Secret Variable NFB control on Mesa Amps

Looking at some of the Mesa amp schematics, there is the 'feature' of a slave output and a variable pot to control it's level.

Some amps (eg. Nomad), the Slave comes off an internal winding of the output transformer, and is not part of the NFB loop, so this would not apply to those amps.

On *some* of them (ie, the Heartbreaker), the Slave signal comes off the NFB loop, and has a resistor and pot in series with whatever theoretical load is plugged into the jack. The design likely presumes a high impedance load like a PA input or something like that.

However, if a very very low impedance load (or zero=shorting plug) is placed into the slave jack, a voltage (current) dividing circuit of similar magnitude to the NFB is created, and the slave output potentiometer then becomes a variable NFB control of sorts that should be able to reduce the negative feedback a great deal more than even what the bold switch accomplishes.

Cool?

Thoughts? Risks?

Can any amp techs on this forum validate this idea?

Well I don't know but it sounds interesting,I'm always into easy tricks. I'll be checking on this thread.

Calling Andy?

Apparently the Bold/Curvaceous switch is just for 2 different NFB settings so I'm not sure what this would add (besides continuous control of in-between settings). Still could be cool if it works...

It won't do anything detectable - even in those amps with the Slave driven from the same OT tap as the NFB. At best, even with a shorted plug in the Slave jack and the control maxed, you're shorting the NFB loop to ground via a 10K resistor (in the Heartbreaker, maybe different in other models but it won't be massively so), which is so high relative to the source impedance of the OT winding that it will have no effect.

It can't do any harm to try though, just in case it does have some very small effect that I'm overlooking.

94Tremoverb said:

It won't do anything detectable - even in those amps with the Slave driven from the same OT tap as the NFB. At best, even with a shorted plug in the Slave jack and the control maxed, you're shorting the NFB loop to ground via a 10K resistor (in the Heartbreaker, maybe different in other models but it won't be massively so), which is so high relative to the source impedance of the OT winding that it will have no effect.

It can't do any harm to try though, just in case it does have some very small effect that I'm overlooking.

Click to expand...

It would be interesting to know how much current gets delivered into the NFB circuit by the OT.

That would give us a relative idea on how much could be drained away via the dividing network set up with a shorting plug, correct?