REL subs with Rowland Amplifiers

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.

Not sure that the REL person is realizing that the inputs of your amp are transformer coupled, and the amp’s descriptions at the JRDG website and in the manual state that "transformer coupled input circuitry provides universal component compatibility and virtually eliminates ground loop noise..."

So it seems to me that due to the isolation the input transformers presumably provide it is likely that connecting the sub’s ground to the preamp’s ground, via the LFE or whatever, will not result in an effective connection between the sub’s ground and the amp’s ground, which is what matters. On the other hand, though, I suppose it is possible that an adequate ground path between the sub and the amp could be formed via that connection in conjunction with the AC safety ground wires in the power cords of the preamp and the amp, which ultimately connect the chassis of the preamp and the amp together.

In any event, given that none of us have much familiarity with how grounds are handled internally in these designs it’s worth a try. And I don’t think it could do any harm to give it a try; just be alert to the possibility of a loud hum. IOW keep the sub’s level control at a low setting when you begin the experiment.

Best regards,
-- Al

I should have mentioned at the beginning the most frustrating thing about this situation is my dealer is a REL and Rowland dealer. He has the ability to connect the REL to the exact amp and preamp that I have, but he won't. When I told him about my situation, he said that he would connect the REL to the Rowland 625 S2, but to date he hasn't.

The other frustrating thing is trying to find out the truth regarding the sound quality difference between the high-level and low-level input.  During a telephone conversation two days ago a REL representative told me there wasn't a difference in sound quality between the two inputs, but the high-level input helps facilitate a better blend between the sub and speakers. Yesterday, a different REL representative sent me this via email... Low level input is about 80% of the high level input. If both inputs offered the same sound quality I wouldn't worry about the high-level input anymore. 

 @ricred1  I think the blend is where it’s all at. The fact that the subs take their signal directly from the amp in the high level set up is what has distinguished REL’s for me over the years. REL used to claim that this was allowing the sub to more carefully track the signal at the amp end, not sure if they still claim that anymore. 
Your dealer is possibly wondering how to connect the sub ground wire to the amp chassis...as unlike many other amp manufacturers, Jeff chooses not to include a separate ground connector on his chassis. If you look at Lamm, Pass and others they do include this. Nonetheless, as I said before, Jeff is willing to add this necessity ( which I believe it really is) to your chassis.

I have been corresponding with Justin Magana who is REL’s Chief Engineer. Based on his advice I twisted the red and yellow wires together and connected my REL via the high-level input. The black wire is floated. It worked! I have plenty of output from the sub and absolutely zero hum.

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