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Simple idea for a 12AX7 boost/OD, some help needed to finalize:

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  • Simple idea for a 12AX7 boost/OD, some help needed to finalize:

    Still just a little sparkle in my head but I noticed that the torroidal transformer in my little Madamp G2 amp is fairly small. The primary is 230V (for Europe) and secondaries 6.3 (heater) and 185V (plate).
    Now 185V is a little above average for a 12AX7, so it'll run with a lot of headroom. Right there would have a footswitchable or switchable resistor to change this.
    We could have a drive pot after the first triode, and a level after the second. Though the drive would influence the level a lot so both would be highly interactive.
    Switchable bias resistors for the triodes.

    It'd have to remain simple but versatile. Mostly an extra gain stage, a real boost from a genuine tube. But above all, a fun and educative project mostly for me.

    Now the questions... Does the classic 68K resistor still need to be there at the input? These frequencies would normally be taken care of by the same resistor in the amp, but since they'd be amplified by the pedal, getting rid of them earlier may improve the sound quality?
    Also, assuming a very straightforward unit with a minimum of parts, would there be a huge level boost between input and output, or would it be properly controllable via a correct 'level' pot?
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