Valve Headphone Amp

[simon]

I've got a Spice model working for a ECX10N20 MOFO. It might even be something like accurate. Or not. Set up at 20V Vdd and 4A through the ECX10N20 and choke.
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Zen2 20V 4A MOFO circuit.png (98.71 KiB) Viewed 28759 times

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AC analysis. Interestingly it looks like gain of the buffer is x0.9, a bit lower than I might have expected.

Zen2 20V 4A MOFO AC.png (123.53 KiB) Viewed 28759 times

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Transient analysis with an input voltage of 10V. I reckon by 12V it's clipping at the top of the wave. Purple is the input signal, green the output.

Zen2 20V 4A MOFO transient.png (117.75 KiB) Viewed 28759 times

[Nick]

AC analysis. Interestingly it looks like gain of the buffer is x0.9, a bit lower than I might have expected.

Seems about right into a 8 ohm load. Current gain of course is much higher than 1

[simon]

Yep. If I get chance tonight I've have a look at the OP to see what happens if I "reduce" it to accommodate the relatively low swing of the potential input.

[simon]

Another thread that's probably in the wrong sub-forum now. What started out as a valve headphone amp morphed into a MOSFET source follower headphone amp, and is now a MOFO style power amp.

I thought I'd build the Zenductor 2 mentioned earlier in this thread. For a simple amp it's taken rather longer than I expected but that's life. I used Cinemag AVCs rather than the cheap Triads in the original. Overall I'm still weighing it up but I must say the simplicity of AVC gain stage and MOSFET source follower output stage has a beguiling clarity and detail that surprised me. I haven't switched back to the 45SET yet but it does seem less coloured, if a little short on gain. Perhaps this is the benefit of reduced distortion? Dunno.

It's perhaps a little on the lean side soundwise, but I'm still weighing it all up. It's making me revisit the MoFo, which still needs rebuilding. All very interesting.