IF you read carefully, you will find that one requirement for his test is to modify one of the amps to make it like the other amp by adding passive components to his discretion.
I find his requirements to be invalid for a proper test to determine if the amps can be differentiated "as they are normally used".
Under his conditions, he is modifying one or more amps and it is no longer a valid comparison.
Never tried, and the plane ticket would be a bit out of my budget. 😀 He was smart enough to limit things to commercially available amps so that I can't build something deliberately noisy (for example) to get around the test conditions.
It would not be a "valid comparison" if the claim had been that any two amps sound the same. But that never was the claim, and this is quite explicitly stated in the challenge rules.
One of the most significant things that emerges from the DB tests, it seems to me, is that by means of simple (and cheap) equalisation applied to an SS amp, it can be made to sound like a tube amp. That seems to indicate that there is no mystique to the notion of "tube sound"; it is simply the easily-reproducible consequence of certain frequency-response and output impedance characteristics.
Chris
Makes you wonder about the subjective posters that have been going on and on after 3rd page of this thread, if they actually read the sources linked and understand the content.
I didn't read far enough.
Interesting results, particularly if one presumes that tests have been performed with SE tube amps which are supposed to be distinguishable due to the higher harmonic distortion levels.
If his assertion is correct, then what if anything does it say in relation to claims of one tube over another sounding different / better ?
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By this time I must keep it short or the "helmet'" will appear to lambast me for repetition ......
Evenharmonics,
Quite. But when Chris says that tube sound "is simply the easily-reproducable consequence of certain frequency-response and output impedance characteristics" ... I thought that by now it has been established that those are not the necessary/inherent characteristics of tube amplifiers.
Thus [also to SY who says that there is a difference between tube-sound and ss-sound (if I am correct?!)], yet again: Are we talking about the general (define!) sound of many tube amplifier designs, or are we saying that tube sound is inherent as in unavoidable in the topology?
I would respectfully repeat that that is a fallacy, as many decent tube designs can prove. Yet there seems to be this stubborn notion that tube amplifiers will have limited bandwidth and cause an intrinsic effect by relatively high output impedance (all of which of course affecting audible results).
So are we using existing (and respectfully, often inadequate) designs as a standard, or proper correct designs with none of the above limitations, of which many exist as said?
I expected objection to some of my statements in my post #387; I regard the fact that none came as agreement. Then my above question is even more relevant.....
Evenharmonics,
Quite. But when Chris says that tube sound "is simply the easily-reproducable consequence of certain frequency-response and output impedance characteristics" ... I thought that by now it has been established that those are not the necessary/inherent characteristics of tube amplifiers.
Thus [also to SY who says that there is a difference between tube-sound and ss-sound (if I am correct?!)], yet again: Are we talking about the general (define!) sound of many tube amplifier designs, or are we saying that tube sound is inherent as in unavoidable in the topology?
I would respectfully repeat that that is a fallacy, as many decent tube designs can prove. Yet there seems to be this stubborn notion that tube amplifiers will have limited bandwidth and cause an intrinsic effect by relatively high output impedance (all of which of course affecting audible results).
So are we using existing (and respectfully, often inadequate) designs as a standard, or proper correct designs with none of the above limitations, of which many exist as said?
I expected objection to some of my statements in my post #387; I regard the fact that none came as agreement. Then my above question is even more relevant.....
John, (not meaning to answer for Sy) are you asserting that properly designed tube amps (low output impedance, broad frequency response and good phase margin) are thus not distinguishable from SS amps.
If so, then why build tube amps?
If so, then why build tube amps?
Why build SS amps? They tend to be more sensitive to RF interference. They are more complicated, for a given performance level. More likely to fail if the output is shorted. 😎TheGimp said:
Just because I can !
. . . while tubes amps are more likely to fail if output is open 😀
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Perfect answer. The one I gave in a different thread was, "Why drive an immaculate '57 T-Bird?"
If you meant that they have read the sources linked and understood the contents quite (well), then the poster just before you debunked you by saying that,
In Clark's amp comparison, tube p-p amp when compared to transistor p-p amp, the reason that made audible difference turned out to be tube amp's frequency roll off, enough to the point of audibility. When eq is applied to transistor p-p amp (which had more linear frequency response than that particular tube p-p amp) to mimic that tube amp, the listeners could not distinguish the two by their ears only. In that particular case, the tube amp's difference was the frequency response and not some mystical property of tube amp.
I've measured FR of Dynaco ST-70 and Mark IV with original circuit design and they showed high frequency roll off, more than typical transistor p-p amp. I'm not saying all tube p-p amps do that in FR but it's more common than transistor p-p amps.
When I chose to mess with tubes (after much nagging from an old Tektronix friend who's now arguably a "Tube Guru), I wasn't sure if all the hassle of tubes would make a significant difference in a Hi-Fi system that's never overdriven, but I knew it would make a big difference in guitar amps where I would want to generate distortion for effect. So being a guitarist as well as an Audio Engineer, I went down that path initially.
My theoretical approach to distortion generation was OK, but not the best. I eventually realized that the best sounding distortion is the result of a variety of distortion mechanisms working together, sometimes independantly and sometimes sensitive to what the other distortion mechanisms are doing. A certain amount of randomness seemed like a good thing. There's also the changing in real time loading, of the output tube and output transformer, by the speaker load, the impedance of which varies both instantaneously and over frequency. Bob Carver talks about how the speaker acting simultaneously as a microphone brings a listening room echo signature into the mix through the negative feedback input port. How complicated would you like for this to get?
Sure there's the soft clipping and 2nd harmonic generation, and limited higher order harmonic generation, and the limited I.M. generation due to the low or no negative feedback.
