I am an importer for a company that produces wonderful SETs and my speakers that I make use Eton drivers.
In your price range, your best option for a power amp will be the Rogue Hydra but you will need to roll in different tubes. I would suggest hunting down some NOS Mullard Longplates. It is not going to sound like a SET but at least it will sound like a tube amp.
You should be able to fine a used Hydra in the $1500 to $2200 range depending on condition, private sale vs. used dealer, etc... I personally still own a Hydra and it is a very good sounding amp. New it will list for $3K.
Although I am a dealer, I have no affiliation with Rogue. |
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And despite the modest power rating, this amp had startling dynamics. Because the ear uses higher ordered harmonics to sense sound pressure, and because this amp was really being pushed to hard to drive this speaker, higher ordered harmonics were showing up on the transients where the power is. IOW, it was distortion masquerading as 'dynamics'. The mark of a good system is that it does not sound loud even when it is. This will be because distortion is controlled. SETs make a particular type of distortion known mathematically as a Quadratic Non-linearity. This results in the primary distortion component being the 2nd harmonic followed closely by the 3rd. This gives you a rich sound, but again its due to distortion. The only class D amps that make that kind of distortion are zero feedback designs. You'll have to ask if they have a quadratic non-linearity; if they don't know what you're talking about don't buy the amp even if you don't know what that is either :) Amps that make a 3rd harmonic might be interesting to you. The ear treats the 3rd the same as the 2nd, but amps that make the 3rd harmonic as the primary distortion component tend to be overall lower distortion. If you want the musicians to sound real this is a better way to go. Such an amp will still have some romance- it won't be dry. Have you considered other tube amplifiers? |
The best-sound class D right now (pending a few anticipated future releases) are likely going to be the AGD, already mentioned above, and the LKV Veros. Both of which are well outside your price range.
SS: along with Pass and Accuphase, I'd add Sugden. |
I just don't see you finding the magic you've had anywhere else but tubes. Asking to get that magic while also playing loud AND for under $3k is a pretty tall order. At least with your speakers, which if they are the clones you say they are then they are about 95dB. Which could be worse, but could also be better.
All I can say, I get plenty of tube magic from my Melody, (it was about $2500 full retail when new), and a Raven Nighthawk will sound even better and you can get one for $3k. The Melody was able to play good and loud with Talon Khorus that were only 92dB. Now with Moabs at 98dB it plays a lot louder without ever going anywhere near where it was with the less efficient Khorus.
Of course we have no way of knowing if your DIY speakers are 95dB, or more, or less. Huge difference. Could be all you need are Tekton Double Impacts.
Anyway, I would totally give the Raven Nighthawk a try.
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What I heard with the JAS Array 2.1 was a purity that I hadn't heard before nor in any thing else in my system since. The sound was not warm nor lush. It was quite neutral in that sense if not slightly lean. And the images had a fullness and a very clear place in space that sounded "real". It was just more detailed with subtleties that increased realism beyond anything else. That's what I'm asking about in a possible Class D replacement. I hear much of it in some of the gainclones I've tried but they tend to be lower powered as well. For 90% of my listening, that's not an issue. And I don't think I was pushing the JAS or the gainclones the majority of the time. But, there are those occasions and some music just cannot be listened too at lowish levels, right?
Atmasphere--you've responded to a few of my inquiries and I always appreciate your comments. I put on my reading glasses and go over your comments several times to make sure I comprehend all that I can. Regarding tubes.....I would be happy to try something like the Rogue Hydra. But I want to get away from a full-tube amplifier.
And I gave a lot of thought to the Pass xa 25 and 30.5. I posted here asking about their transparency/detail compared to the Gamut D100/200 and got the impression that they are a bit less detailed and perhaps colored. The reviews sound great but leave me wondering if there are options closer to what I'm looking for.
