Here's the Hot Tubes overdrive from Electro Harmonix. It's based around a 4049 hex inverter chip (like a Red Llama) with a dual op amp pushing it. Original units from the 70s had buffered bypass and a direct out jack. I guess they needed something to fill up those massive enclosures EHX used back in the day. I've laid this out for a 125B enclosure with top mounted jacks and your favorite method of true bypass switching.
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