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Discussion Starter · #1 ·
I decided to add a Velodyne CHT-12 in my theater to support my old BA SW-10.


I put a y-cable on the sub output on my Onkyo 702 receiver to split the signal. I have a regular RCA cable going to the BA about 6' away and a DIY RG6 cable going to the CHT about 25' away. Both have a y-cable going into the inputs. The BA also has a ground wire that is connected to the receiver. Both are plugged into the same dedicated 15 amp circuit, no protector/conditioner. Receiver is on dedicated 20 amp circuit.


I'm getting a hum from both when I have everything hooked up, more pronounced in the CHT. When I pull the interconnect on either the hum goes away.


Any ideas on how to get rid of this?
 

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You probably need a buffer to lower the load on your receivers sub output.
 

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Quote:
The BA also has a ground wire that is connected to the receiver.
What is this ground wire for? That sounds suspect. Is it required? Does the hum go away if you remove the ground? You could also try connecting the receiver and both subs to the same electrical circuit. What if you reverse the subs and put the velo on the shorter cable?
 

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Discussion Starter · #4 ·
Dan,


How would I "buffer" the signal? I haven't heard of that before.


Billybob,


I haven't tried removing the ground. I've always had it hooked up since I got another type of hum when it was disconnected and the BA was the only sub. I'll try removing it. I'll also try reversing the wiring.


I can't put the receiver and subs on the same circuit. The receiver is in a separate equipment room.


Thanks for the ideas so far!
 

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You have a bad Y-cable.


Or are the subs plugged into two different outlets?
 

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At this point, you should just be trying to isolate the problem - you could try using an extension cord temporarily to test what happens if they are all on the same circuit. The fact that you had previously had a problem with just the one sub that was solved by running a ground between it and the receiver is indicative of a grounding problem in your house's wiring. It sounds like the two circuits are not using a common ground.
 

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A buffer is an amp with a gain of 1. It's not a power amp, but a small op amp like OPA134, OPA627, etc. Since this involves adding equipment, test out the other possibilities first. But the buffer would be really cheap to make if it comes down to that.


Here's an idea: try taking an ohmmeter (has to be an accurate and precise meter) between the input ground of each sub. It should be as close to 0 as possible.
 

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Discussion Starter · #9 ·
OK, I've tried several things, but no luck.


*I plugged the two subs into the same outlet, making sure there was absolutely nothing else plugged into that circuit.

*I plugged them into the same circuit as the receiver.

*I ran one RCA cable from the receiver and did a splitter off the end for the subs.

*At each of these combinations I also connected and disconnected the ground wire from the BA.


My ohmmeter is broken so it looks like I need to get a new one. I'd also appreciate a link to some more info on a buffer.


I'm also going to try swapping in a third subwoofer and see if that makes any difference.


Thanks for the help so far. Keep any ideas coming.
 

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You're going to think this is crazy but it worked with a JBL sub I once had. If your sub has speaker level ins/outs connect a piece of speaker wire to the speaker level in or out (try both one will probably make it worse and one better). Then touch the other end to the grounding screw of the outlet(you know the center screw that holds on the plastic cover plate of the outlet your sub is plugged into).


When I did this the hum was gone.
 

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Discussion Starter · #15 ·
Well, I took the BA SW-10 out and put in a Dayton 10". Hum is gone.


Now I have to figure out what's going on with the BA. Works fine by itself, but doesn't like to be paired up.
 

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When you took out the BA, did you also remove the extra ground wire that went back to the receiver? I still think that ground wire is indicative of something funky - probably stating the obvious - it sounds like the amp in the BA has some sort of ground problem.
 

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Discussion Starter · #17 ·
The ground was a part of the original setup of the sub. Part of the design. Yes, I tried with the ground connected and unconnected. I agree, there is probabably something amiss with the sub's amp, but I'm pretty sure it has nothing to do with the extra ground wire. Unless the ground wire is producing some incompatibility with the Onkyo receiver.
 
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