-----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
like
the 6sn7, 37, 101, and the like. Transformer coupled, they produce very
low
distortion of any kind, can last 20,000 hours and have very few parts.
The
reason you don't see much transformer coupled designs like this is that
they
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
you're
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
problems
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
had
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
whistles.
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
when
you screw up digital.
Those field coil power supplies cost more than most transistor amps. The
permalloy and nickel cores are 'spensive!
Phillip
I wonder what some of you will think of this:
http://cygnus.ipal.org/mirror/www.passlabs.com/seclassa.htm
----- 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
>
>