Millercarbon----I have read lots of Tekton reviews and have considered the DI SE's. Most reviews sound spot on for what I like in a speaker but every now-and-then, a reviewer comments on how the top end just doesn't sound as polished as it could. I read that the Spatial Audio M-4 bettered the Tektons. Now, I'd have to look it up the be more specific, and I did see other similar complaints but more than anything else, I really do like my DIY/Legacy Focus clones. They replaced a pair of Von Schweikert VR 4 gen II and the improvement was vast. And since then, I lined the cabinets with sound deadener, rewired with solid core silver plated copper and paid to have the crossovers upgraded. I also bypass the binding posts and run the wires directly to the crossovers. And they're just to damn big to ship.
others----will look into the Hydra, the 12au7 has been a long time favorite tube of mine. I will also look into the AGD and LKV amps. These are the kind of recommendations I am hoping for, amps I've never heard of. There are just so many fairly obscure Class D amps to investigate so thanks for pointing me in the right directions. Thanks all! |
@icherekpal,
You had a beautiful sounding amplifier, 300b driving 805 DHT output tubes. I don’t believe you’ll find a class D, SS or push pull tube amplifier that will match the "magic" (I appreciate your use of the term in this context) tactile realism and tone you miss from the JAS Array SET.
I do believe that you’ll find a very good sounding replacement amplifier that is overall a better match with you speakers. I get your point about replacement cost of the 300b and 805 tubes (Worth it in my opinion for the sound quality you received). If I were in your situation I'd keep the JAS and find more compatible speakers.
Best of luck,
Charles |
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The AGD seems to be a very nice alternative amplifier choice but is well outside the stated budget of 3000.00 USD.
Charles |
Buy a used ClassD that outputs at least 500 watts @ 8 Ohm. If it doesn't work for you resell it. I see a couple of good used ones on here and TMR. |
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Here are some more popular class D options,
PS Audio Stellar M700 are Stereophile Class-A rated .......
Bel Canto class-D mono-blocks, REF 600M
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djones51--- I was looking at the Nord monoblocks on TMR. Any experience with them? And I'll be looking for used LKV or AGD amps though it may be a while before they sell at my price point. Sucks to be poor! |
Charles----I already sold the JAS. I had it repaired a couple yrs ago, a problem with a bank of bridge rectifiers if I recall correctly. I used it briefly until the heat made me switch in the warm weather substitute amp. I then moved 3 times in 2 yrs and only recently attempted to install the JAS again. It didn't work correctly and the tech who did the work had retired with no one remotely close to pick up his spot. So..... I'll certainly miss that amp but I really don't want to mess a full tube amp again. I'm happy to try hybrids. Anyone use the Rogue Hydra or Medusa? |
No other than they are using good Hypex modules. I've heard the March 502 that also uses Hypex, very neutral amp with good power. |
I think the answer here could be quite simple. I have recently been researching tube amps for my Focus SE's and have come to the conclusion that there isn't a tube amp out there that can drive them properly. So think about it, Mr Dudleston makes several of his speaker models with powered low end drivers. Simply use a class D amp on the low end drivers to control the bass and then pick your favorite tube amp for the top end. This creates a combination of well controlled bass and those mids/highs that you're looking for with tubes.
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falconquest---been using solid state to drive the woofers for several yrs, everything from pro amps to integrateds and now a preamp & separate power amp. The issue is that the 45w I got out of my SET just wasn't quite enough some of the time. The SET broke down (again) so I sold it. I have a pretty good gainclone in the Audiozone Amp1 but it too is a bit lacking in power and just doesn't quite have the presence and inner detail of the SET so.... that's why I'm considering Class D finally. I hated the Wyred4Sound ST500 but I'm hearing that Class D has arrived. Hoping to either verify that or have the opposite confirmed. And I DO really like tubes but I've had enough issues with them and the replacement cost + it can be pretty difficult to source good tubes. Simplify! That's my goal in audio now as well as life. |
“Simplify! That’s my goal in audio now as well as life”.
If that’s indeed your goal then get high efficiency speakers > 96db and you don’t have to deal with this bi-amping crap (no offense) or high wattage amps. I went from 92dB to 96dB efficiency speakers and couldn’t be any happier. |
@icherekpal,
Okay I clearly understand your dilemma and why you’ve decided to move away from tube amplifiers. Less recurring cost and a gain in convenience and simplicity. I think you’ve spoiled your ears with the 805 SET😊.
If you find a class D amplifier that sonically comes close to the JAS Audio SET amplifier, please post and let us all know.of your successful acquisition. I wish you the best in your ongoing search.
Charles |
Replacing a good SET amp in the price range you specify isn't easy. Despite the inherent limitations of SET amps, they can indeed impart a certain magic to music, distortion and all.
