Re: [ARSCLIST] Stereo records.

[Scott Phillips <scottp@xxxxxxxxx>]

One might point out that since the field coils in the speakers were used
as 'chokes' in the power supply, the increased current drawn through
them at high output levels changes the amount of magnetic flux available
in the speaker. This would add yet another dimension to the 'tube sound'
when overdriven...

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx] On Behalf Of phillip holmes
Sent: Tuesday, June 20, 2006 1:42 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
>
>