It would be interesting to know the findings of those who have used a ( stand alone ) tube input stage for a ss power amp.
Of particular interest would be plain cathode follower and plate follower stages using triodes. These can be configured several ways .
I found some conflicting differences in some implementations. In one power amp the cathode follower appeared to sound more 'powerful' than a plate follower ( regular stage with some gain and with plate and cathode resistor load and no cathode bypass cap ). In another power amp it was the reverse. I did ensure that there was no difference in the caps in series with the signal.
It might be interesting to know if anyone found any SQ advantage using a tube input.
In my case I felt that the sound improved marginally particularly at the lower end. Could be because of the high Zin of the tube stage and no input cap. However a plate follower with a little gain didn't seem to make much of a difference. This also had a high Zin and no input cap.
Zout would have been much higher ! So the combination of capacitorless high Zin and low Zout as seen by the power amp might might sometimes become quite audible.
This could be replicated with a FET input opamp , but would it sound the same as a tube ? I didn't find the tube's increased H2 distortion made any audible difference . Like the mid range didn't sound any 'warmer' or 'tubey!'!
It did degrade the SN ratio , though it was still quite low. However hum from the heater was audible right next to the speaker ( ac heater ) though not audible at the listening position. No doubt the amp would measure much worse for distortion or SN ratio than the plain ss amp if a ( stand alone) tube input stage is used.
Of particular interest would be plain cathode follower and plate follower stages using triodes. These can be configured several ways .
I found some conflicting differences in some implementations. In one power amp the cathode follower appeared to sound more 'powerful' than a plate follower ( regular stage with some gain and with plate and cathode resistor load and no cathode bypass cap ). In another power amp it was the reverse. I did ensure that there was no difference in the caps in series with the signal.
It might be interesting to know if anyone found any SQ advantage using a tube input.
In my case I felt that the sound improved marginally particularly at the lower end. Could be because of the high Zin of the tube stage and no input cap. However a plate follower with a little gain didn't seem to make much of a difference. This also had a high Zin and no input cap.
Zout would have been much higher ! So the combination of capacitorless high Zin and low Zout as seen by the power amp might might sometimes become quite audible.
This could be replicated with a FET input opamp , but would it sound the same as a tube ? I didn't find the tube's increased H2 distortion made any audible difference . Like the mid range didn't sound any 'warmer' or 'tubey!'!
It did degrade the SN ratio , though it was still quite low. However hum from the heater was audible right next to the speaker ( ac heater ) though not audible at the listening position. No doubt the amp would measure much worse for distortion or SN ratio than the plain ss amp if a ( stand alone) tube input stage is used.
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There's not just 'one answer' to your question. It's entirely dependent on what you're trying to achieve. Does sound quality mean minimum distortion or some subjective musical impression? What tubes will be used in what configuration, topology, build quality, next stage's input impedance etc. etc. There's a lot to it.
A tube circuit can be very linear and very transparent. If 'tube sound' is what you're after, you can build an effects box.
A tube circuit can be very linear and very transparent. If 'tube sound' is what you're after, you can build an effects box.
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my personal experience
I did use a tube preamp to drive a solid state amp before I bought a tube power amp. I wanted to see if tubes really did sound better. Now, for whatever reason, I thought it did sound better. I used it to drive one of the best SAE amps. I had two very good-sounding solid state amps, the SAE and an Adcom. It was hard to say which sounded better. So, that gives you an idea of the quality of the solid state amp in question.
I did notice that the tube preamp added a LOT of compression. That may have been why I thought it sounded better. Compressors make the music SEEM louder. That experiment was from several years ago. I have learned a lot since then, and my opinion is that it was probably because of the high input impedance and the compression. The best results I have obtained in my many experiments have been with JFET input stages in tube amps. Back in the 90s, a friend of mine replaced the input stage transistors on a transistor amp of mine with JFETs and I was pleasantly surprised by how much they improved the sound quality. Very tube-like if you use good JFETs.
I suspect there is a lot of "it depends" involved in answering your question. If you want to experiment, I'd suggest just whip up a simple tube preamp with some of the better quality dual-triode tubes like the 6SN7, or 6CG7 or the Russian 6N6P. or the Russky version of the 6SN7. The 12au7 is okay, but doesn't sound as good (IMO).
I did use a tube preamp to drive a solid state amp before I bought a tube power amp. I wanted to see if tubes really did sound better. Now, for whatever reason, I thought it did sound better. I used it to drive one of the best SAE amps. I had two very good-sounding solid state amps, the SAE and an Adcom. It was hard to say which sounded better. So, that gives you an idea of the quality of the solid state amp in question.