I've moved on from SET. I found my destination amps with my Atma-Sphere M-60s. I had the M1 power supply and Vcap upgrades, and spent some effort in selecting driver tubes. It is fed by a 101D based tube preamp. That set up got me all the virtues of SET and none of the limitations. No looking back for me. But that option is outside your price range.
Ralph is not blowing smoke on his comments on what is really false dynamics in SET amps.
After my SET amps got bumped from my main rig, they went into my downstairs living room system. After spending a couple of years there, they got bumped again, this time by a Lyngdorf 2170 integrated. This is a class D amp that also contains a really good DSP feature. It is an amp that is hard to characterize. To my ears, it doesn't sound like SS, but it doesn't sound like an SET tube amp either. IF your source material is digital, and if you can benefit from digital room correction, this might be something to consider. You can get one used under 3K. It is not anything special in my estimation if you are an analog source guy.
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A used Lyngdorf 2170 is available for less than 3K USD? That could quite possibly be the way to go. Definitely worth serious consideration at the price point. Excellent recommendation from Bill (brownsfan).
Charles |
I tried the Legacy PowerBloc class D amp with my SE’s because I just had to know. I found it really did a great job controlling the bass but the mids and highs just lacked the nuance that my class A/B SS amp offers. That was the basis for my suggestion. I have been interested in moving to an integrated (hence my search for a tube integrated) and I’m not sure one exists either tube or SS that can match separates. I had a Plinius SA-103 which is 220w into 4 ohms class A and felt it lacked power. I moved up to the Plinius SB-301MKII which is 380w class A/B and the sound improvement was very noticeable. The SE’s seemingly love power. I’m not talking about overall volume but just the grip on the bass and the overall coherence of the sound. At least in my system. |
If a Pass Xa25 is in your realm you absolutely should audition one. Fantastic little amp. Not sure sure where it was ever called “colored”. Not. Pure class A awesome. |
purest sounding lowish power ss amps i have heard in my system are jun kimura san’s 47 labs gaincard and related peter daniel audiosector patek se (which i have still kept) ... not sure they will do their magic in your specific application
but you definitely trading something away when you leave SET amplification |
jjss49--The Audiozone Amp1 is (if I understand it correctly) also a Peter Daniel's creation and is pretty much the same amp with dual front mount volume pots and it is really quite nice. I keep the pots fully open and use the volume on my DAC. I run into volume limitations occasionally and that's mostly the reason I seek something else. It falls short of the JAS Array in some regards but I could live with it sonically.
lalitk--these DIY/Legacy Focus clones are quite sensitive. When going from the Von Schweikert VR 4 Gen II to these, I was shocked at how much louder these were than the VR 4's with the volume set at its customary setting. And I'm thinking replacing these would be a huge P.I.T.A . Getting something as good would be expensive and selling these....oh, easier to keep them!
geof3---i asked about the Pass xa25 vs the Gamut D100/200 recently as was told the Gamuts were quite a bit more transparent and the Pass were a warmer and smoother sounding amp. No criticism here, I would just prefer the greater transparency. I'm happy to use cables to adjust the sound as necessary
charles1dad---you're always a gentleman on these forums and offer good advice as well which probably puts you in the minority but I certainly appreciate that.
brownsfan----still spinning aluminum exclusively so digital it is! I'll look into the Lyngdorf. Love it when I get concrete options. Thanks |
@icherekpal,
Thank you for the kind comments.
Charles |
If your used to your SET tube sound, no class D will ever match the tone.
your better going more powerful tube amp, or a class A SS amp, or a nice class AB amp. |
It was just more detailed with subtleties that increased realism beyond
anything else. That's what I'm asking about in a possible Class D
replacement. Speaking from experience, the right class D amp can do that. Class D has as many variations as any other type of amp does, so just because one class D might not bring home the bacon says nothing about another. If your used to your SET tube sound, no class D will ever match the tone.
