Re: Happy St Patrick's Day, Boss!

John Byrns wrote:

>  Eeyore <rabbitsfriendsandrelations@[EMAIL PROTECTED]
> wrote:
> > Iain Churches wrote:
> >
> > > However, there are difficulties in tube amplifiers,
> > > which I am told, one does not encounter in SS
> > > amps as they do not have an OPT. Have you
> > > ever tried to apply the optimum of NFB in a
> > > tube amp while keeping a good stability margin
> > > into say 0.22µF ?
> >
> > Well .... since no normal speaker is represented meaningfully by a
0.22uF
> > load, I'd probably not over worry about that.
> >
> > Of course, one would first tend to 'isolate' that 0.22uF by means of a
small
> > value output inductor in the case of the solid-state amp. In the case
of a
> > tube amp, the leakage inductance of the OPT will do something broadly
similar.
> > Of course, one then needs to be totally in control of the OPT design.
>
> 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
!

This is done obviously to help reduce the horrible distortions introduced
by the
OPT.

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.


>  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
?


Graham