Re: general question about audio amplifiers

From: Larry Brasfield (donotspam_larry_brasfield_at_hotmail.com)
Date: 03/13/05 

Date: Sat, 12 Mar 2005 18:10:45 -0800

"John Fields" <jfields@austininstruments.com> wrote in
 message news:jeu631hju37s1dj1kosn2j4m0dbm0lpons@4ax.com...
> On Thu, 10 Mar 2005 12:34:18 -0800, "Larry Brasfield"
> <donotspam_larry_brasfield@hotmail.com> wrote:
>
>>"John Fields" <jfields@austininstruments.com> wrote in message
>> news:m391311vv7s86u2i2jsv20jmmuu1set4fo@4ax.com...
>>> On Thu, 10 Mar 2005 09:47:54 -0800, "Larry Brasfield"
>>> <donotspam_larry_brasfield@hotmail.com> wrote:
>>>
>>>>What triggers my skepticism is the suggestion
>>>>that transformer transient response uniformly
>>>>tends to smooth output waveforms. I expect
>>>>that in the case of soft limiting, but I see little
>>>>reason to predict that the uneven phase response
>>>>of a transformer, together with the phase response
>>>>of whatever is done to preceeding stages to get
>>>>the magnitude response straightened out, will act
>>>>to produce smoother outputs.
>>> ---
>>> I'm not arguing "smoother", I'm arguing that some folks think tube
>>> sound sounds _better_ than transistor sound, whatever the reason.
>>> Perhaps it's because some of the crispy corners have been knocked off,
>>> perhaps because some of the edge rates have been slowed down, perhaps
>>> not. I don't know, but if they like it, so be it.
>>
>>
>>Just to help cultivate your sense of humility,
>>(and without suggesting it is lacking), I offer
>>this reconstructed sequence of our discussion:
>>
>>Q: Would, for example, the output waveforms be smoother on
>> a vacuum tube than they would be on a transistor amplifier?
>>
>>A(by LB): Only when the amp is underpowered for the signal
>> it is being asked to pass.
>>
>>S(by JF): Not 'only'. The transient response of the output
>> transformers has a lot to do with it as well.
>>
>>Q(by LB): Do you believe that, within the nearly linear output
>> range of a tube amp, the output transformer is usually going to
>> smooth out the content that a high fidelity amplifier would have
>> passed? If that is the basis of your contention, then I must
>> point out that transistor amplifiers can also act as low pass
>> filters, either intentionally (treble control) or not. If your
>> contention is not about frequency response, maybe you[r]
>> could explain your contradiction.
>>
>>R(by JF): [contrasting with magnitude frequency response]
>> The transient response, on the other hand, deals with the behavior
>> of the transformer when subjected to complex input signals and is
>> affected by, among other things, the leakage reactance and
>> interwinding capacitance in ways which wouldn't be readily
>> apparent when exciting the transformer with a single spectral line.
>>
>>R(by LB): What triggers my skepticism is the suggestion that
>> transformer transient response uniformly tends to smooth output
>> waveforms.
>>
>>R(by JF): I'm not arguing "smoother", I'm arguing that some folks
>> think tube sound sounds _better_ than transistor sound, whatever
>> the reason. Perhaps it's because some of the crispy corners have
>> been knocked off, perhaps because some of the edge rates have
>> been slowed down, perhaps not.
>>
>>At this point, I don't know whether we disagree or not. I have
>>to ignore parts of our discussion to take either position.
>
> ---
> You seem to think that a sense of humility is something which one
> should cultivate when communicating with you in order to allow your
> viewpoints to become dominant.

Actually, I think a sense of humility is a prequisite for
any competent but human engineer. And it is not a
bad thing for people generally to cultivate.

> I have no evidence, so far, that your
> intellectual prowess merits that kind of consideration.

The issue is not my prowess. The issue is how to
reconcile a set of inconsistent positions. I had
actually thought, incorrectly it seems, that you
would be able to see the inconsistency rather
than trying to bluster your way out. You could
take my prior post as a compliment.

> Just as an example, your statement that you'd have to ignore parts of
> our discussion belies the fact that, since the discussion has already
> occurred, no matter what you claim you can't ignore any part of it.

The fact is that you have come down on both sides
of the issue with respect to whether the frequency
response (which includes the transient response)
of a tube amp transformer will generally tend to
smooth waveforms presented to it. You initially
disagreed with my position on that, and later let
loose of your initial position, but have never quite
managed to acknowledge the change.

> Also, on sci.electronics.design you seem to be back-pedalling while
> trying to maintain your position as an authority about something.
> Anything...

I have never claimed to be an authority, so for
the sake of discussion, I will translate your
exaggeration into "have acted as if knew"
about something. ("Anything"?)

So, acknowledging an error is "back-pedalling"
and somehow inconsistent with believing oneself
to have relevant knowledge of some subject. I
suspect that view may explain a lot here.

> What might that be? We've seen nothing from you but idle chatter. No
> schematics, no math, not even verbal descriptions of circuitry, just
> half-baked opinions about how you think things should and shouldn't be
> done and why.

Funny, but I recall using the favored Ascii
schematic editor just so I could post a few
circuits here. And I've written enough
expressions to falsify your "no math" charge
unless you are trivially referring to some kind
of algebraic transformations all laid out. And
on several occasions, including a post today,
I have described the operation of portions of
a circuit.

> *** you and the horse you rode in on.

I cannot speak for the horse, but I decline, thanks.

So, did you or did you not contradict my claim
that output waveforms will be smoother from a
vacuum tube than they would be from a solid
state amp only when the amp is underpowered
for the signal it is being asked to pass?

And did you or did you not, after a discussion
about transformer transient response, finally
abandon the "smoother" position for tube amps
operating in their near linear output range? 

-- 
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
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