Suggestions for balanced DAC output?

[ezkcdude]

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]

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

http://www.diyaudio.com/forums/showthread.php?s=&threadid=78968

 

[ecdesigns]

balanced outputs

Hi, ezkcdude,

I found this link:

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

It contains several balanced designs using single OP-amps

 

[ezkcdude]

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

 

[ezkcdude]

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]

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]

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]

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]

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

 

[ezkcdude]

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.

 

[wa2ise]

If you like tubes, here's a balanced in and balanced output DAC circuit using tubes. The 6111 is somewhat similar to a 12AU7. Low mu triode. The voltage sources represent the DAC outputs feeding the 150 ohm resistors as an IV converter. The rest of the tube circuit is a differential pair, with a pair of "SRPP" type output driver circuits.

 

[ezkcdude]

In the diagram I gave in my last post, the ratio of the resistor values gives the voltage gain. My question is how do you choose the actual resistor values? See the attached diagram. I've drawn the same circuit, but with different resistor values, each theoretically giving the same gain. What are the pros and cons of choosing lower valued vs. higher valued resistors in this op amp circuit? I have no idea.