This is a pedal-type distortion unit, which is a modification of the Mockman V2.0 by Runoffgroove (the name ReMock+ is a nod in the original’s direction, as well as a play on “remix”, with the “+” added to indicate the addition of an EQ).
Schematic:
What’s basically going on:
First off, definitely check out Runoffgroove’s page for the original circuit. While you’re there, check out some of the other circuits and info on offer, there’s some great stuff there.
The basic idea here is two cascaded, overdriven opamps. The opamps are configured to provide a huge amount of gain, such that the signal is clipped. The headroom before clipping in an opamp is set by the voltage of the opamp’s power supply– for example, an opamp powered by a +/-15V supply would have roughly 30V of headroom peak-to-peak, though it should be noted that many (perhaps most) opamps are not capable of “rail-to-rail” operation, meaning that actual headroom will be lower than the levels of the power rails. As with many opamp-based guitar effects intended for 9V operation, this circuit uses a trick known as a “virtual ground” to allow the opamp to operate from a single supply, but still have positive and negative swings in the waveform produced at the output. This is done by using a voltage divider on the 9V power input to give a 4.5V reference (or bias) voltage, which is then fed into certain parts of the circuit where the ground would be if the circuit was using a dual supply (in this case, the positive inputs of the opamps). This essentially makes the opamp see that 4.5V point as ground, and the actual battery/power supply ground as -4.5V, giving a (roughly) 4.5-volt swing in either direction. For more info on this and other aspects of opamp usage in guitar effects circuits, see this link at General Guitar Gadgets.
For this modification, I replaced the 47pF feedback capacitors with 100pF’s to reduce noise, and added a switchable 2-diode “softer drive” mod (the voltage drop of the diodes creates a softer clipping than just the overdriven opamp). I also added a 10k audio taper pot to the input, which allows for something approaching a clean signal, as well as control over the amount of clipping.
The second part of the circuit is a simple 2-band (hi/lo, or treble/bass) Baxandall EQ.
Old build notes here.
