A Very Compact Tube Hybrid

This amp was born from the coincidence of two independent design efforts. One was cfcubed's efforts to make a teeny tiny hybrid amp as discussed on Headwize (now defunct). The other was my own background work on designing a hybrid that ran from a 24VAC wallwart but that would have a higher plate voltage like the SOHA II amp. I learned of cfcubed's thread when he wrote to me about using some of the design ideas in the SOHA amp in his Teeny Tiny amp. With a few emails we began work on this amp.

Features of the amp:

  1. Compact Tube Hybrid fitting on a 75mm X 120mm board (able to fit: Hammond 78mm X 120mm X 43mm case).
  2. No trimpots in front end. Rolling 12AU7 class tubes consists of turning off amp, pulling one tube & inserting another. Can be 6922 class tubes too (switch for 6.3V / 12.6V heated tubes). Many other tube types have also been found to work well (6F8G, 6CG7 6GU7).
  3. Runs tubes at 80V, about twice plate voltage of some other hybrids.
  4. Uses discrete output buffers, rail splitter, driving most all conventional/dynamic headphones with ease.
  5. Implements variation of AMB's e12 muting delay & offset protection (with red and green LEDs).
  6. DIYers can expect to be able to complete builds w/case, tubes & 24VAC 0.8A+ A/C adapter for under $200USD total.

I want to thank cfcubed for all of his great ideas, collaboration and time, and prototyping work.