Master Volume Noise

[steveneddy]

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[Jana]

Post a schematic of what you have.

You may also want to check things out with a scope and see what is going on. You may have an oscillation that is out of hearing range. In effect, your master and presence are acting as "radio tuners" at certain settings.

[steveneddy]

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[Jana]

The first error I see is you can't take the signal off of the plate of V2b. There is no signal there.

[steveneddy]

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[Jana]

The first schematic you posted is not the same as the second one. The first looks like you took a standard 5F6A circuit and moved the tone stack but left the cathode follower. You CANNOT take the signal off of the plate of the follower--it is tied to B+.

The second schematic is a chunk of a trainwreck. What is it you want to do with that?

Who is "we"?

[steveneddy]

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[steveneddy]

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[Jana]

You're an "amp designer", right? You make and sell amps, right? Deadwood Amps, if I recall correctly.

I congratulate you, you had me going and totally punked me.

[steveneddy]

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[John_P_WI]

Jana is correct as usual. What she is referring to is that in your first scheme, as it was drawn the signal is taken from the plate directly tied to B+, which is the same as a "signal or ac ground".

The trainwreck scheme shown has the signal taken off between the 100k connected to B+ and the plate.

The current flow through the resistor (100k in the trainwreck scheme) causes the signal voltage. The resistor is not present in the first "plate loaded" scheme.

Got it? Fundamentals and physics.

[JazzGuitarGimp]

The first place I would look is at the 22nF cap feeding the CW terminal of the MV pot. If it's leaking DC, you'll have scratchy noises on the MV pot.

Then have a look at the 22nF cap between the wiper terminal of the MV and the input of the PI. Check it for DC leakage as well.

The easier place to start is try measuring for DC voltage at the CW terminal of the MV pot with the amp at idle.

[JazzGuitarGimp]

Also, Jana's original suggestion about scoping for oscillation is right on. I would start by scoping one of the outputs of the PI because the additional capacitance from the scope probe directly on the PI input could cause the oscillation to stop.

BTW, I almost didn't respond to your post: Your arrogance toward Jana, who was only trying to help you, was a bit over the top. Best of luck to you.

[steveneddy]

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[JazzGuitarGimp]

I know a lot of people believe when you start a sentence with "with all due respect", that the speaker is expressing genuine respect for the listener. And that was probably true a hundred years ago...

Your first hand drawing will not work. You cannot get signal from the B+ rail any more than you can get blood from a turnip.

Skipping over the Trainwreck schematic to your second hand drawing: this will work. When you have a large resistor in the cathode, and no resistor in the anode, it's called a Cathode Follower, and signal must be taken from the cathode. There is no (or at least, very little) signal to be had from the anode.

If you believe your circuit is wired according to the first drawing, and you are getting signal at the output, then your circuit is not wired per the schematic. Plain and simple.

If you do have an oscillation, and you are sure the circuit is wired correctly, then the issue will most likely end up being lead dress.