BHK Pre and Power on the Way - REL Subwoofer Question


If my preamp has a ground connection could I ground the black wire to that?

I have no issue turning off the sub other than I thought I read the designer said it takes days for the amp to reach optimum state. I wouldn’t want to start from scratch again every time. On the other hand if it needs only 20 minutes or so of warm-up, that’s a different matter…



Sure. It doesn’t have to be a power ground since there;'s no current running through it.


I’m reviving this thread in case anyone is still getting hum with a REL subwoofer connected to a BHK 250. I recently acquired a REL S/5 SHO and got the loud hum when the BHK went into standby, as others have reported. The solution was a combination of the PSA chassis ground (a small binding post that replaces a screw on the back panel), which PSA provides for free, and a “resistor network” from REL, for which they charge about $100. The network looks like a pair of Y-cables that connect each of the left and right sets of binding posts to the chassis ground. No more hum in my case.


Thanks. I started this thread, and in the meantime I got speakers that sound better with no sub…so my T7i is in another system now. But, I’ll check out the “resistor network” for when the sub gets paired with the BHKs once again.


Paul - I just installed the REL BHK network & PSA post and it solved the “hum” issue. With the PSA BHK AMP in standby and the REL subs “ON”; no hum. Once I installed the network, I’ve heard zero hum at any time and it was pervasive. I woke up one morning and could here it at my music room entrance with the AMP in standby. However, once I turned “ON” the PSA BHK250 AMP, “hum” went away. Also, a big word of caution; please read the REL manual on installing the REL GND wire on a balanced AMP (PSA BHK250). You can cause permanent damage (blow an input resistor) to the REL amp if you don’t allow the REL sub GND (black) wire to float (not connected). If you find you have “hum” even if you have followed the manual (page 13); then buying the REL network is a good idea. If you are a DIY type (cheap-skate) type person, below I’ve measured the network resistors and buying (4) 10% 1K resistors and some spades is about $5.00. REL charged me $50 and I thought that was reasonable for 30 min of work and some components. They’re just looking to recoup their staff’s labor and PSA just sent the post for free with instructions. This is an easy fix.



Hi Richard, I just bought a REL and PSA is sending me the binding post. I was planning to ground the black wire to the binding post. Is this different from what you tried? Also, did the REL network come with instructions on how to install? Thanks!!!


wakethetown - The REL network did not come with installation instructions; the PSA chassis GND lug came with instructions. The installation you propose would be different than how I installed the sub wiring. I don’t understand your intention of buying a REL PSA BHK resistor network if you were going to attach the REL sub GND (black wire) to the PSA chassis GND post? I assume the black wire you mention is the REL sub black wire? If I were you, I’d ask REL to send a diagram or instructions on wiring their network to make sure I wired it correctly. You are wiring (2) amplifiers together; want to make sure the connection is proper. I read above toddcc1 hooked up the REL sub black wire directly to the PSA BHK (-) output. The REL manual (S3/SHO; page 13) specifically indicates floating the REL sub black wire. If you connect the REL sub black wire to the PSA BHK amp (-) output without the REL resistor network installed, you can damage the REL sub amplifier. However, the REL manual does not say to buy the REL resistor network if you own a BHK AMP. Their website mentions different amps wiring configurations in the “How To” section; however, the PSA BHK amp is not mentioned. I found this REL solution while in the process of deciding to buy a REL sub talking to John Hunter in emails. He mentioned REL engineers worked with PSA engineers, arriving at a solution for “hum” while the PSA BHK amps are in standby (output switched open), and the REL subs ON. The REL sub GND will now have a path to PSA BHK amplifier chassis GND while the PSA BHK amp is in standby and its outputs open. This path, (2) 1K ohm resistors in parallel, connected to PSA BHK chassis GND (chassis post) would assume the (2) PSA BHK (-) posts are connected together inside the PSA BHK amplifier. This connection will result in providing a 500 ohm path from the REL GND (black wire) to the PSA BHK amplifier chassis GND.

Hope this helps,


YThanks, Richard. I was going to try the PSA/free option first. Yes, the black wire I was referring to is the supplied REL nuetrik speaker cable. I’ve wound it around a screw in the back of the BHK 250 to eliminate buzz while the amp is on.

I also experience a much louder hum when the amp goes to standby. It’s not much of a pain for me to manually turn the sub off first. However, I’m interested in a more elegant solution such as the one you describe. I’m a social scientist, not an electrical engineer so my understanding of circuits is quite limited. I can follow instructions, just don’t really understand the physics behind it.

