SWR-Style Bass Limiter

A few years ago I was given a couple of rackmount bass preamps to fix (a Groove-Tube Studio 220 and a SWR bass preamp) and also two SWR Bass amplifier, one head one combo ... turns out the front-end on all four units was near identical, the design of Steve W. Rabe ... Mr. SWR is a well-known industry person, he was on the Acoustic Control design team, and reputed to have tweaked the fuzz circuits in Jaco's 360's ... how I would love to have tea with this person !

Groove-Tube "Studio 220" pdf

I became especially curious about the one-knob limiter circuit after fixing and playing these units ... I thought the circuit worked pretty well for bass so, as an exercise, I adapted that portion of the SWR pre-amp circuit into a low-draw dual 9 volt circuit ...

1'st SWR-style Limiter schematic

Later I came up with the idea of adding two parametric filter stages at the input of the side-chain circuit ... this way I can boost or cut the sensitivity at the bottom end and top end of an E-string bass neck (at 50Hz and 190Hz roughly) ... when dialed at 12 o'clock the response there is flat - providing stock SWR side-chain response ...

Parametric SWR-style Limiter schematic

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