REL subs with Rowland Amplifiers


I'm having issues connecting my REL Carbon limited subwoofer to my Jeff Rowland 625 S2 amplifier via the high-level input. I connected my sub according to REL's instructions...yellow lead to positive on one channel, red lead to positive on the other channel, and floating the black wire(ground). I get minimum output when connected according to the instructions. When I use the low level input, the output is sufficient and the sub sounds great. Per my conversation with Jeff Rowland I need to ground the black wire by loosening a screw on the amplifier and connecting the black wire, but if it isn't properly grounded I may damage my amplifier. Is there anyone that owns a REL with Jeff Rowland 625 S2 amplifier or other balanced differential amplifier? If so, how do you connect your REL via the high-level input. Is there an easier way to ground the wire than unscrewing the screw on my amplifier. I just don't want to unscrew the screw and prefer another method of grounding the sub.   
ricred1
Wow! Congratulations.

So are you saying, then, that the only difference between what worked and what previously didn’t work was twisting the red and yellow wires together, while having exactly the same connections in both cases? If so, I have no idea how to account for that.

Or are you saying that the red and yellow wires are now connected to the same positive output terminal of the amp, while you wait for the second sub to arrive which will be connected to the positive output terminal of the other channel? If so, it would still be hard to explain why you were previously not getting proper results, with the red and yellow wires having been connected to the positive output terminals of different channels. But it would suggest that previously the outputs of the two channels were somehow being subtracted from each other rather than summed. In other words, a polarity inversion was somehow being introduced on one channel, either in the sub or the amp or in one of the connections between the two. Or perhaps as a result of a miswire in one of the XLR cables upstream of the amp, such that pins 2 and 3 are interchanged at one end of one cable. Although most of those possibilities (aside from an issue within the sub or in its connections to the amp) would have had dramatic negative effects on what you were hearing from the main speakers.

So I’m completely puzzled at this point.

Best regards,
-- Al

Ricred what sub are you upgrading from and what improvements are you hearing with the Carbon limited? I have an S5 SHO. Congrats on your purchase! 
Al,
"So are you saying, then, that the only difference between what worked and what previously didn’t work was twisting the red and yellow wires together, while having exactly the same connections in both cases?" YES

"Or are you saying that the red and yellow wires are now connected to the same positive output terminal of the amp, while you wait for the second sub to arrive which will be connected to the positive output terminal of the other channel?" YES, per my conversation with Justin that's the way I have to connect dual REL subs anyway; therefore there wasn't any risk in connecting the single sub this way. He assured me nothing bad would happen, so I tried it. 
chazzzy007,
Thanks.

"Ricred what sub are you upgrading from and what improvements are you hearing with the Carbon limited? I have an S5 SHO." I had a JL Audio F112 v2. The REL Carbon Limited totally disappears compared to the JL Audio F112 v2. I'll make more comments in a couple of days.

@ ricred1 that’s why I asked if your amp was class d. I knew that had been an issue.  As you know I’m a huge fan of rel subs. I think they are the best. I hope you can get the connection you need.