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Old 17th April 2013, 04:49 PM   #81
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What purpose does the coupling caps fullfill? Any differential filter like this removes the DC offset within the limit of CMMR. I have none in my DIY analogue I/O to my DCX2496. DC on output is a few mV (OPA2134)
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Old 17th April 2013, 09:02 PM   #82
pilli is offline pilli  France
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Quote:
Originally Posted by rikkitikkitavi View Post
What purpose does the coupling caps fullfill? Any differential filter like this removes the DC offset within the limit of CMMR.
That's exactly my thought...
I am not qualified to really give an answer, but I'm "reading the books" looking for it.

In fact, the AKM Dac datasheets have examples of differential filters without coupling caps. Of course then you cannot use both phases for a differential output; (the so called differential output of the EMU 0404 is not really differential anyway... it's summed into a single ended signal and then this is copied into an inverted copy for he other phase. Like this they can use a normal stereo pot instead of four-way, I guess this is the reasoning...)

Do those coupling caps maybe make the filter "easier"?

Or is it because +/-6V supply to the opamps wouldn't leave enough headroom with inputs biased at 2,5V?

I will definitely try modifying the output filter to make it as in the datasheet. The EMU has two caps to ground, the datasheet just one across the two phases... easy to change.
Maybe it's not even necessary... I think I saw somewhere that somebody had shorted the coupling caps with no negative consequence.

I never got into filters...




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Old 18th April 2013, 09:16 AM   #83
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Just try to bypass the output caps with a piece of wire and check for DC offsets with a load connected on the output. If everything look acceptable check for possible THD disturbances. But it seems that should be safe to bypass the output caps.
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Old 19th April 2013, 10:54 PM   #84
pilli is offline pilli  France
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Quote:
Originally Posted by kannan_s View Post
Hi
did you check how the ADC quality of this unit ?
kannan,

Had you already seen this tread?

They describe a problem affecting the left channel input, and how to solve it.

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Old 19th April 2013, 10:59 PM   #85
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Yes I saw that - looks promising to invest on one used for my recording Audio cassettes!
thanks for your link
Kannan
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Old 26th April 2013, 07:30 PM   #86
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Hello everybody. I managed to modify the wiki adding all the stuff I've been able to gather while working on an EMU0404 of a friend of mine.
He asked me to modify it as some other guys did on the web. While I had it open, I identified some parts.
Hope you'll enjoy
Best,

Simone

p.s. I'm attaching the full post DAC schematic for having an URL for the wiki
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Old 29th April 2013, 07:42 PM   #87
sidiy is offline sidiy  Canada
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Hi Simone,
While on my unit the schematic is virtually identical to the one you posted some RefDes and values for the Left channel output are slightly different. Here are the differences I found comparing with mine; you may want to cross-check these:

R290, R268, R307 = 560R
R5 instead of R24, R5 = 22R
C15=68p
C121, C134 = 330p (soundwise the most important difference)
R154, R155 = 2.05k (nominal, just a technicality...)
Also AOL+ & C80 is swapped with AOL- & C81

best
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Old 29th April 2013, 08:10 PM   #88
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Quote:
Originally Posted by sidiy View Post
Hi Simone,
While on my unit the schematic is virtually identical to the one you posted some RefDes and values for the Left channel output are slightly different. Here are the differences I found comparing with mine; you may want to cross-check these:

R290, R268, R307 = 560R
R5 instead of R24, R5 = 22R
C15=68p
C121, C134 = 330p (soundwise the most important difference)
R154, R155 = 2.05k (nominal, just a technicality...)
Also AOL+ & C80 is swapped with AOL- & C81

best
Hello there.
Well I've just managed to modify the schematic which have been posted by pilli on the wiki. For what regards the output resistor, you're surely right, they're 560R. Creative itself says that in 0404 specs:
Quote:
Balanced/Unbalanced Output Impedance: 560 Ohms
R24: I've forgot to get the exact name for the left channel so I've just looked over the pics on the web for the name. That's because I don't have the 0404 I've worked on anymore (it's of a friend of mine).
C134: Are you sure about 330pF value? As I said, I can't check that anymore, but I measured 100pF. Will update for C121 anyway
R154,R155: well
C80,C81: maybe pilli just mistyped the two names
Thanks for looking, will update the wiki as soon as I can (I'm morated because I just lurked the forum 'til now. 2 posts and counting anyway )
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Old 29th April 2013, 08:14 PM   #89
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Just an update: didn't read I put value on C121 too.
I think I wrongly had taken note of the 2 values. Maybe C140/C110 too are not 3,3nF (could you check?)
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Old 29th April 2013, 08:16 PM   #90
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Forgot C15: that one was 82pF on mine for sure. Maybe your 0404 is the 1st model (blue top)?
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