• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Bassman aa864 master volume mod

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If it is after the phase splitter, you will need a tandem pot and two sets of screened lead.
Not advisable!!!
Place the pot on pin 2 of the phase splitter ECC81, use a 1M pot, in place of the 1M grid leak resistor, and a 10k grid stopper on pin 2 to the wiper of the pot. The feed end is your 500pF capacitor and the cold end is chassis.


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This is the schematic:
Master-Volume — imgbb.com
The question is:
I can use this XLR cable? or I need to separate cables with his own shield?

1) that PPIMV works fine.

2) you can use a single shield around both wires.
In fact, unless you are extremely sloppy (I guess not :)) you don´t even need a shield there: signal level is around 50V RMS or higher :rolleyes:

as of:
It will introduce distortion as the impedances vary and possibly go unstable.
it´s a plain vanilla Volume control, used by the trillions around the Worls since forever, just placed between PI and powern tube grids.
Why would this one create unstability while others do not is a mystery to me.:rolleyes:

But then I am not the best Engineer in the World like some posters here.

As of:
Why do you think that the manufacturers never used your proposed system?
You mean Fender?
Well, ummmmm, ..... because they designed a **clean** amplifier and weren´t interested in .... ummmm ..... distorting it?

Or, God Forbid .... losing Headroom? :cool:

As of the MV suggested in post #4 , it is a standard MV placed between preamp and power amp, and in a classic Fender amp is very very very hard to clip.
As in some 20/30 dB harder, go figure.
Some random thoughts:

  • Best engineers in the world? Fender Musical Instrument? Really?:D
  • The bassman 5F6 circuit is often wrongly connected to the Western Electric patent: WE used a paraphase inverter, Fender uses a Long Tail Pair, big difference.
  • With that said, the 5F6 circuit is the ultimate one: any amps that matter use it, from Marshall to Dumble, and most anything in between.
  • An instrument amp is part of creation, not reproduction; what seems to be heresy in a HiFi amp may work fine in a guitar amp. If you have the means to try a master volume after the phase inverter, go ahead and do it, and tell us what you think. I'm pretty sure the tone is more complex than a MV before the PI.
  • Personally, I prefer an even more complex tone by overdriving the output stage also. I simply use an attenuator between the amp and the speakers.
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