Now I've got a pentode front end with an RC on the screen grid that messes with dynamics (apparently in a good way), I've then got the "fullwave saturator" 12AX7 topology that Fender (and others) used often in the early years (probably still - haven't looked lately at newer designs), then the tone stack, master vol. and single ended output stage (EL34) driving a P10R Jensen reissue driver in a solid pine cabinet. The sound is actually addictive. I can't stop playing sometimes. My bandmates put up with me having these occasional spurts of obnoxiousness, spewing some lead guitar riff.
When I enter a bar where a band is playing and it sounds like fingernails on a blackboard, I often find that it's that the guitar amp is transistor or that there are many solid state foot pedals in the signal path. So it's easy for me to suspect that tubes could sound better than transistors in a Hi-Fi system.
The higher output Z of a tube amp would allow the woofers to resonate and ring a little bit more, creating "warmth". The generation of 2nd harmonic distortion, and limited higher order harmonics could make the midrange sound more pure and musical. I'm not sure which one wins above 7kHZ. Probably depends more on how the circuit is designed (phase margin, recovery from clipping, crossover distortion, ringing, regeneration of I.M. products due to recirculation around the negative feedback loop.
Now I have a half circle of surround sound setup, mostly transistor/chips and tubes on just the tweeters of my main open baffle triamp'd speakers. There isn't the physical space to do everything in tubes.
Having said all of this, I believe that the weakest link in any Hi-Fi system is how the speakers interact acoustically with the room. A close second would be the speakers themselves in any other ways. Third would be how the recording was mic'd/mixed/processed. Past a certain point, I just don't care. It sounds great, now let's go fishing, if ya dig.
My theoretical approach to distortion generation was OK, but not the best. I eventually realized that the best sounding distortion is the result of a variety of distortion mechanisms working together, sometimes independantly and sometimes sensitive to what the other distortion mechanisms are doing. A certain amount of randomness seemed like a good thing. There's also the changing in real time loading, of the output tube and output transformer, by the speaker load, the impedance of which varies both instantaneously and over frequency. Bob Carver talks about how the speaker acting simultaneously as a microphone brings a listening room echo signature into the mix through the negative feedback input port. How complicated would you like for this to get?
Sure there's the soft clipping and 2nd harmonic generation, and limited higher order harmonic generation, and the limited I.M. generation due to the low or no negative feedback.
Now I've got a pentode front end with an RC on the screen grid that messes with dynamics (apparently in a good way), I've then got the "fullwave saturator" 12AX7 topology that Fender (and others) used often in the early years (probably still - haven't looked lately at newer designs), then the tone stack, master vol. and single ended output stage (EL34) driving a P10R Jensen reissue driver in a solid pine cabinet. The sound is actually addictive. I can't stop playing sometimes. My bandmates put up with me having these occasional spurts of obnoxiousness, spewing some lead guitar riff.
When I enter a bar where a band is playing and it sounds like fingernails on a blackboard, I often find that it's that the guitar amp is transistor or that there are many solid state foot pedals in the signal path. So it's easy for me to suspect that tubes could sound better than transistors in a Hi-Fi system.
The higher output Z of a tube amp would allow the woofers to resonate and ring a little bit more, creating "warmth". The generation of 2nd harmonic distortion, and limited higher order harmonics could make the midrange sound more pure and musical. I'm not sure which one wins above 7kHZ. Probably depends more on how the circuit is designed (phase margin, recovery from clipping, crossover distortion, ringing, regeneration of I.M. products due to recirculation around the negative feedback loop.
Now I have a half circle of surround sound setup, mostly transistor/chips and tubes on just the tweeters of my main open baffle triamp'd speakers. There isn't the physical space to do everything in tubes.
Having said all of this, I believe that the weakest link in any Hi-Fi system is how the speakers interact acoustically with the room. A close second would be the speakers themselves in any other ways. Third would be how the recording was mic'd/mixed/processed. Past a certain point, I just don't care. It sounds great, now let's go fishing, if ya dig.
Thanks Sire; I dig. Not being a guitarist myself, very informative post, thanks.
For that to happen the nfb-design would have to be quite poor - unless done intentionally for effect. Unless the loudspeaker presents a rather atrocious load, nfb will reflect little if anything of the loudspeaker load on the amp.
Yes. The 3rd harmonic will be at 21 kHz, inaudible. Unless such odd harmonics are generated in the super-audio band, that mutual intermodulation leaves strident products in the audio band. This is possible and real; at frequencies where this occur, the amplifier is no longer linear and in control. (That is why it is important for the designer to check his design to way beyond the audio band and where over-compensated transistor amps .... but I am off-topic.)
Jeepers.
I think of the Williamson amplifier with a frequency range of up to 300 kHz, Leak, Quad II and Mullard 5-20 also way up (power amplifer only) .....
I refurbished two ST70s a long time ago, but cannot remember things being that bad. H.f. response unregulated by nfb to the point that it falls inside the audible band ..... 😱
Reminds me of a Butler "Tube Driver" amp I once saw. I don't know the specifics of the circuit (and don't care) but it had a solid state amp section with a tube somewhere in the input. It also had a "Tube Sound" knob, which according to the marketing propaganda varied how much of the signal went through the tube. Turn it on, and sure enough there's that warm and inviting tube glow. (There's a reason that many higher-end restaurants have gone back to "Edison" style incandescent bulbs for their lighting!)
But guess what the "tube sound" knob actually controlled.
If your guess was something other than "a midrange EQ boost, as is typically what would happen with a low source impedance amp driving loudspeakers," well...you would simply be wrong.
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