I did notice that the tube preamp added a LOT of compression. That may have been why I thought it sounded better. Compressors make the music SEEM louder. That experiment was from several years ago. I have learned a lot since then, and my opinion is that it was probably because of the high input impedance and the compression. The best results I have obtained in my many experiments have been with JFET input stages in tube amps. Back in the 90s, a friend of mine replaced the input stage transistors on a transistor amp of mine with JFETs and I was pleasantly surprised by how much they improved the sound quality. Very tube-like if you use good JFETs.
I suspect there is a lot of "it depends" involved in answering your question. If you want to experiment, I'd suggest just whip up a simple tube preamp with some of the better quality dual-triode tubes like the 6SN7, or 6CG7 or the Russian 6N6P. or the Russky version of the 6SN7. The 12au7 is okay, but doesn't sound as good (IMO).
I was asking for the opinion of others on what they think of the sound when ( if !) they added a tube input stage to a solid state power amp. From what you wrote, looks like you didn't try it out.
Thanks for your post anyway.
This is interesting. I actually found that in one implementation it sounded very dynamic. Bass also appeared more extended ( NOT bass boost !). Transients had more impact and weight. Very satisfying sound. However I can't say if that's what the original was supposed to sound like !
I'm sure this is also tube dependent. I've been trying various things over the years and some schemes are very 'interesting' ! I have all those tubes you mentioned though right now I'm currently using a Sovtek 6922. I also find that one has to be really careful with ac heaters if we have to avoid heater supply hum from coming through. Never tried comparing between ac/dc heater supplies. They say ac heater supplies are good for heater filament life.
Yes I have tried it out, in several ways, with several amps. And my conclusion is exactly what I'm trying to tell you. A tube pre, in the broad sense you're question's about, will neither have a definitive positive or negative effect on sound quality.
A crappy tube pre will sound worse than a proper SS pre and vice versa. Possible there's no audible difference at all (most buffers). Just like an awesome tube pre in the wrong place will never shine.
It's always dependent on the chain it's a part of. Signal levels, in- and output impedance etc. And again, there are both awesome and horrible tube pre's. Just as there are awesome and horrible SS preamps.
Then there's the issue that 'sound quality' is VERY subjective to say the least. You'll likely get many biased opinions and impression. They're subjective and really only applicable to the situation and listener in question. IOW useless.
So, the application and personal preference determines if there's any benefit to be gained from a tube pre, NOT the fact the pre happens to have some glass in it.
Edit: A tube stage is nothing by itself. It can be used to described many many different topologies. CC, CF, WCF, SRPP, SRPP+, Futterman, Mu-follower, etc. Or PP, SE, Xformer or OTL.
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You are right , like in all of audio, there are many ways of doing things and getting varied results. No single best way !
Is there any simple configuration you tried that sounds really good...according to you ?
I had mentioned that the stage should be a triode in cathode follower or plate follower mode.
I am guessing that more complex schemes will potentially fare better. Like for example the Aikido which many builders claimed did work very well for them.
Cheers.
Is there any simple configuration you tried that sounds really good...according to you ?
I had mentioned that the stage should be a triode in cathode follower or plate follower mode.
I am guessing that more complex schemes will potentially fare better. Like for example the Aikido which many builders claimed did work very well for them.
Cheers.
Just found an interesting thread on heater supplies at http://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-good-bad-ugly.html
The very faint hum I hear at the speakers is not 50 Hz but 100Hz . I do have a virtual center point for the ac heater connected to an elevated point ( 30 V I think !).
The very faint hum I hear at the speakers is not 50 Hz but 100Hz . I do have a virtual center point for the ac heater connected to an elevated point ( 30 V I think !).
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Probably a nice addition if you are into "euphonic tube distortion" - or something. Otherwise it's probably an entirely useless addition. Yes, a tube can be configured as a practically transparent element as well. But what's the point of that if sans tube provides exactly the same outcome?
If I understood correctly, we are talking about amps where a tube stage isn't exactly a mandatory addition.
And it's important to acknowlege that when we discuss about vague concepts such as "tube like", "tubey", etc. a single tube gain stage isn't the same thing as an entire tube amplifier.
If I understood correctly, we are talking about amps where a tube stage isn't exactly a mandatory addition.
And it's important to acknowlege that when we discuss about vague concepts such as "tube like", "tubey", etc. a single tube gain stage isn't the same thing as an entire tube amplifier.
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You are right , like in all of audio, there are many ways of doing things and getting varied results. No single best way !
Is there any simple configuration you tried that sounds really good...according to you ?
I had mentioned that the stage should be a triode in cathode follower or plate follower mode.
I am guessing that more complex schemes will potentially fare better. Like for example the Aikido which many builders claimed did work very well for them.
Cheers.
