Chuck D. Bones
Circuit Wizard
A few weeks ago, MattG asked if it would be possible to replace the CD4007 OD's JFET front-end with an opamp. That sent me down the proverbial rabbit hole and this is what (eventually) popped out. First stage is an opamp 18dB clean boost. Second stage is a variable-gain CMOS amplifier. Third stage is a Catalinbread VariOboost, with slighty-altered component values. Fourth and fifth stages are the same variable gain stages used in the original design, with a few component value changes. At the end is a BMP-style tone control followed by a volume control.
Seven knobs
PREAMP sets the 2nd stage gain.
BASS is a variable freq bass rolloff based on the Friedman TIGHT control. It's located near the front of the signal chain, ahead of the distortion stages.
MID & MID FREQ are the familiar VariOboost controls. VR5 is a dual-gang C100K.
TREBLE is a passive high freq cut / boost, using the familiar BMP tone circuit. It's located at the end of the signal chain, after all of the distortion stages.
MASTER sets the 4th & 5th stage gains.
LEVEL is the usual volume control.
With PREAMP & MASTER dialed-down, it's a clean boost. Turning PREAMP up gradually adds dirt before the Mid controls. Turning MASTER up adds dirt after the Mid controls.
So far, it only exists as a Breadboard. I'm pretty happy with it as-is. The most I'd change at this point, if anything, would be a couple of component values. Total gain at the output of the 5th stage is a healthy 72dB with the MID controls set to noon and everything else dimed.
Seven knobs
PREAMP sets the 2nd stage gain.
BASS is a variable freq bass rolloff based on the Friedman TIGHT control. It's located near the front of the signal chain, ahead of the distortion stages.
MID & MID FREQ are the familiar VariOboost controls. VR5 is a dual-gang C100K.
TREBLE is a passive high freq cut / boost, using the familiar BMP tone circuit. It's located at the end of the signal chain, after all of the distortion stages.
MASTER sets the 4th & 5th stage gains.
LEVEL is the usual volume control.
With PREAMP & MASTER dialed-down, it's a clean boost. Turning PREAMP up gradually adds dirt before the Mid controls. Turning MASTER up adds dirt after the Mid controls.
So far, it only exists as a Breadboard. I'm pretty happy with it as-is. The most I'd change at this point, if anything, would be a couple of component values. Total gain at the output of the 5th stage is a healthy 72dB with the MID controls set to noon and everything else dimed.
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