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In Reply to: RE: 3B SST... posted by Disbeliever on April 9, 2014 at 02:26:41:
No need for the condescension. Maybe you guys have learned something during all your years of "experience" but based Disbelievers amps of choice I am inclined not to think so. Experience is not a substitute for talent.
As for the linearity of devices there is no debate, triodes are more linear than bipolar transistors by a long way. So are FETs for that matter...at least running Class A. Adding more non-linear devices in a circuit doesn't make the circuit more linear, it makes it less so. This is only logical and it can also be shown easily if you build any kind of circuit with them and don't wrap it up in negative feedback...fact is that if you go with multiple stages you MUST use some negative feedback and often it won't be stable without it. At least with a FET or SIT you can take one, run it Class A and it will be stable, sound very good and measure ok to a few watts. With a tube amp you need probably at least two stages but the whole thing will run without feedback and still measure ok and sound really good as long as you used good parts.
Making an amp with multiple stages (this is also true for FETS or tubes) only makes it less linear and then NECESSITATING the use of local and/or global feedback just to control the way too high gain and stability issues.
"essentially within the realms of current negative feedback" Heard amps with this topography like Accuphase and well YAWN, they didn't sound very good despite the glowing press...They sound gray and dead.
"believing as you do that an amp with limited distortion sounded better" Their problem is the same as others, the use of the wrong design gives a poor sound not the absolute amount of distortion. The design dictates what the form of that distortion will be and it is that pattern that is important. Find the design parameters that deliver the right pattern and you get good sound...stray into ultra low distortion techniques and you pay in sound quality. It is not as you think that it is because the distortion is low it is because of what was done to the signal to get it low that is the problem.
"Referring to Geddes and Lee have you considered what happens when when say an audio amplifier of the transistor variety uses differing devices throughout the amplifying stages , for instance a J.Fet front end with it,s slope character followed by a standard B.polar VAS stage then followed by by say Mosfets, here you have three different slopes all adding their own particular distortions , feed all these back into the early stage and you have a disparity of control which results in both odd and even harmonics but more importantly some of the harmonic intervals are not amplitude consistant meaning some harmonics in the higher reaches have a larger than those proceeding, perhaps this is one reason why feedback can have rather unpleasant sounds with some designs"
Once you have multiple stages and complex topologies in each stage AND feed all that back to the input I don't think it matters anymore what the elements are. Especially if one of the stages is Class B. Like I said, a tube push/pull amp in Class AB that is not triode and uses negative feedback will suffer many of the same problems because a non-triode tube is also highly non-linear, feedback exacerbates the problem AND it is likely to have transformer saturation issues unless the output iron is very good. I don't cut them any more slack than most transistor designs.
I have found that one thing that works very well is a hybrid design with two stages only, running Class A or very high bias AB (so like Class A 10 or more watts). With a FET output this can be run without any feedback and will sound very good with low absolute and low order distortion primarily. Make this single ended and it will sound even better but the amp will have to be physically huge.
Of course the pure tube variant and reverse hybrids (like KR Audio) can also sound phenomenal.
"I simply believe that a properly designed Transistor amplifier will give very satisfactory and pleasing results and can be blameless,"
And I would simply argue that no such animal exists or has ever existed, nor will exist until a truly linear amplification device is invented. Until that device is invented then I will stay with the psychoacoustically correct path for sound reproduction.
I also don't really care too much what engineers think on these matters...they are usually designing by what they learned is proper circuit design and to price points for the market. The majority of them are not scientists and don't know how to make the proper observations about what their products are doing. I am a scientist, which makes me a professional observer, which means i hear things in their products that they don't or wish not to hear. I may or may not know how to design various cool and tricky circuits but I know how to tell when one is doing the right thing and one is not. THen I bother to find out what was used and how it was implemented and wait to see other similar examples and how they sound. One can build a mental library of what sounds consistently good and what doesn't and start to draw conclusions about various "innovations" in circuits. I have done so and came up with some guidelines for a good sounding amp. I would share them with you but I doubt you would take them seriously. I have posted them before so feel free to search under my name and you might find my ideas.
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Follow Ups
- RE: 3B SST... - morricab 14:27:29 04/09/14 (0)
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