Hey folks! I’m trying to design a 1 watt guitar amp with quasi-complementary output, using a 12v supply. The quick sketch below is partly inspired by the Leak 30, as well as a book by Teemu Kyttälä on solid state amps, and some other reading. Not shown is the gm-compensated mirror on the preamp side.

My questions are as follows:

  • do you think 12v is adequate for this circuit?
  • is there anything that’s just plain wrong here? Yes, it looks crude/simple, though I’m mostly asking whether I’m going to fry something.
  • would it be worth my while adding a Zobel network at the output? I don’t mind some dampening if the ends are justified.

This is a small guitar amp I want to use in my apartment; No more than a single watt is required. And I’m looking for an American-style sound with good distortion at the higher end.

Thanks in advance :)

  • bitcrushedCyborg@alien.topBEnglish
    1·
    10 months ago

    With an efficient and well designed output stage, 12V should probably be able to get you close to a watt of peak power through an 8 ohm speaker. Some suggestions/criticisms:

    1. Add another coupling capacitor between the volume pot and the first transistor to prevent popping when you change the volume.

    2. Something doesn’t look right with the right half of the schematic. You have wires jumping over stuff, just to end up being connected to the points they jump over. The output transistors’ bases are shorted together, as are the two outputs from the preamp. R3&R5 are in parallel, as are R4&R6. I’d suggest checking out examples of class B push-pull amplifier and class AB amplifier circuits to see what to do.

    3. You’ll probably want some way to minimize crossover distortion from the output stage. Look at class AB amplifiers for examples of how.

    4. Simulate it so you can thoroughly test everything. CircuitJS for quick and easy, LTSpice for detail and accuracy.

    • coffeecalmsmedown@alien.topOPBEnglish
      1·
      10 months ago

      Hey thanks, I’m going to work on it a bit more today and post the whole circuit, input stage and edits included.

      I’m kind of stuck on quasi-complementary output for now, though maybe an AB amp would be a good design for afterwards. The Leak 30 Stereo, Mullard 5-10(tube), El Cheapo, Armstrong 600, and the Sinclair Z50 all used quasi-complementary output, and I’d really like to try to get a less-modern sound, if that makes sense. More to come!