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Removed, wrong catagory. Was attempting to move over to 'Mods" and something went awry, trying to recover what I wrote, And thanks Loudthud for the info.
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Last edited by One10; Today, 08:43 AM. -
This might be a case of trying to do too much with too little. First step is to measure the gain (power amp input to speaker) with all feedback and bypass caps on the 2.2K disconnected. Next, measure the gain again with the 2.2K fully bypassed with something like 22uF. This will tell you how much boost you might expect with caps across the 2.2K. Lastly, connect feedback to the 100 Ohm resistor with the Presence control disconnected. The gain difference between the first measurement and this one will tell you how much boost the Presence control can give. Select the feedback resistor for numbers like 10X gain difference or 20dB are high, but not uncommon. That much gain reduction might be too much and cause the amp to oscillate.WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
REMEMBER: Everybody knows that smokin' ain't allowed in school ! -
It is often overlooked that adding global NFB lowers the power amp sensitivity.
So if the NFB lowers gain by a factor 5, the preamp needs to provide 5 times the input signal for full output.
If the preamp limits the signal at a lower level it might no longer be possible to achieve full clean output.
Could I see the schematic, please?- Own Opinions Only -Comment
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This Diagram of a negative feedback with presence control is what I was planning/hope to do, as a similar GA-8T had a 47k feedback resistor on the O.T. + speaker lead & originally was wired directly to pin 8 of the Cathode (V1B). I would also like a presence control, but it cannot work due the cathode bypass (larger) capacitors.
The reason I am attempting this is I do not like the amount of distortion this amp makes on 4-5 vol., or even only 2-3, I can hear it. I like clear. yes, that's right, I want a cleaner sounding amp. boo..hoo.. The presence control is to brighten the top end, as it is too dark (I believe it is due to the cannabis rex? speaker).
(Gibson wired V1A & ViB the opposite of what they show in their schematic, among other anomolies - that is why I hadn't included it and made a crude drawing instead.)
(I could not recover what I wrote previously.)
Last edited by One10; Today, 02:43 PM.Comment
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