Again, speaking from experience, I've not found this to be the case. The main differences we hear in amplifiers are two-fold: what is the distortion signature, and how flat is the frequency response. SETs generate a lot of distortion. At full power its typically 10%. If you're really serious about using one, your loudspeakers should be efficient enough that the SET is never asked to make more than about 20-25% of full power (this will limit the higher ordered harmonic distortion that causes them to sound 'dynamic'). It should be noted that the dynamic nature of music should come from the recording, not the amplification! Now the advantage of SET is that as power is decreased to zero, the distortion drops to unmeasurable. This is the source of that 'magical inner detail' that so many talk about. Put simply, its that First Watt that is actually very good (unless you have a type 45-based amp, in which case it will be that first 100th of a watt). But SETs by no means rule the roost in this regard. Our amps have the same property of linearly decreasing distortion. Our amps are push-pull; that sort of quality in a push-pull amp is rare! But there isn't some sort of pixie dust that allows for it; you simply have to be aware of how amps make distortion, and what distortions are going to be heard by the ear. Any zero feedback tube amplifier that is fully differential from input to output will have this quality. Let's talk about the lower ordered harmonics for a moment. Its the 2nd order that makes SETs have that ever-lovin' tube sound- it give the amp a rich, warm quality and assists the ear/brain system in winnowing out detail and soundstage (that latter bit is IMO something that could do with more research as to why this is so). To this end, the 2nd harmonic is fairly innocuous. Other than making the amp a bit more euphonic, you don't hear it. The 3rd harmonic has this same quality- the ear treats it the same way. The presence of the 2nd and 3rd in sufficient quantity can mask the presence of higher ordered harmonics to a certain extent. This is part of why tube amps sound smoother than a lot of solid state. But that isn't the entire picture. The ear/brain system assigns a tonality to all forms of distortion. The lower orders mostly richness, the higher orders cause harshness and brightness even in tiny amounts. This is because the ear uses them to sense sound pressure and so has to be keenly sensitive to their presence. This is why many solid state amps have sounded bright- its entirely due to the higher ordered harmonics making themselves known. The problem has been feedback in amplifiers. If used in insufficient quantity, it will add distortion of its own while suppressing the innate distortion of the circuit in which its used. But- if you use **enough** feedback this will allow the amplifier to compensate for the distortion caused by feedback itself. Nelson Pass comments on this in an article he wrote about distortion. In it he speculates that you'll need more than 70dB of open loop gain (this is how much gain the amp has if there is no feedback). This is a very difficult number to achieve in traditional solid state amps since oscillation is a clear and present danger due to a phenomena known as phase shift. How that works is that at some frequency above the audio band, the phase shift of the amplifier starts to go up. When it passes about 90 degrees, the amp can use the feedback as positive rather than negative- and so oscillation can result. So many designers don't push their luck. But Luck has nothing to do with it. Sound engineering does, and some designers have succeeded in making amps of this type. The Benchmark is one example. There is another way to get around this problem. That way is to use a class D amplifier and use so much feedback that the amp goes into oscillation. But in this case, the oscillation is used as the switching frequency of the amplifier, so we're OK with that. Such an amp can have north of 40dB of feedback, allowing it to compensate not only for distortion caused by feedback but also phase shift caused by the output filter of the amp. Once either of these approaches are achieved, its then up to the designer to understand how the ear senses distortion and how the ear's masking principle works. If he does this right, then he will see to it that despite the resulting low distortion of the amp, the primary distortion components are still the lower orders. If he does this, the resulting amp will be smooth like tubes and will be extremely detailed at the same time. So you can get that 'magic'. The only downside is that any amplifier that does this will have a hard clipping character, so it will be important to have more than enough power to do the job- IOW you *never* clip the amp! The flip side of this is to avoid using any feedback at all, relying on other techniques to control distortion. Do there you have it. You can have an SET which has no feedback, or a class D which uses a ton of feedback, and the two can sound surprisingly similar (although IME you'll hear more detail from the class D, and of course it will have more power)! |
@icherekpal,
If you have an opportunity to hear amplifiers the subscribe to the high negative feedback (NFB) application as explained by Ralph, would you please share your listening impressions of them?
I’ve heard the Benchmark, Mola Mola and Soulution amplifiers (Examples of High NFB circuits) no SET sonic characteristics in my opinion. I don’t deny that many listeners loves these particular amplifiers and in fact I could be in the minority.
Given your very happy listening experience with the JAS Audio SET I wonder what your take would be. I in no manner dispute Ralph’s technical explanation, rather just relating my listening experiences. There's absolutely no doubt that we all hear things differently.
