primary and secondary on opposite sides of the core.

If you want full isolation, in the absence of these features, you need two transformers, one for HV, and another for LV. The name brand doesn’t change the shielding, or lack of it ... that requires copper foil isolation, which is a definite hassle for the transformer builder.

I should mention the heaters for the rectifiers do not need isolation. Only the heaters and filaments for audio tubes need isolation. If DC regulation is chosen, a higher secondary voltage than 6.3 volts is needed, since regulators need to throw away a few volts to operate. I should mention not all regulators are the same; you can do a lot better than generic 3-pin regulators.

Hi @lynn_olson ,

The Hashimoto PT-100F power transformer that I'm going to use for drivers/input B+ and  drivers/input filament. But I'm not sure if it has an electrostatic shielding between HV and LV sections.

I can see some strips between high and low voltage windings. But as far as I can see they are made from a kind of cardboard.

@alexberger The resistor value isn't critical. 50 to 100 Ohms works nicely. As long as both chassis (power supply and amplifier) are tied together and grounded by the power cord, its really not going to matter where that resistor actually is, since it will carry no current under normal circumstances.

Hi @lynn_olson @atmasphere

I’m going to use a separate power supply (PS) box for my amp project. It is too big and too heavy for one box. I don’t want a monobloc solution, because it is an integrated amplifier.

I have 2 GND. One is a power cord GND (1) and another one a circuit GND (2). GND1 will be connected to PS and main chassis, while GND2 will be connected to GND1 thought resistor.

1. What value of resistor is recommended?

2. In which box GND1 will be connected to GND2 through the resistor? In the PS or the main chassis?

Post removed 

And here’s the very first version, the 2-stage Amity amplifier, built on old Tektronix chassis by Matt Kamna in 1997:

Here’s a close-up of the 2003 Karna amplifier, showing one channel of the audio chassis, with the power supply chassis out of sight. These have been my personal amplifiers until I received a pair of Statements about eight months ago.

Note the aviation-grade Amphenol connector on the rear of the chassis. All connectors and cables are rated for 1.5 kilovolts, using transmitter-grade coax cables to carry the two separate B+ voltages to the audio chassis.

In case you are wondering what all these tubes are doing, the input tube is a 5687 (or 7119), the drivers are old-stock 45’s, the outputs are 300B’s, one pair of VR150’s are for the drivers, and a single VR150 is for the input tube. The single EL34 is a current source that feeds the VR tubes. The four blue-painted cylinders emerging from the chassis are General Electric industrial motor-run capacitors.

The Statements and Blackbirds are an update of this over-the-top project. I was doubtful the Karna could ever be manufactured until Don came along, with his lengthy experience making the Valhalla (KT66) and Kootenai (KT88) amplifiers. Not only is it more compact, the new Don Sachs power supplies are an order of magnitude better ... and they didn’t exist in 2003.

The Statements are the previous versions. I strongly urged Don to use a spacious layout, with all components on a single layer. Easier to build and signal-trace. Don ran with the suggestion and improved it by putting all the power supply components on the right side of the chassis, all the audio circuits on the left, with a shield between the two sections.

The wiring for the audio section, in particular, is really simple ... transformers, tube sockets, cathode resistors, and bypass caps. The wire lengths for each half of the circuit are symmetric, while cathode resistors, bypass caps and local grounds go to turret boards next to the tube sockets.

The bigger chassis also run cooler, as you might expect, since heat-emitting components are further apart, and the top plate is now 18" wide. The Blackbirds might look big, but they fit just fine on standard racks.

Sonically, the Statements and the Blackbirds are pretty close. They are all descendants of the original Karna amps, which date back to 2003. Unlike the Karna amps, the Statements and Blackbirds are on two chassis instead of four, which vastly simplifies grounding.

Here’s a picture of Gary Pimm (foreground) and Gary Dahl (background), taken in 2003. The Karna’s have the distinctive blue chassis, and the separate power supply chassis are behind the amplifiers. The AMT-1's are Gary Pimm's speakers.

Gary Pimm and Karna amplifiers

Wow. Those Blackbirds are stunning looking! They're just a wee bit larger than my Statement 300b amps from Don.

[How does one post photos here?]