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Old 26th January 2010, 09:41 PM   #1
jkeny is offline jkeny  Ireland
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Default DAC that will drive headphones directly

I'm using a ES9022 DAC chip to drive my Sony MDR-XD200 headphones directly (no caps, just 2V rms straight to headphones) but according to the ESS datasheet it shouldn't. The datasheet states min load of 5K and the h/p are 70 ohm load. Are my headphones high sensitivity & this is why it works or do I like the sound of distortion? So does anybody know a DAC that is designed to drive headphones directly?

I have tried a WM8051 Vout DAC which is designed to drive loads down to 16ohm @1Vrms but it has 2.5V riding on it's output so requires the DC to be blocked. I never like the sound of caps & they become expensive. Transformers will do it, sound wonderful but are bulky & expensive.

This topic was last aired back in 2005 there must be some advance in DAC output stages since?
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Old 26th January 2010, 10:59 PM   #2
jcx is offline jcx  United States
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I doubt many want to build high current op amps on DAC mixed signal CMOS process - a output amp built in a pure analog process will perform better and probably cost less per die area

certainly I wouldn't expect such integration in the high end - maybe someone wants a single chip mp3 player
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Old 26th January 2010, 11:08 PM   #3
jkeny is offline jkeny  Ireland
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Originally Posted by jcx View Post
I doubt many want to build high current op amps on DAC mixed signal CMOS process - a output amp built in a pure analog process will perform better and probably cost less per die area

certainly I wouldn't expect such integration in the high end - maybe someone wants a single chip mp3 player
I take your points. It was just that I came across the WM8501 DAC chip which although not stellar specs states that it is capable of driving a 16ohm load @ 1Vrms or 820 ohm @ 1.7V. I've listened to it through transformers to headphones & it sounds excellent. I wondered were there more out there?

I'm thinking along the lines of a HiFace with DAC - something portable but high quality - that headphones would plug into. The HiFace + ESS seems to be the snizzle at the moment so? I'll know better tomorrow at an audio meet-up with some AKG K701 & Seinnheiser HD650

Last edited by jkeny; 26th January 2010 at 11:10 PM.
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Old 26th January 2010, 11:57 PM   #4
wwenze is offline wwenze  Singapore
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I'd guess that in order to drive a headphone there'd need a built-in filter or driver/amp inside the DAC. But I'd rather get a DAC that doesn't and have an op-amp buffer, as an integrated driver would go against the idea of DAC driving headphones directly.

Why not an external buffer?

Add: btw most amps (unless bridged) powered by a single rail will have DC offset, so you can't escape the capacitor. I guess capless works for higher-end DACs with differential outputs... but stuffing a decent amp inside a DAC is already quite difficult (as you can see from their SNR), stuffing a pair for each channel, nah. Maybe I'd be wrong and such thing exist. Wish you good luck in yoru search.

Last edited by wwenze; 27th January 2010 at 12:17 AM. Reason: to be specific
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Old 27th January 2010, 12:24 AM   #5
jkeny is offline jkeny  Ireland
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Well, wwenze, here's the spec of the single 3.3V rail 24/192 ES9022 DAC which outputs 2Vrms using a charge pump to generate the neg rail & no DC on the output - DNR 112dB, THD+N -84dB@0dBFS. Not stellar, but OK & it sounds good in a size that is minute.

I'm really thinking of portability (something you can put in your pocket) with good sound rather than ultimate SQ

Last edited by jkeny; 27th January 2010 at 12:34 AM.
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Old 27th January 2010, 02:31 AM   #6
sangram is offline sangram  India
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Some of the PCM27xx chips can, but those are USB - meant for laptop speakers and suchlike. The 2702 is the best of the lot, and it can't, it needs a buffer...
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Old 27th January 2010, 07:32 AM   #7
wwenze is offline wwenze  Singapore
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Those specs probably don't apply for driving headphones though. But specs seldom say much on SQ anyway.

Found some WM DACs that can do "capless mode", but requires some care though:
http://www.wolfsonmicro.com/uploads/...en/WAN0131.pdf

If WM has quite a few it might be possible for others to have them too?

Last edited by wwenze; 27th January 2010 at 07:42 AM.
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Old 27th January 2010, 11:00 AM   #8
jkeny is offline jkeny  Ireland
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Originally Posted by wwenze View Post
Those specs probably don't apply for driving headphones though. But specs seldom say much on SQ anyway.
Agreed, they are for load >=10Kohm so I expect much worse than this performance but it does sound good - will hear it today on better cans & with some opinions from golden eared ones

Quote:
Found some WM DACs that can do "capless mode", but requires some care though:
http://www.wolfsonmicro.com/uploads/...en/WAN0131.pdf

If WM has quite a few it might be possible for others to have them too?
Thanks, wwenze, that was my thinking too - I'll have a look at WM some more. You set me thinking about a minimal class D solution - are TI Purepath chips the only ones that takes I2S input? Some of them have headphone outputs.
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