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    Building, troubleshooting and testing of these amplifiers should only be
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Adding headphone output to Darling amp

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Hi, I have a Darling amp (1626 tubes, 3/4 wpc output) and I added a headphone jack to it. 68Ω in series to each ear, and 10Ω across for crossfeed. The problem is, headphones have 3 conductors (common ground) but the amp has 4 outputs (each output transformer has two outputs) and the two negative outs definitely aren't internally connected, I tested that with a continuity tester. I simply shorted the grounds together, and it works, I get stereo sound out, but it sounds awfully flat and dull. If I break the shorted ground I get mono in both ears that sounds great, lively, but it's just one channel in both ears.

I guess I'm wondering, can a small single ended triode amp with output transformers even be used for headphones? If not, maybe that's why everyone uses OTL amps for headphones?

For testing, I find that "Don't Worry Baby" by the Beach Boys is great, it has a lot of hard panned vocals so you can really tell what's going on with stereo separation.
What is the purpose of the crossfeed resistor?

I use headphones with a tube amp all the time. In fact I started with a SE Darling amp. I just use the 4 ohm tap for headphones and speakers. Works perfectly with my phones (AKG K601). I don't use any extra resistors.
I guess was was thinking resistors in series are for attenuation, but with 3/4 wpc probably not needed. Tom McNally the guy I bought the amp from suggested 100Ω in series to each ear and 10Ω across. Let me try bypassing the series resistors. The crossfeed resistor seems necessary, otherwise you get hard panned stereo which I do find fatiguing.

One other thing, the sound I get out of the amp with point-to-point wiring and soldering is so much fuller sounding than the same circuit on a breadboard, not sure why that is. Maybe the breadboard provides cheap, noisy connections.
So forget what I said before, I had it all hooked up wrong. I think I was shorting the channels together for mono. The circuit I ended up with is simply 10Ω across the channels and 200Ω to each ear. Sounds sublime with Grado SR325is headphones. I tried different series resistors and more resistance gave it a fuller, bigger sound. It has that wonderful "toe tapping" quality. I'm quite satisfied. And it still gets plenty as loud as I'd ever need.
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