To be honest, I've yet to hear a tube pre that sounds significantly better than a SS pre of similar quality. Same goes the other way round (for the record, guitar/bass amplification is an entirely different story).
BUT I just love the glass envelops, glowing heaters, high voltages and the notion the 'audio signal' is actually traveling through the vacuum! The reason I use a tube pre is mainly psycho acoustical (not to be underestimated) and my experience is tube pre amps tend to be constructed with more care.
Might be ripple from the power supply. Do you own an oscilloscope?
Very true
, Yes a glowing tube does 'look' more exciting !You are quite right about 'psycho acoustical' factors. Tube pre amp construction does need more care . Actually it could be far more expensive than a decent ss preamp depending on what tube and supplies we use.
Yes,I have a scope and other test equipment.Haven't had time to check out the design ( which is operational right now). Probably will try to do it over the weekend if I don't get stuck with other issues.
Cheers.
ac versus dc
I have found that rectifying the heater current often solves the power supply hum problem when nothing else will.
There is no reason I can fathom that would make ac the better choice in terms of heater longevity. I CAN see how DC would be better. The peak voltage exposed to the heater would be lost, and thermal stresses could only be less, not more.
When you rectify ac, the resultant "ripple" is twice the mains frequency. So, you should expect to hear 100 Hz in your country and 120 Hz in America.
I have found that rectifying the heater current often solves the power supply hum problem when nothing else will.
There is no reason I can fathom that would make ac the better choice in terms of heater longevity. I CAN see how DC would be better. The peak voltage exposed to the heater would be lost, and thermal stresses could only be less, not more.
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I'm using ac for the heater. So there is no rectified signal there.
I don't remember the details but I think I read the explanation somewhere on this forum , along time ago. It's the fact that the ac heater voltage goes through a zero every cycle that's supposed to be good . For what I can't remember.
Maybe it's related to what Bigun just said !
My very faint 100Hz hum could be leaking in from the plate suppy though it is filtered quite well. Maybe just some grounding error ! I'll have to study this well. I will use an external dc supply eventually to see if that really does eliminate the hum. If not, then I need to look elsewhere.
However I'm not too concerned because the 'hum' or 'buzz' is so low I can only hear it right next to the drivers cone. But it does drive me batty that it's there !
I don't remember the details but I think I read the explanation somewhere on this forum , along time ago. It's the fact that the ac heater voltage goes through a zero every cycle that's supposed to be good . For what I can't remember.
Maybe it's related to what Bigun just said !
My very faint 100Hz hum could be leaking in from the plate suppy though it is filtered quite well. Maybe just some grounding error ! I'll have to study this well. I will use an external dc supply eventually to see if that really does eliminate the hum. If not, then I need to look elsewhere.
However I'm not too concerned because the 'hum' or 'buzz' is so low I can only hear it right next to the drivers cone. But it does drive me batty that it's there !
As was mentioned previously, your question as it stands is wide open. But I would venture to say that if any definite improvement would be noticed, that indicates a poor 'match' between power and pre-amp - which will reflect on either an improper pre-amp output stage design or power amp input impedance. There is no excuse for either.
Well, certainly a plate follower with an unbypassed cathode will have a high output impedance not capable of driving many power amplifiers. (I frown on power amplifiers with input impedances of as low as 20K, unless made to suit a same make pre-amp. It is poor and unnecessary design.)
Thus in general, should you detect a definite difference, either amplifier or both have questionable designs.
(And you should not worry about an input capacitor - it is a short at audio frequencies. But that is a different subject, frought with snake oil dressing of all kinds of pseudo-science.)
Well, certainly a plate follower with an unbypassed cathode will have a high output impedance not capable of driving many power amplifiers. (I frown on power amplifiers with input impedances of as low as 20K, unless made to suit a same make pre-amp. It is poor and unnecessary design.)
Thus in general, should you detect a definite difference, either amplifier or both have questionable designs.
(And you should not worry about an input capacitor - it is a short at audio frequencies. But that is a different subject, frought with snake oil dressing of all kinds of pseudo-science.)
and i would disagree vehemently
I noticed early on that an amp could be broken down into constituent components. At it's most elemental, a power section and a preamp section. I also noticed that it was quite possible to "mix-and-match" preamp sections with the power sections (within certain limitations). My own personal experimentation proved to me beyond any shadow of any doubt that preamp design affects the overall sound quality of the amp dramatically and impedance matching has/had nothing to do with it.
I eventually went on to create my own design which has, to date, stood head and shoulders above any of the "classic" preamp designs, at least among those I have tried, and I tried many. Again, having nothing to do with impedance matching.
