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Xlr to rca

Hello, I am trying to hook up a large bgm model 620 b pro amp to my stereo, it only has 1/4" jacks, it was given to me with an 1/4" to rca 1.5m cable, I've tried hooking this up to a luxman stereo reciever and to a McCormack tlc-1 pre amp both of which have two sets of pre outs, I cannot have the outs connected to my velodyne hts15 sub and to the bfn amp at same time without mad hum, if I disconnect the sub or the bmg rca either one all the hum goes away the hum is present in both the main speakers on bgm and in the sub, the cable is wired from center pole of 1/4" to center pole of rca I was wondering if there is a pole difference between old pro audio and home audio, should I flip it so it center pole to outer and vise versa? I've tried various grounding options with no luck, but it sounds like a ground loop. Any thoughts on how to fix?
ryedady
danoroo
239 posts
 
@ryedady

Are you trying to run cables from the rca outputs of your Luxman/McCormack to the 1/4" inputs of the bgm?  If so, there is probably an impedance or signal level mismatch.  1/4" sockets are usually intended for microphone or electric instrument connections. Such sockets are fairly sensitive because the intended instruments emit a weak signal (about 50 millivolts).  Line level RCA outputs from stereo pre amps usually output a considerably higher voltage.  With the subwoofer disconnected, have you tried to play any source material through the bmg amp?
ryedady OP
15 posts
 
Actually the input gain on bgm amp is much lower then standard, everything works fine until I plug in something else to the other set of pre outs, it did the same thing on my luxman. Its either a ground loop or a polarity thing. I will just have to bite the bullet and re terminate some cables to eliminate if that doesn't work I have no idea how to eliminate a ground loop from the rca jacks, maybe solder onto the negative pole of one set and run it to the earth ground of electrical socket
ryedady OP
15 posts
 
https://www.parts-express.com/hosa-cpr-202-dual-1-4-ts-to-dual-rca-stereo-interconnect-2m--241-9011
ryedady OP
15 posts
 
Its basically those cables but Idk if the wiring is same on mine
ryedady OP
15 posts
 
https://www.bhphotovideo.com/c/product/828249-REG/Hosa_Technology_HPR_020X2_HPR_0020X2_Dual_1_4_TS.h...

Actually that's it there, I'm guessing its a ground loop, 
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