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Old 16th May 2006, 01:57 PM   #1
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Default Suggestions for balanced DAC output?

So, I'm desiging a DAC which will use PCM1794, and I want to have balanced output. I'm trying decide between using fully differential op amps (e.g. OPA1632 or AD8138) or separate op amps for + and - signals (possibly AD8065/6 or AD8610/20). Does anyone have specific suggestions/advice/experience doing this? It seems there are not too many balanced designs out there.
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Old 16th May 2006, 03:35 PM   #2
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There's a discussion about this topic in the Pass forum:

Anyone built a Pass D1 I/V for a TI1794 or TI1794 DAC?
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Old 16th May 2006, 04:24 PM   #3
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Default balanced outputs

Hi, ezkcdude,

I found this link:

http://sound.westhost.com/balance.htm

It contains several balanced designs using single OP-amps
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Old 16th May 2006, 04:28 PM   #4
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Thanks, I guess I have a lot of reading to do!
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Old 16th May 2006, 04:37 PM   #5
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ece, just read that link. I think maybe the balanced line receiver approach might be the best for me. It's a single-ended output, but probably has most of the benefits of a balanced design anyway (i.e. common mode rejection). Since I won't be driving very long cables, maybe it's not essential to have true balanced outputs. Also, it appears like a very simple design, and is already suggested in several data sheets that I've been looking at.
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Old 16th May 2006, 04:44 PM   #6
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I wonder if some one has a really good ciruit to turn a non balanced dac into a good performing dac with balanced. I guess i could use DRV134's but are they really that good ?
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Old 16th May 2006, 05:12 PM   #7
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I would imagine one way of doing this is to split the single-ended signal into two op amps, one inverting and the other non-inverting. I suspect that maintaining correct phase of the signal may be pretty hard.
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Old 17th May 2006, 03:39 AM   #8
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There's a very simple circuit diagram for balanced to single-ended conversion in AD's "Data Conversion Handbook" (Fig. 6.70 on p. 417). I think I may just try this design first, at least, in the prototyping stage. I've attached a schematic of the I/V stage with the PCM1794, if anyone's interested. I should note that I've drawn it using AD8620, which is a dual op amp. This is a convenient choice because you can get a Brown Dog pre-mounted DIP.
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File Type: pdf pcm1794sch.pdf (21.0 KB, 314 views)
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Old 17th May 2006, 07:51 AM   #9
00940 is offline 00940  Belgium
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it's just a passive I/V conversion followed by a balanced to single ended converter.
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Old 17th May 2006, 11:27 AM   #10
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Yep. I've changed my mind about keeping the output balanced. This method still has the advantage of common mode rejection, which I think is important. It's also about as simple as an op amp setup can be. Also, the AD862X has specs very similar, if not better, than OPA627.
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