I must say for all the sophistication of high end products produced by companies like PSA and REL, I’m surprised how “unfinished “ many of the solutions are. To me, it’s equivalent to the days when you had to get out of the car to crank the engine or the early days of personal computers when you had to know command line programming to make it function.


wakethetown - Please read my email again; digest the email, then read it again. The REL sub GND (black wire) is not connected (floating) according to S3/SHO manual (page 13); unless you have the REL/PSA resistor network connected. If you have bought that network and have a BHK amp, the REL GND (black wire) gets connected to the BHK250 (-) post. I connected my L/R REL GND to the bottom (-) and RED & YEL to the bottom (+). If you read my last sentence, you are connecting 500 ohms from the BHK250 (-) posts’ to the BHK250 chassis GND. There would be no need for the REL/PSA resistor network if the solution was to connect the REL GND (black) wire directly to BHK250 chassis GND. This is not electrical engineering, it is logical. This REL/PSA solution provides the PSA BHK balanced differential amplifier (-) output a reference to chassis GND through a 500 ohm resistor. When the AMP is in standby the PSA BHK amp output is open allowing the REL GND (black wire) a path to the PSA BHK chassis GND, preventing the “hum” heard when the AMP is in standby.

Also, in REL’s defense, there are a lot of amplifier configurations: class A/B, D, non balanced, balanced, mono, stereo… As a designer I have seen situations where I thought I covered all the customers configurations to find out I missed one.

I hope this helps,


The instructions that came with the REL network for my S5/SHO and BHK 250 and for the PSA binding post did not say to connect the black wire. Mine floats and I have no hum.


Stevem2 - Thanks, my REL network did not come with instructions. I connected the network as indicated above and I have no hum. It’s odd REL would say to float the sub black wire and connect the network. In the S3/SHO manual (page 13) REL says float the black wire. The manual never says anything about a REL/PSA network. If you are going to float the sub black wire, what is the point of connecting the REL/PSA network. I will talk with REL to make sure I have hooked it up correctly. Hooking up the sub black wire after installing the REL network solved the hum I got when I put the BHK250 amp in standby with the REL sub ON.

Thanks for your feedback,


It’s been a while but as I recall the network instructions just showed how to connect the network and the PSA binding post instructions just showed which screw to replace with the post. Since the REL manual said to float the black wire, that is what I did, and it worked. I can’t tell you network works, or what the black wire does for that matter, as it’s all a mystery to me.


Stevem2 - To me I looked at it logically without REL sending me directions. What is the point of a REL/PSA network attached from from PSA BHK (-) posts to PSA BHK chassis post, if you leave the REL sub GND (black wire) floating. It made the most sense to connect the REL sub GND (black wire) to the PSA BHK chassis GND (post) through (2) 1K (10%) resistors in parallel (500 ohms equivalent). I will find out soon from REL or Paul can answer this post. In addition, I had “hum” when the REL GND (black wire) was floating as I placed the PSA BHK amplifier in standby. As I indicated, I could hear the “hum” from the music room enternace. Some feedback indicates floating the REL GND (black wire) sometimes works without resorting to the REL/PSA network. In my case, the network solution worked fine and have yet to hear any “hum” and it was pervasive floating the REL GND (black wire) initially. So pervasive, I turned OFF the subs till I connected the REL/PSA network.

Paul - Do you have an answer to this conundrum? I appreciate PSA sending me directions on the PSA BHK AMP chassis post connection; wish REL sent directions.



I’ve got a BHK 250 coming my way in the next week or so. I currently have a pair of M700’s hooked up to my Rel 328 sub with the floating ground technique. Works great.

Just to understand correctly, there’s currently no real full proof elimination of the hum problem when the amp is in standby mode? An adaptor from PS might work or a connection kit from Rel (which I searched and couldn’t find on their website) or a combination of the two.

I have a P5 regenerator so I could remotely shut it off from there but I also use this sub in a separate home theater application with the low level input from a receiver. Right now, as always, I’ve just left the sub on 24/7. I’d like to continue to do this.

Any new news or recommendations from the forum.


@Shawn_Costello - I have a BHK250 w/ pair of REL S3/SHO subs. I had hum till I added the REL network & PSA adapter. I have not heard and hum since then. As indicated above in the post I responded to will show you the solution.


What’s the difference between the Baseline Blue connector and the standard Neutrik that comes with the sub? Not looking forward to a $450 purchase to get rid of some hum. I might have to just get off my ass and turn the sub on and off for awhile, life’s first world problems.


@Shawn_Costello - Baseline Blue cables do not get rid of hum. The PSA adapter and REL network get rid of the hum. I bought AC5 1.5m power cables and Baseline Blue cables for the subs after I solved the hum. The REL network was $100 and PSA adapter is fee.



Before you go buying any add-on devices try hooking the REL up to the 250 normally and if it hums then connect the black wire to a ground on another piece of gear even if you have to make an extension for the black wire.


I tried the screw that PSA sent me. It still hums. I might try the extension advice. It’s only a minor annoyance since I manually turn off the sub when I’m done with a listening session. I might eventually get tge REL network to solve the issue.


Are the REL’s that are humming with the BHK amps using Class AB amps or Class D amps? My two Rythmik subs are hooked up speaker level to the 250 and do not hum but they have Class AB amps. When I used an IcePower 1200AS based amp instead of the BHK for a couple of months during the summer I tied the two negative leads on the amp end together and then used an extension wire to connect them to a ground lug on a line conditioner. Worked flawlessly. Another option is to connect an RCA cable to an unused input on the preamp and then to the LFE input on the REL with the LFE volume turned all the way down.