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geekhack Community => Other Geeky Stuff => Topic started by: alaricljs on Fri, 11 May 2012, 20:48:48
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I don't frequent any audiophile forums, so I'm doing this here. Also some members have expressed interest as well.
I'm working on a headphone amp using Tangent (http://tangentsoft.net/audio/pimeta2/) and AMB (http://www.amb.org/audio/sigma25/) designs.
Some of the more interesting parts are the AD843JN op-amps, Alps blue velvet pot, and the nice black aluminum enclosure from Hammond.
Here's a pic of some of the parts on hand (others are still on the way):
[ATTACH=CONFIG]49956[/ATTACH]
I'll continue this with more pics and the build as time goes on.
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Had to post before bed.... I did take pictures along the way (mostly) and will be posting a lot more detail.
[ATTACH=CONFIG]51196[/ATTACH][ATTACH=CONFIG]51197[/ATTACH]
The brown and white rectangles on the underside are SMD caps... little bit of tissue that needs to be cleaned up too.
This is the board ready for power testing.
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place holder 2
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place holder 3
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place holder 4
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what was your decision process regarding the opamp? i'm want to more or less build the same amp using the blue velvet alps, wasn't sure which power adapter to go with either.
REALLY looking forward to your build. can you review the cost of the project too?
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before the rollback he said he was up to 250 with iirc almost all parts ordered
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So, honestly here was the process: read this page of Tangent's on Op-Amps (http://tangentsoft.net/audio/opamps.html) figure I've heard plenty of Burr-Brown and in fact haven't heard anything of quality that wasn't a BB. So why not try it? This will be the first time I'll have something that I can change it if I don't like it.
We are at ~$220 with mistakes.
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I read that page last night, along with the parts selection page and tweaks page. I've heard BB dacs, but never opamps so I don't have much to compare too. That said, being more than twice the price of the BB makes that opamp pretty attractive. Is your power supply going to integrated?
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Wall wart for AC, DC conversion/regulation inside the case.
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See post 2 for some pics of the Pimeta ready for power testing.
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This project would feel perfectly at home here (http://www.diyaudio.com/forums/headphone-systems/), too.
An AD843 seems like a bit of an odd choice for a headphone amp. Sure it's fast and all, but rather on the noisy side of things at 19 nV/sqrt(Hz), not to mention spendy. (Both the AD8610/20 and the popular OPA(2)132/134 show much less voltage noise.) While the PimetaV2 is not exactly a low-noise design to begin with (resistors alone contribute about 12 nV/sqrt(Hz), minimum), this opamp's input noise would easily dominate here. At standard gain, expected output noise level is 18 µV within a 20 kHz b/w, or -95 dBV. Expect perceptible background noise with (mostly) IEMs in the 120+ dB/V category. Plus, you'll need adapters for two single opamps where one dual goes, which add parasitics and hopefully ship with decoupling caps.
I'm not sure why R1 = 4k32 was chosen. This places the point of minimum input impedance distortion at absolute minimum volume, which makes little sense and requires an exotic resistor value. 3k9 would have been just fine. (It makes more sense for the ground channel where impedances are, in fact, balanced, though obviously one could equally swap the 4k32s with 3k9s there.) I'd also prefer a lower-impedance pot than the standard 50k, which may add up to 12k5 of source impedance... something like 20k or 10k, like the O2 (http://nwavguy.blogspot.de/2011/08/o2-summary.html) does.
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1) i have no idea what your post says, lol. do you have a layman's translation of that?
2) why haven't you volunteered to help out with our pcb design efforts yet? ;)