REL subs with Rowland Amplifiers

Thanks, I will send them a email.

As a point of information, for a great many years prior to the introduction of many of their current models, REL manuals recommended that when connecting to amplifiers whose outputs are balanced or bridged that the black wire be connected to a chassis screw.

That should have and apparently did work well in most cases, although not quite all. An exception being a few amplifier designs in which chassis and circuit ground are completely isolated, in which case the result of doing that would probably be a large hum. Another special case involved some long obsolete early class D designs which had very high DC voltages (something like 24 VDC if I recall correctly) on both their plus and minus output terminals, relative to ground, and therefore required blocking capacitors between the amp outputs and the sub.

I don’t know what the reason may have been for REL to abandon that long-standing recommendation of using a chassis screw when connecting to balanced or bridged amplifier outputs, and now recommending that the black wire be floated.

Best regards,
-- Al

Al,

Do you think grounding the black wire to the chassis of my 625 S2 will result with proper output of the subwoofer?

Yes, I would think that to be highly likely.  Given what Jeff has told you, given that REL's recommendation has up until recently been to do that, and given my technical understanding of the situation.

Best regards,
-- Al

I just received a call from REL. They said I could ground the sub/amp by going from the REL's LFE to my Rowland Corus preamp while leaving the black lead floating.