audio-talk

As I promised Paul I would do, I've just lashed up a 6EM7 headphone amp, using the power valve section of the two dissimilar triodes as a single gain stage. I've used my other headphone amp as the test bed for the job:
IMG_0638.jpeg IMG_0637.jpeg
In the bottom picture, a Meanwell, 12V switch mode ...

I've bypassed the cathode resistor on the 12B4A.
There was a bit of residual hum between tracks with the cathode un-bypassed. That sort of noise drives me up the wall after a while with headphone amps. Some people will put up with it but it gets on my bleed'n wick!
A completely silent background ...

I've ramped up the HT by fitting a higher voltage, 150VA mains transformer.
So now we have more realistic voltages for the EL38s and the 12B4As.

Power supply and audio circuits below:

I now have single-triode, RCA 12B4As running at 11mA as the input stages: It was still slightly too loud with the ECC82s, but with the 12B4As, the gain is now just about spot-on.

Ouch!

Yep, it seems to be a success.

Back to the EL38 HPA and I've just introduced it to the RTZ DAC I got from Ray last year.
I mean, the sound is absolutely superb! This DAC brings out the excellence of the EL38 like none of my other DACs.
I can't believe how good this headphone system now is. It’s the best head-fi I’ve had to date ...

Yep

It’ll take quite a while to mod, but I’ll report back once I’ve got it sorted.

I can rig up my other headphone amp with 6EM7 if you're curious Paul

0.9W is incredibly loud on headphones.

Newest audio circuit:

A bit more work on the power supply and we're within 1V of the previous bias of 10.5V on the power tubes:

There was a bit of residual ripple in the earpieces of my phones, but a mod to the power supply sorted that one: Voltages are lower but there is no difference to the sound that I can hear. It's still fab.

Yep, they're bloody good valves! :D

I've solved the gain problem by using 1/2 an ECC82 per channel. It is fine now in terms of volume control travel.
I've wired the valves so that triode 1 of one envelope is active on the left channel and triode 2 of the other envelope is active on the right ...

I've gone triode on the input stage in an effort to reduce the gain, but there's going to have to be a rethink in that department in order to pull the gain down some more.
Nevertheless the sound is great. I can certainly see why Paul likes the sound of this valve.

And the PSU: