Been working on trying to increase the dampening factor of my tube amps,
without having to go the ultra regulated route. I've been doing a lot of
experimentation on St 70's since they are everywhere and still relatively
cheap (at least when I acquired my horde). Just passing on a tweak that
really seems to work well and greatly increases the control of the
amplifier, particularly in the deeper bass. I had been beefing up the bias
supplies with some performance gain, but the best performance gain was to
buffer the ground leg of the bias pot with a small capacitor, about 10 uF or
so, right across the resister that ties the leg to ground. Very cheap and
very effective.


Stu

On Thu, 10 Mar 2005 20:48:52 GMT, "audiodir"
wrote:

Been working on trying to increase the dampening factor of my tube amps,
without having to go the ultra regulated route. I've been doing a lot of
experimentation on St 70's since they are everywhere and still relatively
cheap (at least when I acquired my horde). Just passing on a tweak that
really seems to work well and greatly increases the control of the
amplifier, particularly in the deeper bass. I had been beefing up the bias
supplies with some performance gain, but the best performance gain was to
buffer the ground leg of the bias pot with a small capacitor, about 10 uF or
so, right across the resister that ties the leg to ground. Very cheap and
very effective.


Stu


I really don't understand how any of this changes the damping factor
of the amp, but do bear in mind that if you are doing stuff with small
value caps, deep bass is the place it will have *no* effect.

Can you give us some before and after damping factor measurements?

d

Pearce Consulting
http://www.pearce.uk.com

"Don Pearce" wrote

I really don't understand how any of this changes the damping
factor
of the amp, but do bear in mind that if you are doing stuff with
small
value caps, deep bass is the place it will have *no* effect.

Can you give us some before and after damping factor measurements?

I think he means quietening, like dampening the noise or hum. Stu,
the damping factor usually means the ratio of output impedance to
load impedance.

10uF in a high-impedance circuit like a fixed bias supply is not
small. Stu, watch you don't fry the valves by delaying the bias
voltage too much at power-up.

cheers, Ian

On Fri, 11 Mar 2005 01:32:17 GMT, "Ian Iveson"
wrote:

"Don Pearce" wrote

I really don't understand how any of this changes the damping
factor
of the amp, but do bear in mind that if you are doing stuff with
small
value caps, deep bass is the place it will have *no* effect.

Can you give us some before and after damping factor measurements?

I think he means quietening, like dampening the noise or hum. Stu,
the damping factor usually means the ratio of output impedance to
load impedance.

10uF in a high-impedance circuit like a fixed bias supply is not
small. Stu, watch you don't fry the valves by delaying the bias
voltage too much at power-up.

cheers, Ian


If he is modifying tube amps, I think we must start by assuming he
knows what the technical terms mean.

d

Pearce Consulting
http://www.pearce.uk.com

audiodir wrote:

Been working on trying to increase the dampening factor of my tube amps,
without having to go the ultra regulated route. I've been doing a lot of
experimentation on St 70's since they are everywhere and still relatively
cheap (at least when I acquired my horde). Just passing on a tweak that
really seems to work well and greatly increases the control of the
amplifier, particularly in the deeper bass. I had been beefing up the bias
supplies with some performance gain, but the best performance gain was to
buffer the ground leg of the bias pot with a small capacitor, about 10 uF or
so, right across the resister that ties the leg to ground. Very cheap and
very effective.

By dampening factor, do you mean the output resistance of the amplifier?

I have never noticed that voltage regulation ever improves the DF, and I can't
see
how placing a cap where you put it would improve the DF.
The DF, afaik is determined mainly by the amount of applied NFB in an ST70.
Its a UL amp, and without its global FB the Ro would be about equal
to the load value, maybe 8 ohms, so DF = approx 1.
But with 20 db of global NFB, DF is reduced to about 0.5 ohms or less.

Don't get me wrong, I am not against regulation. I also like good cap bypassing
where needed. I was just concerned at ppl's understanding of the concepts
you mentioned.

Patrick Turner.

..yebeout



Stu

"Don Pearce" wrote

If he is modifying tube amps, I think we must start by assuming he
knows what the technical terms mean.

Er...why? From the sense of it, I think we might be better warning
him not to electrocute himself...

Actually he said "dampening", not damping. I have given him the
benefit of doubt, considering he may be struggling with English.

Why have you asked for damping factor measurements?

cheers, Ian

On Fri, 11 Mar 2005 17:51:29 GMT, "Ian Iveson"
wrote:

"Don Pearce" wrote

If he is modifying tube amps, I think we must start by assuming he
knows what the technical terms mean.

Er...why? From the sense of it, I think we might be better warning
him not to electrocute himself...

Actually he said "dampening", not damping. I have given him the
benefit of doubt, considering he may be struggling with English.

Why have you asked for damping factor measurements?

cheers, Ian


Because he is talking about improving the damping factor. Measuring
the damping factor would seem to be a pretty fundamental part of that
exercise.

d

Pearce Consulting
http://www.pearce.uk.com