I’m moving discussion of the Darkvoice 336 to this tube amp thread. I’m messing around with the 336SE right now, and it’s best described as odd and funky. The sound quality can be decent, but you must do your homework and go in with your eyes open. It’s best suited for experimenters, or at least not purchased as a general purpose amp.
Compatibility: This OTL amp is best suited for 300 or 600 ohm impedance headphones. The sound is fine when one hits on the right tube/headphone combo, but it’s not intended for all headphones (e.g., not low impedance products from Focal, Dan Clark, etc.)
Feed speakers as a preamp: It has a line out and can work with your speaker amp. Some DIY people believe this degrades the sound and remove the internal wiring. I can’t comment either way.
Hum Issue: Yes, the 110 volt version hums like mad with some tubes. The Darkvoice seems to be the least compatible with Russian tubes (e.g., Foton, modern Tung-Sol). Mine is quiet with the bundled Chinese tube and Sylvania tubes. Some people advocate 72 hours of burn-in with new tubes while others modify the electronics. There are several standard modification processes.
Volume Pot: The usable range is tiny – just from 7 o’clock to 8 o’clock in my case. Some swap the pot while others use a preamp to feed it.
Power Switch: It’s long and thin and fragile. Some choose to swap it while it breaks for others.