Not sure if this is the correct group to post this. If anyone can
suggest a more appropriate place, please do so.

I've just built a stereo balanced audio line driver using a pair of
Texas/Burr-Brown DRV134s. I've successfully built these with AD
SSM2142s in the past, but the AD devices are becoming hard to source
and the DRV134 is reputed to be better, so I used them this time.

The problem is that the V+ and V- outputs (on pins 1 and 8) are in
phase. This doesn't help when you're driving a differential input - the
result is silence, of course! I've wired the DRV134s up in accordance
with the data sheet, including the 10uF NP caps between signal and
sense pins. The only minor difference from typical application is that
the power supply is +/-12V rather than +/-15V.

Does anyone know of any condition under which the DRV134 outputs would
be in phase? Or have I simply misunderstood what this device is
supposed to do?

Clive Backham wrote:
> Not sure if this is the correct group to post this. If anyone can
> suggest a more appropriate place, please do so.
> 
> I've just built a stereo balanced audio line driver using a pair of
> Texas/Burr-Brown DRV134s. I've successfully built these with AD
> SSM2142s in the past, but the AD devices are becoming hard to source
> and the DRV134 is reputed to be better, so I used them this time.
> 
> The problem is that the V+ and V- outputs (on pins 1 and 8) are in
> phase. This doesn't help when you're driving a differential input - the
> result is silence, of course! I've wired the DRV134s up in accordance
> with the data sheet, including the 10uF NP caps between signal and
> sense pins. The only minor difference from typical application is that
> the power supply is +/-12V rather than +/-15V.
> 
> Does anyone know of any condition under which the DRV134 outputs would
> be in phase? Or have I simply misunderstood what this device is
> supposed to do?
> 
If you have wired up the DRV134 as shown in figure 2 of:
www.harvard.edu/~thunter/datasheets/drv135.pdf#search=%22DRV134%22" target=_blank rel="nofollow">http://cfa-www.harvard.edu/~thunter/datasheets/drv135.pdf#search=%22DRV134%22
I see no way the two outputs can be in phase.
Have you looked at the two outputs on a scope?

John Popelish wrote:
> If you have wired up the DRV134 as shown in figure 2 of:
> www.harvard.edu/~thunter/datasheets/drv135.pdf#search=%22DRV134%22" target=_blank rel="nofollow">http://cfa-www.harvard.edu/~thunter/datasheets/drv135.pdf#search=%22DRV134%22
> I see no way the two outputs can be in phase.
> Have you looked at the two outputs on a scope?

Thanks for your response.

Yes, I followed the B-B data sheet, and have checked the outputs on a
scope. They are definitely in phase. I've checked the PCB layout and am
fairly sure it's correct. But of course I could have made an error that
I haven't spotted. It's like proof reading your own words - it's easy
to miss a mistake.

So I guess what I'm asking is whether there is any way of wiring up the
DRV134 that delivers in-phase outputs. If I knew that, I could then
revisit the PCB to check whether that has happened.

Clive Backham wrote:
> John Popelish wrote:
> 
>>If you have wired up the DRV134 as shown in figure 2 of:
>>www.harvard.edu/~thunter/datasheets/drv135.pdf#search=%22DRV134%22" target=_blank rel="nofollow">http://cfa-www.harvard.edu/~thunter/datasheets/drv135.pdf#search=%22DRV134%22
>>I see no way the two outputs can be in phase.
>>Have you looked at the two outputs on a scope?
> 
> 
> Thanks for your response.
> 
> Yes, I followed the B-B data sheet, and have checked the outputs on a
> scope. They are definitely in phase. I've checked the PCB layout and am
> fairly sure it's correct. But of course I could have made an error that
> I haven't spotted. It's like proof reading your own words - it's easy
> to miss a mistake.
> 
> So I guess what I'm asking is whether there is any way of wiring up the
> DRV134 that delivers in-phase outputs. If I knew that, I could then
> revisit the PCB to check whether that has happened.
> 
If the chip is totally unpowered, the input signal leaks to both 
outputs through the various network resistors.  Is it possible there 
is a short circuit between the two outputs (measure with a meter)?

I can't quite figure out what would happen if you reversed the two 
sense feedback paths, but I don't think it produces your symptom. 
This chip is pretty simple.  An inverter and two subtractors that take 
the difference of the input and its inverse, with the subtraction 
reversed for one of the outputs.  I see no obvious way you could 
reverse the sense of one of the subtractions without altering the other.

Is the common signal on both outputs a good copy of the input, or it a 
very different magnitude?  Is there any load across the two outputs 
during your testing?

John, I've done some more testing and owe you an apology for wasting
your time. The signals ARE out of phase, as should be expected. I am
using a software 'scope, and was also using the PC as a signal
generator. It seems that the 'scope must have been picking up the
generated signal instead of the output of the line driver. Once I
dragged in a second PC to act as signal generator, I discovered that
the output is as it should be. Sorry once again, and thanks for taking
the time to try and help.

Clive Backham wrote:
> John, I've done some more testing and owe you an apology for wasting
> your time. The signals ARE out of phase, as should be expected. I am
> using a software 'scope, and was also using the PC as a signal
> generator. It seems that the 'scope must have been picking up the
> generated signal instead of the output of the line driver. Once I
> dragged in a second PC to act as signal generator, I discovered that
> the output is as it should be. Sorry once again, and thanks for taking
> the time to try and help.

Glad you solved your riddle.