Custom OTL Headphone Amplifier / DAC

[Jerm111]

Hi everyone,

I've been a member of Head-fi for a while and have visited sporadically over the years. After finishing my first DIY amp build I thought i'd come and share it with you guys. I'm a novice when it comes to electronics, especially tube amps, so I am fortunate to have the help of my Dad who is fairly experienced in DIY audio gear.

The amplifier is based off a well-known OTL amp circuit which utilises 12AU7/ECC82 input & 6080 triodes and is output transformerless (OTL). It should pair nicely with the high input impedance of my my Sennheiser HD6xx headphones. Input options are either switchable line level analogue or USB digital. Digital input is provided via Khadas Tone Board. It currently has GEC CV 2984(6080) and GE 12AU7 tubes installed. These were what we had in stock / available at the moment and I had planned to upgrade them. After some research it seems the CV 2984 is quite well regarded and an upgrade would be quite costly, but i'm interested in any recommendations.

This amp will predominantly reside on my desk at work, the decision was made to integrate a high quality DAC as I have found the sound output of modern office PCs to be quite poor.

My existing setup (which served me well) was a JDS Labs O2 + ODAC. I’m not one to do exhaustive reviews and AB comparisons of my gear, but I will say that so far this new setup is a step-up in sound quality. More detail, smooth bass, increased dynamics and sound stage. Currently I am using a GEC CV2984/6080, I would like to try a few different tubes and see what effect that has, perhaps brighten the top-end a little.

I’m very happy with how it turned out. I've attached some pics below but there are more pics and full build documentation on my blog if anyone is interested. https://jeremyyoungdesign.com/2020/04/13/otl-headphone-amplifier-dac/

Cheers,
Jeremy

 

[ScornDefeat]

Hi everyone,

I've been a member of Head-fi for a while and have visited sporadically over the years. After finishing my first DIY amp build I thought i'd come and share it with you guys. I'm a novice when it comes to electronics, especially tube amps, so I am fortunate to have the help of my Dad who is fairly experienced in DIY audio gear.

The amplifier is based off a well-known OTL amp circuit which utilises 12AU7/ECC82 input & 6080 triodes and is output transformerless (OTL). It should pair nicely with the high input impedance of my my Sennheiser HD6xx headphones. Input options are either switchable line level analogue or USB digital. Digital input is provided via Khadas Tone Board. It currently has GEC CV 2984(6080) and GE 12AU7 tubes installed. These were what we had in stock / available at the moment and I had planned to upgrade them. After some research it seems the CV 2984 is quite well regarded and an upgrade would be quite costly, but i'm interested in any recommendations.

This amp will predominantly reside on my desk at work, the decision was made to integrate a high quality DAC as I have found the sound output of modern office PCs to be quite poor.

My existing setup (which served me well) was a JDS Labs O2 + ODAC. I’m not one to do exhaustive reviews and AB comparisons of my gear, but I will say that so far this new setup is a step-up in sound quality. More detail, smooth bass, increased dynamics and sound stage. Currently I am using a GEC CV2984/6080, I would like to try a few different tubes and see what effect that has, perhaps brighten the top-end a little.

I’m very happy with how it turned out. I've attached some pics below but there are more pics and full build documentation on my blog if anyone is interested. https://jeremyyoungdesign.com/2020/04/13/otl-headphone-amplifier-dac/

Cheers,
Jeremy

This is beautiful work! Love the look of it and really impressed with the integration of a Khadas Tone Board!

 

[Jerm111]

This is beautiful work! Love the look of it and really impressed with the integration of a Khadas Tone Board!

Thanks! Yes as the amp was to reside mostly on my desk at work plugged into my Dell PC the integrated DAC was a no brainer. Interestingly, during initial tests before I mounted it inside the case I was running it via a fairly long RCA cable into the input on the back of my amp, it sounded ok. When I mounted it inside and hard wired I noticed a significant increase in sound quality, I guess that reinforces the idea of having a nice short signal path is good for the sound!

 

[ScornDefeat]

Thanks! Yes as the amp was to reside mostly on my desk at work plugged into my Dell PC the integrated DAC was a no brainer. Interestingly, during initial tests before I mounted it inside the case I was running it via a fairly long RCA cable into the input on the back of my amp, it sounded ok. When I mounted it inside and hard wired I noticed a significant increase in sound quality, I guess that reinforces the idea of having a nice short signal path is good for the sound!

For your use case, you can't beat the convenience of integrating the DAC. Khadas Tone Board measures very well and seems like a good, transparent choice here. I feel something like the Starting Point Systems DAC2 could be integrated/mounted, as well, for a NOS DAC option.

Your amp not only sounds like it performs very well, but is a work of art. I'm jealous of how beautiful, right down to that transformer cover!

 

[carlman14]

Great job! The Khadas board was a great idea. I might have to try this in one of my amps. If you don't mind me asking, what are those RCA hardwire cap things you have on the Khadas RCA jacks? Also, what selector switch did you use?

 

[Jerm111]

Great job! The Khadas board was a great idea. I might have to try this in one of my amps. If you don't mind me asking, what are those RCA hardwire cap things you have on the Khadas RCA jacks? Also, what selector switch did you use?

Thanks. They are just really minimal rca plugs, my Dad had them in stock so I used them. They are basically just a metal shell with a pin in the middle that you solder on to. I've had a look but I can't seem to find them for sale, i'll see if I can find out.

for the switch I just used a basic toggle switch, from the local electronic store, link below.
https://www.jaycar.co.nz/dpdt-miniature-toggle-switch-solder-tag/p/ST0355

 

[carlman14]

Thanks for the info. I actually found those RCA plugs this morning: https://www.digikey.com/product-detail/en/keystone-electronics/561/36-561-ND/2466

 

[Jerm111]

Thanks for the info. I actually found those RCA plugs this morning: https://www.digikey.com/product-detail/en/keystone-electronics/561/36-561-ND/2466

Cool that's good to know, I might be keen to get some more. There's a theory that minimising metal mass has sonic benefits and these are about the most minimal RCA plugs I've seen.

 

[gimmeheadroom]

I've got a work buddy who just moved to Auckland. He's not on this forum and he's rather a fan of iAnything. I'll point him here just in case

 

[monkey5949]

Damn brother.....stupendous work!

 

[gimmeheadroom]

Damn brother.....stupendous work!

No kidding. It's hard to declare whether the cabinetry or p2p wiring are more beautiful.

 

[Jerm111]

Damn brother.....stupendous work!

Thanks!

Hey, this is off topic but I noticed in your sig you list some campfire IEMs and also the TIN series.

I've been reading and watching online and it has made me really curious about what a real high end set of IEMs like the Campfires are like. My budget would barely stretch to the IOs, are they worth the extra money when compared to the many other offerings at $100-200?

I'm not that experienced with IEMs and just got a pair of KZ ZS10 Pro, I only received them today but so far I think they sound pretty good, maybe a bit sharp in the treble, will see how they go over the next few weeks.

I'm also thinking about trying one of the Tin models, maybe the T4.

Do you have any recomendations?