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Re: [ARSCLIST] Stereo records.
Tube amplifiers using output transformers are quite limited as to the amount
of negative feedback because of significant phase shift introduced by the
transformer at both very low and very high audio frequencies. Instability
can occur with moderate amounts of feedback. Output transformer cores can
also saturate. Both limitations result in higher distortion for tube
amplifiers as compared to solid state amps, both using negative feedback
levels that are essential to achieving high performance.
Media Sciences, Inc.
> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:ARSCLIST@xxxxxxx] On Behalf Of phillip holmes
> Sent: Tuesday, June 20, 2006 2:42 PM
> To: ARSCLIST@xxxxxxxxxxxxxxxx
> Subject: Re: [ARSCLIST] Stereo records.
> Several reputable engineers have proven that a triode tube is inherently
> more linear than a transistor. That is, a triode is much more acceptable
> without feedback than a transistor without feedback. They tested tubes
> the 6sn7, 37, 101, and the like. Transformer coupled, they produce very
> distortion of any kind, can last 20,000 hours and have very few parts.
> reason you don't see much transformer coupled designs like this is that
> were very expensive to build. Good input and interstage transformers have
> always been hard to produce. But that doesn't mean in the real world
> going to use archaic single ended circuits with zero feedback.
> Tubes produce more even order harmonic distortion. On the other hand, if
> you have push-pull tubes, the even order harmonic distortion is often
> canceled out more than the odd harmonic distortion, subjectively a less
> pleasing sound. Psychoacoustic research has shown that people will accept
> even ordered distortion much more so than odd ordered harmonics. I don't
> much mind harmonic distortion as much as IM/TIM distortion and the
> associated with too much overall loop feedback. I've heard class A single
> ended transistor amps that sound like tube amps (but with drive!). They
> zero feedback, fewer stages, and predominantly 2nd, 3rd and 4th harmonic
> distortion. The measured harmonic distortion was close to .5%, but
> SUBJECTIVELY, the sound was cleaner than that of the transistor amp with
> more stages, tons of feedback, push-pull complimentary, bells and
> I think the single ended class A transistor amp also clips and compresses
> more naturally than does a complicated amp. Feedback can only do so much
> before it falls apart. With a simple circuit, it just compresses and
> saturates. But none of this can hold a candle to the awful distortion
> you screw up digital.
> Those field coil power supplies cost more than most transistor amps. The
> permalloy and nickel cores are 'spensive!
> I wonder what some of you will think of this:
> ----- Original Message -----
> From: "steven c" > Two thoughts...
> > 1) The whole point of using tube amplifiers is the fact that what
> > distortion
> > they do create is much more pleasant to listen to than the distortion
> > of solid-state amplifiers (in fact, it may be that tube amps need to
> > be driven slightly into distortion to produce their desired sound!).
> > As a blues harmonica player, I WANT an overdriven, distorted sound...
> > and, as a result, have to use small tube amps (I can overdrive my
> > only solid-state amp, but the results grate on my nerves!). I would
> > assume this is because an overdriven tube amp produces a distorted
> > waveform, but NOT one resembling a square wave (tubes approach
> > cut-off gradually)...while an overdriven tranistor simply goes
> > so far and no farther, producing pseudo-square wave output?!
> > 2) It would seem to me that if field coils are being used as they
> > once were (they were also the filter chokes for the B+ supply)...
> > using them would lead to problems with audible hum? Of course, for
> > $15,000 they could afford to provide a filtered-DC supply for the
> > field coil(s)...
> > Steven C. Barr