I noticed early on that an amp could be broken down into constituent components. At it's most elemental, a power section and a preamp section. I also noticed that it was quite possible to "mix-and-match" preamp sections with the power sections (within certain limitations). My own personal experimentation proved to me beyond any shadow of any doubt that preamp design affects the overall sound quality of the amp dramatically and impedance matching has/had nothing to do with it.
I eventually went on to create my own design which has, to date, stood head and shoulders above any of the "classic" preamp designs, at least among those I have tried, and I tried many. Again, having nothing to do with impedance matching.
Apology Jerrys - I think there is a misunderstanding in terms here.
I meant that in general hi-fi practice, a pre-amp is supposed to have an output impedance well below the power amp input impedance. In that way one can generally combine commercial units of one's choice. In other words, the output impedance of a pre-amp should not be loaded with a power amp's input impedance; that could/would change the pre-amp characteristics. Such impedances are usually mentioned in the specs for clarity. I was not talking about the rest of the design - certainly that will have an influence on sound quality. I certainly also did not mean to criticise your design; do realise that it was not mentioned or I did not see it; I presumed commercial units and general practice. Again, apology for unintentional offense.
But respectfully one cannot say that the mentioned impedances have 'nothing do with it', as explained in the previous paragraph - if I understand you correctly. (In this respect I should not use the term "match". Matching in audio and r.f. lore means an output impedance feeding an equal input impedance; that is not the general procedure in hi-fi amplifiers. Again, as explained above.)
I meant that in general hi-fi practice, a pre-amp is supposed to have an output impedance well below the power amp input impedance. In that way one can generally combine commercial units of one's choice. In other words, the output impedance of a pre-amp should not be loaded with a power amp's input impedance; that could/would change the pre-amp characteristics. Such impedances are usually mentioned in the specs for clarity. I was not talking about the rest of the design - certainly that will have an influence on sound quality. I certainly also did not mean to criticise your design; do realise that it was not mentioned or I did not see it; I presumed commercial units and general practice. Again, apology for unintentional offense.
But respectfully one cannot say that the mentioned impedances have 'nothing do with it', as explained in the previous paragraph - if I understand you correctly. (In this respect I should not use the term "match". Matching in audio and r.f. lore means an output impedance feeding an equal input impedance; that is not the general procedure in hi-fi amplifiers. Again, as explained above.)
sorry, somewhat misunderstood
I thought you were echoing a statement I have heard others make, even electrical engineers, which is that the preamp doesn't matter. To that notion, I would vehemently disagree. I didn't post my design. It confuses people , so I don't "push" it on anyone. Most of the folks who contact me want something simple that sounds good, so they want a circuit they can understand, and I accommodate them. Priority #1 for me is sound quality, then simplicity. Some who contact me are tube purists and won't allow solid state in, period.
I'm just interested in what works, so I experiment a lot. And before I go way off topic here, I'll sign off.
I thought you were echoing a statement I have heard others make, even electrical engineers, which is that the preamp doesn't matter. To that notion, I would vehemently disagree. I didn't post my design. It confuses people , so I don't "push" it on anyone. Most of the folks who contact me want something simple that sounds good, so they want a circuit they can understand, and I accommodate them. Priority #1 for me is sound quality, then simplicity. Some who contact me are tube purists and won't allow solid state in, period.
I'm just interested in what works, so I experiment a lot. And before I go way off topic here, I'll sign off.
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I remember reading this little dissertation by a guy who knows his stuff and he was saying there's two ways of approaching it, one is the idea of sufficient voltage (from the driving circuit) to drive the driven circuit, and the other school of thought is the impedance matching for maximum power transfer. I took electronics. My brother did a full-on 2-year course (Avionics). He talked about impedance matching for max power transfer quite a bit, but it was generally in the context of radio circuits. I experienced first-hand what you are talking about with impedance, especially in the context of tone control circuits and electronic crossovers. Sometimes you gotta use buffers. I ended up making my own electronic crossover 'cause the cheap chinee crap doesn't last and the rest is overpriced. The circuit was just dirt simple and worked BETTER (as in sounded better) than a Rane brand crossover (600 bucks new). I also try to keep the cable runs short, shielded because of the roll-off, unshielded because it's unshielded. I try not to use a lot of stages 'cause the more stages, the more the sound loses it's pretty. So, I tend to be minimalistic and won't add a stage, even a buffer, unless it's necessary for sound quality. I have had EE's tell me that I should use op amps and I'm imaging it when I say I don't like the sound. They point at the numbers (specs) for the op-amps. Logically, if the numbers are all there is to it, then we should be using op amps, solid state. To my ears, there has to be more to it 'cause I seem to get much better results by excluding op amps, outstanding specs notwithstanding, and I believe that is because of all those stages in an op amp. Apparently I'm not the only person "imagining it."
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