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Just finished restoring a VTM 60 chassis. With a 1khz signal (200mV) into the amp I see a nice clean sinewave at V1 to V3 and at V4 the signal looks like a square wave with rounded edges all tone controls about the 12 o'clock position with presence at 10. Also assume that the "response modification" switches are off in the "up" position - that's where the switches are during this measurement. I haven't plugged in a guitar yet........I was expecting to get a pretty good sine waveform but not sure what the mod switches do even when assumed off.
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Look at the schematic.
The little switch unit should say ON or OFF right on it to indicate. And the panel names them.
Switch functions when ON:
Switches 1 and 2 add in a parallel cathode resistor or a bypass cap for V1b, affecting stage gain.
Switch 3 adds some clipper diodes across the input to the tone stack.
Switches 4 and 5 add in extra bypass caps for the cathode of V1a, affecting stage gain and low end response.
Switch 6 puts a cap in parallel with the tone stack treble cap for a mids boost.
Switches 7 and 8 add parallel caps to the presence cap to alter highs.
The owner manual from the Peavey web site has a reasonable explanation.
http://assets.peavey.com/literature/...s/80300704.pdf
This is a guitar amp, and I would not expect a clean sine wave through it. I am surprised it is clean all the way to the phase inverter as it is.Education is what you're left with after you have forgotten what you have learned. -
^^^^^^^^^^^^^^^^^^^^^^^What he said^^^^^^^^^^^^^^^^^^^^^^^^
Being a guitar amp, there are switches and parameter adjustments designed to intentionally get the amp into distortion. So the amp panel controls must be SET UP for a clean tone IN ORDER TO GET a clean tone. This requires a familiarity with the nature of modern guitar amps.
Sorry, I don't know what position is on or off for the DIP switches. Peavey IS a US company, and in the US we usually use "UP" as "ON".
Also, 200mV is a large signal. Maybe try the experiment again with 100mVLast edited by Chuck H; 08-31-2015, 02:13 PM."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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Agree and add: I bet the squarewave signal is about 60V RMS or thereabouts, I'm talking at the plate of course; after driving a tone control it will be attenuated.
And as Enzo said, the idea behind a tube amp is to distort, isn't it ?
Juan Manuel FaheyComment
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