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Old 18th May 2008, 08:36 PM   #1
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Default dddac output cap question

Hi all

I have a dddac USB 1543 board schematic here:

http://www.dddac.de/files/dddac-usb-1543-dac32.pdf

It's feeding a unity gain buffer that has dc blocking caps on the output so would it be ok to ditch the output caps on the dac and just short them? I imagine this would give a noticeable improvement in sound quality.

Many thanks
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Old 18th May 2008, 08:46 PM   #2
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Do you have any significant DC now? You haven't asked the designer?
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Old 18th May 2008, 09:09 PM   #3
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I thought it would be a simple question so decided not to bother him with it. Also thought I may get a swifter reply here.

I suppose what I'm really checking is that the output caps don't serve any purpose other than DC blocking. I'm pretty sure they don't but just wanted to check before removing them. I can't see any reason the buffer would mind a little DC (its the discrete transistor buffer from dec dun) and the cap on the buffer output will stop the stray DC from getting into the power amps/speakers
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Old 18th May 2008, 09:54 PM   #4
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Should be fine as long as your buffer doesn't include a volume control.
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Old 19th May 2008, 08:03 AM   #5
ssmith is offline ssmith  France
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out of curiousity, what buffer are you using, and what made you decide you needed a buffer?
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Old 19th May 2008, 09:43 AM   #6
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Dont know the answer with the buffer, It will depend on how much DC voltage it is capable of handling. I believe, that the DDAC has a fair bit of DC coming from it. I cant remember how much, but the manual may mention it for testing info.

Are you using the cap combination that comes as standard with the DDAC at the moment? The combo that Doede suppies should only be considered for testing purposes.

I replaced it with Sonicaps, bypassed with MKP1839's. Because the caps required are of a very low value, it was a pretty cheap upgrade. The sound from these caps is pretty damn good.

Why not just check the dc output with a mulitmeter? There are three pins on the ddac for output is I remember correctly, Lout, Rout and GND. Measure here.
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Old 19th May 2008, 10:15 AM   #7
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The DDDAC has a few volts on it's output (I built one a while back, but can't remember the figure). The only issue with the buffer is whether it will clip, but with a voltage supply greater than that of the DDDAC itself (e.g. at least +/- 9V) you'll be fine.

Dan
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Old 19th May 2008, 10:46 AM   #8
ssmith is offline ssmith  France
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Quote:
Originally posted by justblair
The combo that Doede suppies should only be considered for testing purposes.

I replaced it with Sonicaps, bypassed with MKP1839's. Because the caps required are of a very low value, it was a pretty cheap upgrade. The sound from these caps is pretty damn good.
I tried:

Audyn cap plus (0.47uf)-- nothing to write home about
Obbligatto (1uf) -- much nicer
BG 'N' (4.7uf) electrolytic -- tonal balance and clarity that seem just right in my set-up.
BG NH (150uf) electrolytic -- ditto.

IIRC Peter Daniel likes BG N's on the output of his NOS DAC.

think the trick here is to experiment and find the best match for your ears/system.

I have a pair of Sonicap 22uf caps for tweater protection (biamping) and they are very nice. Haven;t tried them on the dddac output though.
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Old 19th May 2008, 12:28 PM   #9
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Quote:
Originally posted by ssmith
out of curiousity, what buffer are you using, and what made you decide you needed a buffer?

Click the image to open in full size.

That's the buffer I'm using. It's on +/-15V so clipping will certainly not be an issue. I can't see why it would have a problem with a few DC volts but I'm no electronics expert and thats why I'm asking.

I have currently replaced the caps with Panasonic FCs that I had, but I think shorting them and letting the buffer's output cap block the DC would sound better than any output caps on the dac

Thanks for all the replies
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Old 19th May 2008, 09:44 PM   #10
dddac is offline dddac  Germany
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i see no issue as well. the current source below the npn will absorb this dc bias voltage

i also see no need for the 68 ohm in series ?

regards
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