Page 2 of 2

#16 Re: New Headphone Amp

Posted: Mon Jun 15, 2020 11:17 am
by izzy wizzy
Here's the 2 to 1 b9a adaptor gizmo. It works surprisingly well. Going to make another for other channel after more listening yesterday.


#17 Re: New Headphone Amp

Posted: Mon Jun 15, 2020 11:39 am
by Cressy Snr
Cool 😎

#18 Re: New Headphone Amp

Posted: Mon Jun 15, 2020 9:30 pm
by izzy wizzy
Gone for stereo with 2 adaptors so now line/headphone is 12B4-A. Very pleased so far. There's been some glare that's been bugging me for some time and as I've fiddled with everything else, it hasn't entirely gone away until now ... hopefully.

I'm not saying that it's a characteristic of the 6N6 but in this circumstance, compared to the 12B4, they were a bit shut in, dirty sounding with a bit of glare that was like squinting with your ears. I'm not sure of that's why Steve doesn't like "Russian valves" or why in another thread there was a bit of a downer on the 6N1P as well as the 6N6 (something to do with an Aikido?)

Anyhoo, the gain is well down on the 6N6, about 8dB less but luckily I have that to spare with a bit more to play with yet. Off to play some more tunes :D

#19 Re: New Headphone Amp

Posted: Mon Jun 15, 2020 9:42 pm
by IslandPink
Is that 6N6 or 6N6P ?
I like the 6N6P a lot, but you have to avoid the gold-grid ones.

#20 Re: New Headphone Amp

Posted: Mon Jun 15, 2020 10:03 pm
by izzy wizzy
I seem to have 6N6P and no gold. I'm not saying it's bad sounding but for what I'm doing the 12B4 is a bit of a revelation :bounce:

#21 Re: New Headphone Amp

Posted: Tue Jun 16, 2020 9:42 am
by Nick
I seem to remember that years ago when playing with 6n6's (for a balanced output stage in a dac so very similar to what you are doing) I found that there were good ones and bad ones from the same batch. Some were very clean others had lots more distortion. And like I found when looking at some Russian pentodes there were two sorts, with distinct performance. That is to say they were either good or bad, there was none I found that were between the two sets of results.

For the dac I ended up using 5687 as they were just consistent.

#22 Re: New Headphone Amp

Posted: Wed Jun 17, 2020 9:58 am
by izzy wizzy
I was going to use the 5687 but I already use one in the phono and don't like to repeat things in the chain. Hence the 6N6P. Maybe a silly prejudice. But also interesting you say that Nick.

This 12B4 thing is a bit of a game changer for me. I could rant on and on but will try not to which is why I've held off for 3 days saying anything too much about it. I suspect we have an idea as to what we're after in our heads. Hence Mark's Undergrowth thread maybe. I've had a few firsts these last few months. First the Hana gets through a record and I really don't know where it is on that record. It just does the job and beautifully. Now putting the 12B4 in made sounds I have had in my head that I want to hear, particularly on brass for one. And the thing that's been bugging me for a while, about something in the way but not quite sure what it is has been reduced substantially; a huge amount. Hence the Resistors thread which was me trying to address the issue and it helped and now I think this reveals just how good that detour was.

Again, not saying the 6N6P is no good it's just that the 12B4, for this application, is in another league. I also run quite long interconnects and there's more benfit for the amplifiers than on headphones if that makes sense.

But .... there's no gain in the amp now so it's very close to not having enough. I suppose there's a comfort in having the volume at about 2pm but when there's only 3 clicks left, 6dB before max (it's pretty loud by then) .... hopefully it will be fine. Time to build it properly.

#23 Re: New Headphone Amp

Posted: Sat Jun 20, 2020 12:16 pm
by izzy wizzy
Rebuilt the audio bit. There's not a lot of room on my breadboard in a box thing. Just for giggles, here's some pics.


I know I'm not breaking any new ground with all this. Found a thread dating back 15 years on Intact Audio with Mark from here and I think James too discussing all this kind of shenanigans.

Listening these past few days may indicate that the vinyl is more improved than the digital. Possibly as it's the better source. Maybe as there's 4to5 times the grid bias so way more overload capability /headroom which is important when the attenuator is on the output. In the past, headroom for vinyl is usually a major winner for lower noise and less distortion.

Anyhoo, before I could even consider DHTs in here, I'd need another case situation. Something for the future.

#24 Re: New Headphone Amp

Posted: Thu May 27, 2021 10:28 pm
by ruffrecords
HD650 phones are interesting, not just for their sonic qualities, but also because their impedance is 300 ohms which makes them much easier to drive with valves. I could not find a sensitivity figure in their data sheet. All they quote is an output level of 103dB (SPL) but without specifying the conditions. is this likely to be with 1V rms applied?



#25 Re: New Headphone Amp

Posted: Fri May 28, 2021 9:33 am
by izzy wizzy
I've not done any measurements. All I know is that they go plenty loud for me with attenuation through the 12B4 line which has no gain flat out off the output of the RPi using iqaudio dac.

I've decided to not go the dht route here and am in the process of adding the dht stage to the power amps.