kwingylee Posted February 15, 2012 Share Posted February 15, 2012 All: I have been running my system in full balance mode using the EV DX38 as active XO. I have not done the so call Roy mod. Is that for XLR>RCA In the last week, my power amp developed large hum noise when the XLR input cables are plugged in. The hum noise is there even if the other end of the XLR cable is open. I went on to use the RCA inputs from the amp and everything is fine. I tried 3 diff sets of balance cables and they all hum. Lifting the ground from the AC plug did not help. Do the home audio XLRs follow the same scheme as the PRO world? I note that there is a small capacitor from pin 1 to ground. Is this common practice in the pro world? Do they leave pins 1grounded and shield floating? Looking for answers... appreciate the help in advance. Quote Link to comment Share on other sites More sharing options...
kwingylee Posted February 15, 2012 Author Share Posted February 15, 2012 Appreciate if someone can point me to the DX38 mod.... Quote Link to comment Share on other sites More sharing options...
RRFL Posted February 16, 2012 Share Posted February 16, 2012 Before you alter things consider that the problem was not there about a week ago. It is therefore necessary to find out what changed before all else. You must recreate everything from just before the hum started like a detective. As far as I am aware xlr to xlr connections are standard. The shield is pin1 ground relative to the pair of differentially balanced conductors as pin2 hot and pin3 cold. Ensure you check the actual numbers on each connector as just looking at the back of both ends of a cable together can be confusing and pins 1 & 2 are sometimes swapped by accident. A DMX lighting control cable can also have xlr connectors and it's wiring is different. Check every connection for good contact as corrosion due to current flow through connections is possible. To clear this plug in and out connections several times. Quote Link to comment Share on other sites More sharing options...
kwingylee Posted February 16, 2012 Author Share Posted February 16, 2012 Thanks Rod, With the help of teh amplifier rep, I was able to locate the problem to a switch in the back of the amplifier that flows the ground wire from the basis. I also found a few noisy tubes from the preamp and replaced them. Everything is soaking now and all is quiet again. Quote Link to comment Share on other sites More sharing options...
Moderators dtel Posted February 16, 2012 Moderators Share Posted February 16, 2012 Glad to hear that, good luck. [Y] Quote Link to comment Share on other sites More sharing options...
RRFL Posted February 17, 2012 Share Posted February 17, 2012 [] Quote Link to comment Share on other sites More sharing options...
Chris A Posted February 17, 2012 Share Posted February 17, 2012 Appreciate if someone can point me to the DX38 mod.... http://community.klipsch.com/forums/t/124341.aspxhttp://community.klipsch.com/forums/storage/3/768134/XLR-Unbalanced-EV-Dx38.jpg Quote Link to comment Share on other sites More sharing options...
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