Stellar S300 amp: hum with REL subs

I am considering the Stellar S300, but I have a REL T/7i sub that states that, when using with monoblocks, multiple subs should be used. I can’t afford two REL’s so I am wondering whether, although housed in one unit, the Stellar S300 considered two monoblock amps for this purpose? Anybody run into this? I do see the description of the S300 states “each of the two channels is a complete and independent power supply and power amplification stage”.

I think this is likely a recommendation from REL, you certainly aren’t required to run dual subwoofers when using mono blocks. We’ve had a number of customers use a single or dual REL subs with the Stellar S300 without any issues. There is a slightly different wiring configuration when using a REL with any PS Audio amp, but that’s more to prevent the unit from humming when the system is powered down. Just let us know and we can walk you through that wiring configuration.

I would appreciate receiving that information. I am getting a hum, and the guidance from REL’s manual states that I should “float” (not connect) the black ground wire. I have set it up this way, and am still getting hum.

Not a problem. In order to get rid of the hum while the system is off, you’ll want to run an unused RCA cable from any un-used RCA plug in the system to an input on the REL. If available, the RCA input on the S300 is perfect for this. Not for signal but instead just to a ground connection.

I have now tried 3 things, without success, to eliminate the hum coming from the REL sub ( because I have gotten 3 different instructions from you, the REL literature, and the local REL dealer):

  1. Floating (leaving unconnected and taped off so it cannot make contact) the black ground wire in the REL wiring bundle. This is the solution stated in the manual for my REL sub for connecting to a class D amp.
  2. Connecting the black ground wire in the REL wiring bundle to an unused RCA connector on the preamp - one of two suggestions from the REL dealer.
  3. Connecting a RCA cable between an unused RCA connection on the sub and an unused RCA connection on the preamp - recommended by both you and the REL dealer.

None of these have worked. When I switch on the sub, without anything powered in the main system, I get hum from the sub.

I get no hum out of the system when I eliminate the sub, so there is no ground loop.

I inquired before I ordered the Stellar 300 and was told it would work with a REL T/7i, but I am coming to believe that isn’t true. Any other suggestions?

I’m surprised the RCA cable still didn’t help. Have you tried connecting the black cable to a chassis screw on the amp. There should be one near the XLR input. Beyond this, you may need to reach out to REL and chat with them. They have a resistor kit that you can install that should get rid of the hum.

Hi Jamesh

As a customer waiting for the M700 to come, i also have a REL T7i sub that works perfectly in my Cambridge Audio amplifier by wiring two Red and yellow wires of REL to two separate red(positive) ports on amplifier main speakers, the single black wire left of REL connect of the one of two black ports on amplifier main speaker. Is that the same wiring for REL sub to new M700 with small change is to connect the REL black wire to the M700 chasis ?

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Per your advice, I have also now tried connecting black wire to chassis ground - also without success. BTW, a specific grounding terminal is now included on the rear panel of the S300 – this doesn’t even appear in the diagram in the manual. In any event, it didn’t work. I’m out of ideas and probably will be returning the amp - don’t want to go the resistor/suppressor route.

Leann -

If I’m understanding, sounds like the T/7i worked well with your Cambridge amp, as it did with the previous amp I had, wiring yellow to Left+, red to Right+, and black to either Left- or Right -.

But the S300 is a class D amp - different from my prior amp and probably from your Cambridge, and the REL has to be wired to it differently. However, I have been unable to make any solution work - including the most recent suggestion of trying to connect the black wire to chassis ground. Don’t know if the M700 is a class D – maybe you’ll have better luck. I think I’m giving up.

I’ve tried 4 configurations and each results in loud hum from the sub - even with the main system powered off. (1) Floating (leaving unconnected) the black ground wire from the REL wiring bundle. This is the solution the REL manual says will work. (2) Connecting the black wire to an unused RCA connector on the preamp. (3) Connecting the black wire to the chassis ground terminal on the S300. (4) Connecting a cable between unused RCA connectors on sub (specifically, “LOW .1/LFE” as well as “LOW LEVEL INPUT”) and unused RCA connectors on preamp.

I had been using the REL without problem with a previous amp, so I know it works fine. Seems like it is incompatibility between the REL and the S300. Unless someone can tell me that they have had success, and how, I think I’m giving up on the S300.

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Try #5 – try floating the ground on your REL power cable or amp power cable. If the hum goes away, there’s a ground loop between the power outlets. solution is to plug both devices into the same strip.

I had a very tiny hum coming from my left subwoofer. Turns out it was a ground loop between my two dedicated 75ft 20a home runs. Go figure.

So anybody here have been successed with REL T7i single sub work with M700 without hum ? what is the method wiring you did ?
thank you

Checking the spec, i see the M700 obviously a class D amp which is the negative pin on speaker ports not grounding to chasis, and the same S300 amp is class D as well, therefore i will be facing the same problem. but there should be a way to get this resolved. just digging the Internet instead

I’ll give it a try, but seems unlikely in that I had my old amp and the sub plugged into the same outlets I am using now.

I find this post and you may give it a try, the way they did for 2 channels class D seem pretty simple that is just connect the red and the yeallow wires of the REL to positive ports (+) ports of left and right on main speakers of the amp, the black wire of REL leaves floating or tape it for not contact to anywhere, then using the RCA cable to connect the RCA low input port on the REL to any unused RCA port on pream, DAC. turn off the volume of Low input port. It should be OK for that wiring. I suppose you are using the high input level port

But i’m not sure the REL Sub will go to standby when main speaker amp feeds nothing to it ?
Can you try and let anybody know teh result? i think lot of people here may have the same issue
here the link of the post

Leean -

If you read earlier in the thread, that is one of the 4 methods I tried already, and it did not eliminate the hum. On the S300, they are now including a ground terminal on the rear panel, which I would think would be a “true” ground (which, as you note, the (-) speaker connection on a class D amp is not). Even connecting to this, however, did not eliminate the hum. I hope you have a different outcome with your M700.

Companies like PS that make audio components must just be cursing REL’s existence.

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No way to firgure out now until i have the M700 and test myself.

SUCCESS !! It was attaching the black wire to the chassis ground that did the trick. I don’t know why it didn’t work when I first tried it, but I decided to turn it back on and was going to try both the chassis ground and running the RCA between the sub and the preamp (but I hadn’t yet made that connection), and when I switched it on … NO HUM !! WOOHOO!! So, yes – the solution is attaching the black wire to chassis ground !!! Thanks Leean – it was your last reply that got me to thinking about trying both things. Cheers and good luck with your M700!!!

Thanks God, i’m the lucky guy, i don’t even have the M700 now and still waiting for it, what i posted is just hoping someone else with their devices can test and experiment themself then it could save my time

Can you please help to check if the Sub goes standby when idle with no feeding from the main speakers ?, the led should go RED when standby as i remembered