This is a rare one from the early 90s from Way Huge and is based on the Craig Anderton Frequency Booster. Stock it gives a mid range boost (800Hz), but that frequency can be altered by swapping the 2, 22nF caps:
220nF – 90Hz (lows)
100nF – 200Hz (low mids)
10nF – 2kHz (mids)
4.7nF – 4kHz (upper mids)