Charles |
Pretty much any good quality SS amp of any design and modest power capable of handling a varying load would be well suited to drive just a pair of satellites with bass crossed over elsewhere, Class D included.
SET or OTF would not be my first choice in that those typically require easy impedance loads to do their best which may or may not be the case here. Only measurements would tell for sure. Push/pull tube would be a safer bet if you must use tubes. Good SS or class D should have no problems whatsover.
With SET or OTF, it is always a good idea to seek speakers that are specifically designed to work with those well. IT's a different paradigm. Your choices will be more limited for best performance although subjectively any amp might still produce some good or pleasing results. Just not the best possible.
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Lots of quality recommendations and educational posts in here. Good luck with the search. I was going to tell you about my efforts in the same regard, but I went from 8W 300b SET monos to a 25W First Watt PP. Moving from 45W to 100W seems like a tall order. My journey was difficult and I think yours will be harder, especially with the budget limitations. Please do post back with updates regarding the journey...
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Just out of curiosity, I went over to usam and looked at the amps for sale between $2000 & $3000. Not that I think they’re going to sound like a SET, but three I’d be interested in trying if I were in your situation were the Ayre V-X5e (200W), Modwright Instruments KWA100 (100W), and the Carver Crimson 275 (75-90W). |
I’ve heard the Benchmark, Mola Mola and Soulution amplifiers (Examples
of High NFB circuits) no SET sonic characteristics in my opinion. I
don’t deny that many listeners loves these particular amplifiers and in
fact I could be in the minority. @charles1dad There is a reason that I mentioned the bit about the designer paying attention to human hearing rules (I didn't put it in quite those terms). If he's not careful, and does not permit the lower orders to mask the presence of the higher orders, the amp runs the risk of sounding dry. Now if you get the distortion low enough, this phenomena is reduced, but you have to get really low distortion numbers! 0.0001, that sort of thing. So if for whatever reason you can't get there, then you have to be sure that the lower orders mask the higher orders. To give you more insight on this, almost any solid state amp has less higher ordered harmonic distortion than almost any SET. But the SET has a huge 2nd order by comparison, which tends to mask those pesky higher orders. (Here's a fun bit: amps that make the 2nd ordered harmonic as their primary distortion component have what is known mathematically as a Quadratic Non-linearity. Amps that have a 3rd as the primary distortion have what is known as a cubic non-linearity. The difference is, if based on the 2nd the distortion harmonics do not fall off as quickly as they do if the 3rd predominates. Since the 3rd is treated the same by the ear as the 2nd (contributes to warmth and 'bloom') an amp that is based on the 3rd will still have a musical presentation, but otherwise will be perceived as being more neutral since there is less coloration overall (the 3rd will be slightly less than it is in an amp based on the 2nd harmonic) due to distortion. This is why I built entirely differential amplifier circuits, as the simple fact that they cancel even-ordered harmonics in each stage throughout the circuit caused it to have its major distortion component as the 3rd. Since distortion is not compounded from stage to stage, the higher orders fall off at a faster rate as the order is increased.) Obviously the brightness and harshness of traditional solid state that we've heard over the last 50 years (and why tubes are still around) is a coloration too. I don't agree that we hear all that differently: all humans use the higher ordered harmonics to sense sound pressure and all human's ear/brain systems assign the same values of brightness and harshness to these harmonics when they are distortion. IME people express these differences out of expectations of what a stereo should be, if not sounding real. When you ask for the music to sound real, then (again IME) these differences tend to go away and people start hearing the same things. |
I have a Sciit Ragnarok which I like a lot. It is probably class AB and I have not compared it to many others. Around $1.7k. |
Ralph,
I understand that we humans hear the same in regard to neuro-acoustical physiology pathway or msechanism (Using higher order harmonics to gauge sound pressure and detecting harshness and brightness). I should have been more clear as I’m referring to individual taste/preferences IOW the subjective aspect.
You used the term "dry" and that describes how the 3 amplifiers I cited sound to me (Definitely a subjective judgement). Someone else may describe them as accurate and very neutral. This is the hearing/perceptive differences I was referring to.
