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I am trouble shooting a B-III/IVY-III set up for a friend. After some work I have got it all working, but here is still a small problem: one channel of the IVY-III has significant DC offset (~82 mV SE, same on balanced), the other channel is fine, and the offset from the B-III is equal for both R and L channels.
The soldering quality on many joints is questionable, any particular joints to go over which might cause the problem? Or, is it more likley that one of the OPA 1632s is damaged causing the offset?
Thanks for any help.
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Additional detail: the excess offset is caused by the B-III. Without the B-III in place offset is near 0 mV. But, the offset measurement on the output pins of the B-III is the same in both channels (~1.3 V). It is puzzling how this B-III is producing ~90 mV offset at the output of the IVY III?
I tried this B-III with my own IVY III with identical results, it resulted in ~90 mV offset in one channel, equally distributed acorss both phases. Otherwise, everything is working fine. Anyone have any ideas?
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It is not causing it, it is simply driving some current through what appears to be a slight impedance imbalance. This could be an issue of resistor matching.
Are all the parts stock?
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Rank: Member
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Russ: the parts on the IVY-III are stock. What is odd though, is that I put this B-III on my (different) IVY-III for testing, and had the same result: ~88 mV DC, evenly distributed on the two phases, very, very strange, as my IVY-III had just a couple of mV DC with my B-II on it. Resistors on my IVY-III are non stock (PRPs) but matched to .1% or better, the (other) unit I am testing is built with the stock, supplied resistors in the kit. Bottom line, this B-III produces an identical problem on two IVY-IIIs, and my B-II does not produce the problem, very, very odd... Edited by user Wednesday, August 1, 2012 4:32:03 AM(UTC)
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Rank: Member
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I found the problem: Russ' mention of a current imbalance got me to thinking... and sure enough, the builder had damged the B-III board, so that even though the output jumpers were in place, one of the outputs was not joined (the through hole plate had been ripped out). I went ahead and exposed the trace for that output, jumped it in with small strand of wire, and, voile, excess DC at IVY-III output gone.
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