In reality a simple stop box design with added LED meters for input and output. As it turns out they are not that useful as I like the way EC400 compress when pushed hard. Which are tuned by ears, not eyes. Op-amp used here are the JRC4558D made famous in the guitar community by TS808 Tube Screamer.
My unit had at some time been modified to interface with consumer gear, maybe to fit a DJ setup. I removed these phono connectors and fixed ground loop using isolated jacks. Added a prototype PCB with two fuses, inserted on the secondary windings of the transformer to comply with local regulation for mains voltage.
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