Charles |
@atmasphere I appreciate your explaination and the educational post Ralph, but I will note that some listeners do find substantial differences between 2nd vs 3rd harmonic dominant designs (e.g., see the "Harmonic Distortion and Sound" section of this article: https://www.passdiy.com/project/articles/audio-distortion-and-feedback). This even holds when the amplifier typology is otherwise held constant, e.g., when adjusting the front control on the First Watt SIT-1. |
Charles---I probably won't (ever) be able to swing the Mola Mola or Soulution amps but am interested in the Benchmark. I'd be much more likely to seek them out if the used price were lower though. How did you feel about the Benchmark's sound? I read a few comments about some incompatibility issues with some speakers?
Mapman---these Focus clones are a fairly good match with 805 based SETs. The 45w is ample power for the most part. I just get the itch sometimes to play lounge or dubstep or some brutal bass heavy ambient at un-neighborly levels. With almost everything else, I never felt I was pushing the JAS hard. My main listening was jazz and some blues so the volume was usually kept at reasonable levels. With most other SET amps using other tubes, I would agree with finding the right speakers but I think it less of an issue with 805's.
articdeth---my appreciation of the SET I had was more based on it's pristine sound than tone. With the right recordings, I was hearing the musicians in the room with me rather than a widow on to the recording. There was just so much inner detail and (almost) nothing between me and the sound. Almost every other amp I've used is veiled in comparison. I'm looking for the transparency and detail I hear about in the best Class D amps without the common shortcomings. The reviews of some of the First Watt amps sound like what I want, just much more power.
atmasphere---you mention that there are Class D amps you've heard that are very close to the SET sound. Would you please offer a recommendation or two?
Many thanks to all. If I find what I'm looking for, I'll certainly share my experience(s). |
@lcherepkai
1. I've also heard that about the Benchmarks. My impression is that they are not capable of handling low impedance loads, and (perhaps surprisingly) it seems this becomes more of an issue if you're running them as monoblocks. If you're thinking about them, I'd just reach out to Benchmark with your speaker specifications and ask about compatibility. From all reports they're great amplifiers. As Charles mentions, the comparison of this high- feedback amplifier typology to your SET experience will be very interesting. There are some used units around and I think you can get some new ones with free home trials, so it might be easy to find out.
2. Hopefully Ralph will weigh in but unfortunately I suspect @atmasphere is referencing his own Class D amplifier that is currently under development. I'm sure it'll be wonderful, but not yet available and perhaps outside your budget. |
@icherepkal,
I will 2nd your request of Ralph to identify these special SET sounding high NFB class D amplifiers . I’m "genuinely" interested in who are the manufacturers capable of what I’d consider a very admirable feat. They deserve exposure and recognition. I can’t deny some may exist but I’ve yet to come across any thus far. Obviously I haven't heard every class D amplifier in existence.
Charles |
The Benchmark AHB2 doesn’t have a "sound" it’s one of the best measuring amps around. If your speakers and ears can take it you can push 120dbspl and the noise floor will still be -10dBSPL below. If there was ever an amp considered neutral it’s the AHB2. |
Depends how low the impedance of the speaker is. The Benchmark can do 500 watts bridged into 4 Ohms at .00026% distortion. If the speaker hangs around 2 Ohms they don't reccomend you use them bridged. |
I wouldn’t deny for a nanosecond that there are listeners who would love the Benchmark sonic presentation. Every audio component has a "sound" or individual signature. In the past I recall similar declarations about the defunct Halcro amplifiers. Dead on accuracy and sonic neutrality with breathtaking bench measurements.
Charles |
As the late (And great) Al use to point out , when you bridge an amplifier the speaker impedance load (As seen by the amplifier) is halved. So a 4 ohm load becomes 2 ohms and so on.
Charles |
I thought Halcro Audio is no longer an active manufacturer and I may be wrong in that regard.
