A project log for Keritech "Little Red Devil" Single-Ended EL84 Amp

A single-ended tube stereo amplifier with a modern technology twist

keri-szafirKeri Szafir 01/01/2023 at 22:580 Comments

I built this amp on an extremely limited budget, having to make do with what I had in my lab (vintage parts), the cables, connectors, audio pot and enclosure from my customer, and secondhand vintage output transformers. He once mentioned he'd be tempted to make it red... while I already had painted the enclosure. Great minds think alike, it seems. I decided to make an amp that not only sounds nice, but also looks lovely, that's why I went to extra lengths with the internal construction to make as few holes in the enclosure as possible, and used an extra box to house the output transformers and control circuit board. While the pot control and Bluetooth interface were customer's wishes, I treated them as an additional engineering challenge, looked into doing that and I did... An interesting additional challenge for me - to avoid drilling holes in the enclosure, but still have a possibility of adding a remote (which normally would be done by putting a jumper on for powering up the controller), I used a reed switch from an old telecom relay. Putting a magnet over it before switching the amp on will throw the microcontroller in the programming mode, allowing the user to define the remote control buttons for volume up, volume down and input selection.

After several months of coping with depression and anxiety, which means I rarely had energy to go on and my progress slowed, I finished the build, tested and debugged it, put it together, drew the schematics and made documentation, YT video included :).