[KevDo]

Just a quick question as to how I can test my balanced XLR outputs on my Cambridge DAC.
 
The problem is that one of the channels must be slightly louder (or the other quieter) resulting in an off-balanced centre.
 
I'm unsure if it's the input of my amp or the output of the DAC. I'm suspecting the DAC as I must have had a power surge at some point and one of the LED's in the DAC is intermittently dim/off/on.
 
I was going to use a tone generator on the PC through the DAC and use an oscilloscope to compare both the left and right outputs at different frequencies and volumes. The problem is, I'm not 100% sure on how balanced output work: if they're balanced in the DAC to the point both channels are balanced then or whether it's a "feedback" style system where the rely on feedback from the input device? If it's balanced in the DAC then  the comparison would work; if they need to be contacted to a balanced input then I'd have difficulty... unless there's a way of testing?
 
Thanks for any advice.

 

[samsquanch]

pump a 1k sine wave through the outputs of the DAC, the AC voltage difference between pins 1 and 2, 1 and 3, 2 and 3, should be the same for both channels.  All you would need is a DMM to test this.
 
If there's a severe imbalance, I'd check to see if the DAC is still under warranty and get it launched back at Cambridge.

 

[KevDo]

Thanks for the quick reply.
 
I do have good quality calibrated multimeters and digital and analogue scopes, function generators etc so any test method would suffice - whichever was more informative as to the problem.
 
I'll try you're method and see if there's much/any difference in outputs and see if that coincides with the "quieter" channel.
 
I just wasn't sure how balanced ouputs worked and if they were testable "open-ended" so-to-speak.
 
I'll give it a try. I really hope it is the DAC as I'm not fully happy with the sound; the amp is perfect for me though so I hope it's alright! (fingers crossed)
 
I think it is the amp though. I've tried the following, which would lead me to believe it is the amp. Testing the DAC would allow me to double check and rule out any possibility of phenomenon's or such like.
 
Swapped the cables over, used the left one for the right and vice-versa. (still quiet on left channel, cable ok?)
Swapped the cables over at the amp end only (still quiet on left channel, DAC output ok?)
 

 

[amb]

Quote:

Originally Posted by KevDo /img/forum/go_quote.gif
 
I've tried the following, which would lead me to believe it is the amp. Testing the DAC would allow me to double check and rule out any possibility of phenomenon's or such like.
 
Swapped the cables over, used the left one for the right and vice-versa. (still quiet on left channel, cable ok?)
Swapped the cables over at the amp end only (still quiet on left channel, DAC output ok?)
 

It's the amp.
 

 

[KevDo]

I tried listening again with the cables swapped at the amp end and it sounded like the right one was quieter.
 
Anyway... I ran a few different test tones through the DAC and observed the output of each set of pins on the left & right channels. Both channels were identical.
 
Checked the cables, again, no problem there.
 
Ran a signals through the inputs on the amp and was going to test the output but due to the Tripath digital amp I couldn't get a clean signal on the oscilloscope (even using low pass and notch filters) as the Tripath amp switches at above 550-600KHz (mine was 640KHz).
 
So I checked the input side, couple of SMD resistors and capacitors and an inversion buffer/amplifier. Everything seemed fine, input voltage and output voltages all identical. No noise to be concerned about.
 
I put the amp back together and while the case was still off the DAC I went over a lot of the solder joints just in case.
 
Put it all back together and it's fine again, just as the tests would indicate. The LED that was going dim/on/off now and then on the DAC is now perfectly solid.