6V6 Headphone Amp

[Cressy Snr]

Thought I'd put this here, now that the 6V6 SE has become a headphone amp.
The stereo 6.3mm, TRS jack socket is due to arrive tomorrow, so I'll be able to get it going properly without a mess of clip leads poking out the front.

In the meantime here is the audio circuit schematic:

6V6HPA.png (58.31 KiB) Viewed 72808 times

[Cressy Snr]

And the power supply:

HPAPSU.png (89.55 KiB) Viewed 72806 times

With a 5R4GY rectifier, the output valves dissipate 11.3W. Maximum anode dissipation is 12W.

[Cressy Snr]

Job’s all done now after fitting a Neutrik, locking 6.3mm headphone socket.

IMG_0468.jpeg (173.76 KiB) Viewed 72748 times

IMG_0470.jpeg (121.54 KiB) Viewed 72748 times

Transition complete.

[jack]

Lovely!

[Cressy Snr]

Cheers Nick,
it would have been a shame to have left this amp gathering dust upstairs. I don’t know where the idea of a headphone amp came from, it just hit me from nowhere last week. I could get well into Head-Fi, given the sound quality on offer from a good pair of phones and a tube headphone amp.

[Cressy Snr]

Quite a lot happened last week, in head-fi land.

It started when the last 6SN7 that was any good for headphones, started to become increasingly noisy and microphonic. The offending valve was a used Italian Fivre job from the 1960s with a broken centre spigot. The deterioration of this particular tube left me in a bit of a bind as there was nothing else octal in my boxes that would work.

Mr I had sent me a couple of Soviet 6SN7s but unfortunately they proved to be too microphonic for a headphone amp, which was a pity, as they are good sounding valves in the context of a 'normal' amp.

I finished up having to completely re-think the input stage. There were a few more valves in the stash sent by Mr I that looked promising; these included a pair of 6N6P, a pair of 6N1P and a pair of JJ ECC99. I also had a couple of EH 6H30Pi of my own. I thought that apart from the 6N1P (too high gain) the rest of these might be good choices for the input stage for the headphone amp, providing they were not going to be microphonic.

After a few days of cursing, making up adapters, fitting and soldering up 9 pin socket in place of the octal, I tried the 6H30, and the 6N6P as used in the Little Dot HPA; these proved to be non-microphonic and excellent sounding. The ECC99 required a heater rewire which, for the sake of completeness, I did and they seem to just edge it over the Russian valves in terms of tube sweetness and warmth. Like the others, these are also low noise and non-microphonic. TBH, I could easily live with any of these nine pin valves in a HPA input stage.

[Cressy Snr]

Anyway, here is how the HPA looks now. All JJ valves on the front row.
I’m listening more to the headphone system now than the main system, mainly because it's Wimbledon fortnight.

IMG_0481.jpeg (128.06 KiB) Viewed 72345 times

[Cressy Snr]

Whilst I was in the amp, I decided to reduce the dissipation of the power valves down to 10W, to improve their lifespans, by increasing the cathode resistor values. Of course the values around the input stage had to be altered too.

Schematic of the audio circuit:

HPACCT.png (57.57 KiB) Viewed 72343 times

[Cressy Snr]

The power supply:

HPAPSU2.png (88.92 KiB) Viewed 72342 times

[Mike H]

I'm surprised that works without some attenuation, to drop the level to the 'phones.

[Cressy Snr]

I'm surprised that works without some attenuation, to drop the level to the 'phones.

Hi Mike,
It works perfectly. The 'phones themselves are Hi-Fi Man Deva, 18R impedance planar magnetics, running off the 16R tap on the James OPTs.

Like most planar magnetics these are relatively inefficient for headphones at a mere 93dB, so they need plenty of drive. Trying to run them off a headphone jack on an iPhone is a joke. They 'work' off a phone output jack, but they clip the internal op-amp very easily. No such problem on this little beauty.

[Mike H]

Fairy nuff!

I consider myself told ...

[izzy wizzy]

I've always wondered why folk feed each channel with a wire and cap essentially putting those two caps in parallel. Are the two caps in parallel and that's the purpose or is there something else happening that I'm missing?

[Nick]

Topology can sometimes confuse.

[izzy wizzy]

Topology can sometimes confuse.

True. Hence the question.