What have I done wrong?

I have decided to give the High level connection a go on my UK made BK XXLS 400 sub. I had an email from the makers a short time ago, and was given a link to the REL way of connecting a sub via high level to my PS S 300. I have the Stellar Gain Cell dac/pre connected to the S300 by way of XLR ( as recommended) and attached the wires (red and yellow( to the + terminals I have my front speakers plugged into, and just got a funny noise/ no music. And if I disconnected the sub lead ( that goes to the Anthem a/v amp) I just got a very loud hum… what have I done wrong, it making me a tad pissed

With a class a/b amp you need to attach the black wire to one of the negatives on the amp

Ooop, sorry. S300 is class d, advice indeed is without attaching negative…

Your going to have to attached the Black ground wire to an alternative ground source. If there is a grounding lug on any other piece of gear use it though you will probably have to extend the subs ground wire. I am doing the same thing with my two subs to the BHK 250 which has the same grounding issues as a Class D amp.

I recommend a Forum search with the key words S300, REL and Hum. This has been discussed and solved in various threads on this forum. Roll up your sleeves and dig in, good luck with the search. If that does not work for you ping @jamesh on this Forum and he should be able to assist.


REL offers excellent information on how to properly connect the high level to a variety of amps on their website. In depth with lots of pictures. Try there.


there are quite a few warnings NOT to attach the black wire. I have cut the bare wires off and taped the end, just incase it makes contact

I have, and the video I was given showed me to connect the 2 wires I mentioned to the positive speaker connections and use the attached LFE cable as the ground

One of my BK subs uses high level connections to a Class D amplifier (initially a Sprout100). I did not try to fix the black earth lead to the amp chassis, but instead used the ‘trick’ suggested by REL; you leave the LFE lead connected but turn the volume control for it right down. The LFE lead then provides the earth return to the amplifier. Works fine with no hum for me.


So Chris, was I right to connect the 2 wires (Red and Yellowish) to the terminals the speakers are plugged into. I have the PS dac/pre connected via XLR, that should have no bearing on the subject

That’s what I do!

My BK XXLS 400 does not hum at all. But then it’s not plugged in and only acting as a plinth for a sculpture. The wife wants it to remain for that purpose. I connected my REL using high level wire to Bluesound Class D per REL instructions, no problems.

You’re right to connect the red and yellow to the + terminals. Completely floating the ground will likely cause a hum. If you have one of the more recent S300s, there is a chassis ground for this purpose. Connect the black wire to that ground lug and you should be set. You’ll want to have the amp switched on as well.


I will have a look tomorrow, in the daylight. Thanks