On Sat, 13 Dec 2014 01:58:55 -0800 (PST), Phil Allison
wrote:


Jim Lesurf wrote:


The whole thing is a nonsense.

Damping Factor made more sense back in the days when power amps were
valve and almost all of them had high output impedances. But even then it
was a weird term given the details. e.g. Amps having an output impedance
that varies with frequency, level, etc, and generally *not* being
resistive. And speakers also being nothing much like a resistor. Alas we
seem stuck with the term.


** Damping factor has been relegated to a non issue with hi-fi amplifiers for many decades - despite which it still looms large in the minds of most audiophools. Bull**** baffles brains and good marketing gimmicks never die.

In another area of amplifier design, damping factors vary enormously from one model to another and yet rates no mention in advertising at all.

I am speaking of guitar amps, where the effective DF may be anything from 100 to 0.1 or lower - making for very audible differences.

Famous valve amps like Marshall and Fender have DFs of about 1 due to use of modest amounts of NFB. Early VOX amplifiers were class A and used no NFB at all resulting if very low DF numbers like 0.1. When VOX released their first SS models, the DF was even lower than the valve ones - due to using a combination of voltage and current feedback.

The same idea is still used in lot of modern SS guitar amps to get DFs of between 0.3 and 2, so mimicking the tonal character of popular valve models.

But makers keep it all a big secret.

How very odd.


.... Phil

Guitar amplifiers are a case apart. The maker does what is necessary
to get the sound he wants - fidelity doesn't come into it. He will use
low damping factors to encourage speaker resonances, that being part
of the overall instrument sound. That is why Celestion - pretty much
undisputed rulers of the guitar driver unit world - have so many
models with varying, highly resonant responses.

There was a lot of early resistance to SS guitar amps for this very
reason. Makers didn't really understand what was needed and tried to
adapt standard op-amp type circuits with a dominant pole and heavy
negative feedback. This was a failure on so many counts, from the
over-damped control of the speaker to the disastrously harsh limiting
characteristic that stopped people playing at high volume. This
resulted in the feeling that solid state watts were smaller than valve
watts.

In a decent valve guitar amp feedback is pretty much confined to the
taming of the wildly varying bias condition of the output valves. The
entire rest of the chain will be run open loop to achieve the desired
smoothly curving transfer characteristic.

d