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SCompRacer  
#1 Posted : Friday, March 11, 2016 7:10:31 AM(UTC)
SCompRacer

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This dual mono DAC/single Legato has been in operation for a little over four years. A couple months back, I removed the coupling caps (for the common mode DC issue) and disconnected the balanced ground. I run with just pos and neg balanced, no ground. I checked voltages and DC on the outputs and found .645v dc on the right balanced output. I could not null the right channel balanced DC. I thought I may have damaged the Legato right channel with static.

I installed another Legato and was able to null the right channel DC. I replaced all the transistors in the other Legato. I checked voltage today and find I have .584 v DC on the right channel balanced output, and I can't null it out. I install the rebuilt Legato, same thing, can't null the DC.

Is it possible the right channel DAC is the problem? Over the weekend I plan to assemble it as a single DAC with the left DAC board to see if I can null the DC in right channel.

Thanks,

Edited by user Saturday, March 12, 2016 8:29:27 PM(UTC)  | Reason: Not specified

gwikse  
#2 Posted : Friday, March 11, 2016 10:36:53 AM(UTC)
gwikse

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I have the same problem with an old B3 card that I have had lying around for some time and desided to use to test a legato 3.1 for headphone use. It worked a short while, then suddenly I had 0,5V DC on one channel output. Swapped the legato for another legato; same problem. Lifted the legato off the DAC card and the problem was gone. Put in an even older B2 card and hooked it up and still no issue going on 3 days. So in my case it is a damaged B3 card that was the cause for not being able to null out the DC on one of the channels.

I try to allways touch something that is connected to safety earth prior to working with cards, but now I am getting a proper antistatic bracelet d'oh!
thanks 1 user thanked gwikse for this useful post.
SCompRacer on 3/11/2016(UTC)
SCompRacer  
#3 Posted : Friday, March 11, 2016 2:18:02 PM(UTC)
SCompRacer

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I do have one of them ground straps and normally use it. When I removed the coupling caps, I was lazy and didn't.Shame on you

I've got a nasty head cold so thinking process is really slow....but if DAC board was bad how come I can null out DC on right SE output? Eh?
SCompRacer  
#4 Posted : Saturday, March 12, 2016 8:34:03 PM(UTC)
SCompRacer

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My two Legato's are fine, it is the right DAC. It was my slave DAC, I opened the address header ADDR 2 and removed R7 jumper, stuck it on the Legato. First thing I noticed was the Placid HD BP dropped in voltage from 15 to 4v on the negative side and had .569v DC on right balanced out. Put the left DAC back on, all is well.
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