Re: Happy St Patrick's Day, Boss!

"John Byrns" <byrnsj@[EMAIL PROTECTED]
> wrote in message
news:byrnsj-74F5B9.18260819032008@[EMAIL PROTECTED]
> In article <47E19032.BAFB6F9@[EMAIL PROTECTED]
>,
> Eeyore <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote:

>>> I thought that in a typical tube audio amplifier, with
>>> NFB taken from the speaker terminals, that the leakage
>>> inductance of the OPT increased the total phase ****ft,
>>> making the stability problem worse rather than helping?

>> Well ..... if you insist on taking the NFB from that
>> point in the circuit !

> Well..... I don't insist on taking the NFB from that
> point, given my druthers I would take the NFB from a
> tertiary winding.

Seems suboptimal.

> However using a tertiary winding for
> the NFB doesn't give a competitive number for the spec
> sheet, although the DF so obtained is more than high
> enough for driving a speaker system.  A commercial
> compromise would be to take the low frequency feedback
> from the speaker winding, and the high frequency feedback
> from a tertiary winding, combining the two feedback
> signals in a sort of reverse crossover network.
>
>> This is done obviously to help reduce the horrible
>> distortions introduced by the
>> OPT.

Agreed.

>> Since an solid-state amp doesn't have this miserable
>> distorting lump of iron in the
>> way, NFB is taken BEFORE such a network. That's how we
>> can get THDs in the  0.001%
>> region.

> But do THD numbers that low actually serve any useful
> purpose, i.e. better sound, other than fueling the
> engineers ego, and making impressive numbers to put on
> the spec sheet?

Yes, improving THD below 0.01% is pretty futile. However the problems of 
tubed amps are one or more orders of magnitude larger.

>>>  For the leakage inductance to be helpful in the way you
>>> suggest I would think that the negative feedback would
>>> have to be taken from either the primary of the OPT, or
>>> from a special tertiary winding on the OPT.  Don't
>>> solid-state amps take the negative feedback from a
>>> point prior to the "output inductor"?

>> They DO, for very good reasons. See above.

>> Why are you chained to a flawed method of amplification.
>> Tube based amplifiers are
>> inherently HIGH distortion. Why not accept that fact and
>> be happy with it ?

> We are all chained to flawed methods of amplification;

Yes, but here's a news flash you seem to badly need, John:

The magnitude of the flaws affect their relevance.

> even solid-state amplifiers are flawed.

Even if they are commonly an order or three magnitudes smaller. That does 
make a difference!

>  I readily accept
> that tube amplifiers generally have higher distortion
> than solid-state amplifiers have,

And as flawed as many tubed amps are, it makes an audible difference.

> I don't believe I have
> ever claimed otherwise, unless it was in jest.  However,
> tube amplifiers are capable of sufficiently low
> distortion such that their distortion contribution in
> high fidelity audio systems is low enough to be
> irrelevant.

Only with great additional expense and inconvenience. It's the cost and 
inconvenience that attracts many.