Suggestions for balanced DAC output?

ezkcdude · 16th May 2006, 01:57 PM

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.

hifimaker · 16th May 2006, 03:35 PM

There's a discussion about this topic in the Pass forum:

Anyone built a Pass D1 I/V for a TI1794 or TI1794 DAC?

-ecdesigns- · 16th May 2006, 04:24 PM

Hi, ezkcdude,

I found this link:

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

It contains several balanced designs using single OP-amps

ezkcdude · 16th May 2006, 04:28 PM

Thanks, I guess I have a lot of reading to do!

ezkcdude · 16th May 2006, 04:37 PM

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.

jleaman · 16th May 2006, 04:44 PM

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 ?

ezkcdude · 16th May 2006, 05:12 PM

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.

ezkcdude · 17th May 2006, 03:39 AM

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.

00940 · 17th May 2006, 07:51 AM

it's just a passive I/V conversion followed by a balanced to single ended converter.

ezkcdude · 17th May 2006, 11:27 AM

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.

16th May 2006, 01:57 PM	#1
ezkcdude diyAudio Member Join Date: Dec 2005 Location: Atlanta	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.

16th May 2006, 04:24 PM	#3
-ecdesigns- diyAudio Member Join Date: May 2006	balanced outputs Hi, ezkcdude, I found this link: http://sound.westhost.com/balance.htm It contains several balanced designs using single OP-amps

17th May 2006, 07:51 AM	#9
00940 diyAudio Member Join Date: Sep 2003 Location: Paris	it's just a passive I/V conversion followed by a balanced to single ended converter. __________________ Ben.

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16th May 2006, 03:35 PM	#2
hifimaker diyAudio Member Join Date: Oct 2003 Location: San Jose	There's a discussion about this topic in the Pass forum: Anyone built a Pass D1 I/V for a TI1794 or TI1794 DAC?

16th May 2006, 04:28 PM	#4
ezkcdude diyAudio Member Join Date: Dec 2005 Location: Atlanta	Thanks, I guess I have a lot of reading to do!

16th May 2006, 04:37 PM	#5
ezkcdude diyAudio Member Join Date: Dec 2005 Location: Atlanta	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.

16th May 2006, 04:44 PM	#6
jleaman Banned Join Date: Apr 2002	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 ?

16th May 2006, 05:12 PM	#7
ezkcdude diyAudio Member Join Date: Dec 2005 Location: Atlanta	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.

17th May 2006, 11:27 AM	#10
ezkcdude diyAudio Member Join Date: Dec 2005 Location: Atlanta	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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