Rel Hum issue with PS Audio Stack

Trying to solve a weird hum issue. THIS ISSUE OCCURS WHEN THE AMP IS POWERED ON.

My system includes:
BHK Pre Amp
BHK 250 Amp
P15 Regen
2x Rel T9i

I’m connecting just the red spekon wire for each sub to the corresponding speaker terminal. Black wire from each spekon cable is floating. I’ve watched all the Rel vids and have tried connecting the black to chassis ground as well as keeping it unconnected and running an rca cable from the pre amp to the life on each sub. None of this has helped. The weirdest thing is only one of the subs hum. The other is dead silent. Any idea what might be causing this?

Did you try swapping cables to see if it’s related to sub or equipment?

Speakon cables?

You need to see if a sub issue or source issue. So see if the hum follows the gear or the sub. swap left to right sub cables see if hum moves from left to right or right to left

Speakon is a cable used by REL for direct amp connection

Sounds like you did all the right stuff. Are they both plugged into P15? Try one alternate? Have you used the sub previously with no hum?

Yes I know. I was asking if he was referring to spekon cable.

Yes. Both into p15. Ive also tried plugging directly into wall. Not helpful. If I keep the sub powered in and u plug the spekon cable hum goes away.

You’ve done what I would have done to diagnose the problem. However, keep in mind the hum of the sub is like any other ground problem, is will be due to a slight difference in the ground reference of the sub plate amp relative to your power amp. Since you’ve plugged both subs into the P15, one hums, it is possible that cord just isn’t up to snuff or not completely engaged in the socket. I’m talking about the third ground pin. No guarantee that has anything to do with it. But I’d try replugging in the cord at both ends or even try using a different cord. It’s easy to try and costs you nothing one way or the other. Is your 250 plugged into the P15 as well so that you’re sure it is sharing a common ground reference?

I’ve tried using a different power cable and plugging it directly into the wall. Yes. Everything is plugged into the P15.

I had thee same issue with my BHK250 and REL S/5. It was solved by adding a grounding screw to the BHK 250 (provided free by PSA) and a resistor network from REL that connects to that screw and the BHK speaker posts (contact REL or your dealer; my dealer charged $100 for the network but I believe others got it directly from REL for half that). There was a lot of discussion of this topic on the forum some time back. This was with a single sub.

I have 2 REL S/3 SHO subs that exhibited the same behavior. However, running an RCA from the .1/LFE connection on the back of the sub to the BHK Pre RCA input solved it.

Just to clarify, I have the M700 amplifiers, thus it may not be a solution as they are class D amplifiers.

I’m pretty sure I saw your old post and you were getting him when the amp was in standby. This happens when my amp is on.

Already tried that. Didn’t help

In my case (and others on the old thread) the hum was with the BHK250 in standby. Still sounds like a grounding issue, though.

Is anyone using dual Rel subs with a BHK 250? Do I put the black ground wires together to a single point of contact. Right now I have each ground wire going to each screw on the tube door.

I have two REL subs and I ignored the advice from REL and twisted the red and yellow together and hooked them up to the positive speaker terminal on each amp, while connecting the black wire to the negative terminal of each amp. I had the designer of the amp standing next to me when I did this. No hum, no issues. Later I had Analysis Plus make me upgrade cables for my REL subs and they did the same with the cables. Plus and Minus, two cables into the plus Spade.

I have read that this can trash some power amps. But I have also read that such a low level signal passes through to the sub… YMMV.

My amps are also Class D…

Thanks. I was told because the BHK amps are truly balanced I cannot hook the black wires up to the black terminal. It would cause damage to the amp or subs.

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That’s why I mentioned I had the designer of my amps standing next to me when I tried it the first time. I am curious as to how you have the subs and amps plugged into power. That could be the issue?

I followed Rel instructions via this video.

When I had them hooked up previously to an amp that wasn’t balanced I connected as you did with no hum or other issues.

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