The Fender Mini Twin Isn't Broken. It Was Designed This Way.

I bought this amp in London in the early 2000s because I thought it was the best-looking mini amp ever made. It is. It also sounded like a mosquito in a biscuit tin, and for twenty years I assumed that was just what you get for the money. Then I found a traced schematic, spent an evening with it, and realised the amp wasn't broken at all. It was doing exactly what it had been designed to do. Three things explain the whole sound: a single op-amp stage running a gain of 501, two silicon diodes hard-clipping everything into a square wave, and no speaker simulation whatsoever — so all the fizz that square wave generates goes straight to the drivers. Brian Wampler made a well-known video about this amp where he bypasses the preamp and the speakers entirely. It sounds great, but you're left with a small power amp in a tweed jacket. I wanted the opposite: same box, same knobs, same speakers, nothing visible changed. Just make it worth switching on. ── WHAT I CHANGED ── On the original board: R5 1k → 4k7 max gain 501 → 107 C5 470n → 1µF bass into the clipping: 340 Hz → 34 Hz D1/D2 2× 1N4148 → red LED vs 2× 1N4148 in series (asymmetrical) across C4 added 4k7 + 2× 1N4148 back to back (soft clipping) C20 47µF → 220µF cleaner preamp supply Volume pin 3 lifted — insert point for the cab sim Seven soldering jobs, none of them visible from outside, none of them irreversible. ── THE CAB SIM ── Built on a scrap of stripboard, 10 × 20 holes, hidden inside the cabinet. One 2N5088 as a buffer, one TL072 running two Sallen-Key low-pass cells. Cell A 33k · 33k · 6n6 · 220p 4.0 kHz, Q 2.74 → the presence bump Cell B 22k · 22k · 1n47 · 1n 6.0 kHz, Q 0.61 → the cliff Output 66n into 33k 72 Hz high-pass Supply 100R + 100µF The target was the Jensen P12N, the 12-inch speaker Fender actually fitted to the 5E8-A Twin in 1957. Result: +7.2 dB peak at 3.8 kHz, 70 Hz to 5.3 kHz at −3 dB, and 24 dB per octave above 6 kHz — which is what a real cone does. What I deliberately did NOT copy is the notch around 1.6 kHz in the published Jensen curve. That's a cone break-up mode measured on an IEC baffle with the mic straight on axis. Put the speaker in a cabinet and mic it off axis and it largely fills in. Copying the plot literally would have given me a hollow, telephone tone in the name of accuracy. A series resistor at the board input sets how hard you drive the filter. Pick it by ear. ── GEAR ── Guitar Fender Stratocaster Roadworn '60s Mic Shure SM57 Interface Focusrite Scarlett 18i8 Processing A touch of reverb, nothing else. No EQ, no amp sim, no post-processing on the amp sound. The reverb is only there because a guitar amp in a dead room doesn't sound like a guitar amp in a room. ── CREDITS ── Original schematic traced and drawn by DM, 12-23-2009, revised 8-3-2012. Without that document none of this happens. ── HONEST ENDING ── It does not sound like a Twin. It was never going to — the cabinet volume was never designed, it's a sealed box of a few litres with two 3-inch drivers and half a watt behind them. And to be fair to whoever drew this circuit, there was nothing Fender about it in the first place except the badge. It's an op-amp distortion pedal in a tweed box, closer to an MXR Distortion+ than to anything with valves in it. It's not a '57 Twin. It's finally a good little amp, which is all I wanted from it. #guitaramp #diyaudio #ampmod YouTube:    / riccardosolimena   Facebook:   / riccardosolimena   Instagram:   / rs24x7