Charles |
@charles1dad As @twoleftears suggests, my bet is on the AGD amplifiers as the most SET sounding class D design (GAN-based). I'd love to hear them. They certainly want to convince us that they care about SET musical characteristics with the design, and one dealer advertisement states that SET people do like them ( https://www.youtube.com/watch?v=2PKSlTODkJ0). Unfortunately more than double the OP's budget. |
And thanks for channeling @almarg for the technical reminder about why the Benchmarks would struggle when in bridged mono mode. It makes total technical sense, but is ironic that when configured to deliver the most power, they also lose the ability to deliver the needed current into low Ohm loads. Unfortunately this is likely the exact kind of case in which one would actually need the additional power. Watts are cheap... until they aren't. |
Hi cal,
Yes, as we all recall Al was excellent with his (Always) clearly written, detailed yet easy to comprehend technical explanations. Bridging amplifiers is but one of many examples where Al offered clarification and when necessarily caution. I learned much from him.
Charles |
2. Hopefully Ralph will weigh in but unfortunately I suspect @atmasphere is
referencing his own Class D amplifier that is currently under
development. I'm sure it'll be wonderful, but not yet available and
perhaps outside your budget. We are working on a class D amplifier which has reached beta production. Its intended pricepoint is about 5000.00/pair. Although I think our amp is doing quite well as far as being musical is concerned, I was not talking about it specifically. I was more talking about how feedback is troublesome if improperly used (which is about 99% of the time). The Benchmark is an example of an amp that does feedback properly. Self oscillating class D amps are another example. Feedback has gotten a bad rap and deservedly so because if you don't run enough of it (and that's been the case in the last 60 years), it will generate higher ordered harmonics and IMD at the feedback node (unless you are very careful about the latter). This causes harshness and brightness, and this is the main reason transistors are harsh and bright. If you run feedback in tube amps, they get harsher and brighter too (and this will be in spite of the fact that the frequency response is actually **flatter**, because the brightness is caused by distortion, not a frequency response error). So we've seen designers, including myself, building zero feedback amplifiers to prevent this brightness and harshness. You can think of the use of feedback as being on a bell curve, use a tiny bit and its not bad but doesn't do a lot, use more and the distortion issues increase (all the while suppressing the innate distortion of the circuit, so it will measure well but not sound as good as the specs suggest). But finally you get to the other side of the curve, which is at about 35-40dB (meaning that if the amp had no feedback, it would have to have at least 65-70dB of gain!). At this point there is so much feedback that it allows the amp to compensate for the distortion generated by the feedback, and corrects phase shift too. One thing I forgot to mention is how distortion can increase at higher frequencies if feedback is insufficient. You really want the distortion to be the same regardless of frequency. Our OTLs can do this, which is part of why they are musical, and the smaller the SET, the more they can do that as well (this is part of why the lower powered SETs are held in such high esteem). To cover up this problem, the distortion specs you see are usually done at 100Hz! If you measure the distortion spectra at 1KHz you get far more meaningful information- look at what the amp is then doing at 7KHz, which is in the area where the ear is most sensitive (birdsong frequencies). The 7th harmonic is unpleasant! If you measure at 100Hz, the 7th harmonic can often appear benign. This is why many solid state amps seem to do bass just fine, because at bass frequencies, they really **are** doing just fine because there's enough feedback. But as frequency is increased, the amp can run out of Gain Bandwidth Product, which is a way of saying that the feedback is being reduced. This is a very common problem! My experience with monostrapping and bridging amplifiers isn't good. The amps almost always get less musical (higher distortion). Lower impedance loads can be an issue as well because the current expected of the output devices might be exceeded, such as into 2 ohms- that leads to failure and shipping costs... I miss Al as well. He was a friend, a good egg and always steady on. |
I have heard class d and am not impressed at all i would look for a great vintage amplifier with a solid state ab output stage from a good company in that 2 to 3 k range you will get much better sound than a class d amplifier I have 18 amplifiers of that type and they all sound better than a class d amplifier.
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Hello lcherepkai! I recently replaced my 300B, 8 wpc, Elekit 8600-RS with a Starke Sound A4-320. Four channels (can be bridged), Class D, absolutely glorious sound - a rival of the Purifi Audio module in the NAD M33 and the LKV power amp. It beats the 300B amp and has extremely tight control of the speakers it feeds. I have two A4-320s and two of the Purifi Audio EVAL1 kits (also Class D) they are simply unbeatable. Read the reviews. The Starke gives you four channels (for bi-amping maybe?) for under $2000 while LKV wants $10k for two. Same super quality sound, no kidding. The secret is very high frequency "swtching" in the class D amp - 600khz. Try it, you will love it
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