REL subwoofer with old McIntosh tube gear?

Thanks. The Amps are Mc-60s and I've got the REL T-7 wired to the speaker outputs..8ohm/com. I tried jumpering to ground..no change.

The hum is pretty slight but definitely there only when the amps are on..

When connecting a single sub to two monoblock amps REL generally recommends connecting the sub's black (ground) wire to the chassis or other ground point of the preamp. The red and yellow wires would be connected as they apparently are presently, one of them to the 8 ohm tap of one amp and the other to the 8 ohm tap of the other amp.

I would NOT try that, however, without Gnd and Com being jumpered together on both amps. Connecting the black wire to preamp ground, or for that matter to Gnd on one of the amps, without the jumpers being in place would result in the sub seeing a floating input from each amp having no return path to the secondary of the output transformer. The result would probably be a huge hum.

The schematic appearing on the last two pages of the manual may help to clarify that.

Regards,
-- Al

Thanks Al. Are you sating I should jumper both amps from common to ground even though the black wire from the REL is only connected to one?

Thanks very much. I'm assuming there should never be a hum...even a slight one?

I'm saying that if I am correct in assuming that the red wire from the sub is connected to the 8 ohm tap of one amp, and the yellow wire from the sub is connected to the 8 ohm tap of the other amp, then what you should try is connecting the black wire to a ground point on the PREAMP, such as a chassis screw. But you should only do that with the COM and GND terminals of each of the two amps jumpered together.

Regards,
-- Al

Got it...I'll try it. Thanks!