Ayre amplifier to Subwoofer connections

Thank you, Al. After i posted my question, I looked around on AA and found a response from a REL representative to a customer in India concerning his hum problem.

Since your Ayre amp is balanced and since you are using two subs, you must have a balanced hi level inupt which your model does not have. It is not a product defect. The unbalanced hi-level input can be used on balanced amps so long as there is only one sub. Also, since the black speaker terminal on a a balanced amp is not ground but rather positive-inverse, you must ground to the chassis, any screw that stops the hum.

Therefore you can use one sub on the Ayre with the sub grounded to the chassis, or perhaps just take the ground from the LFE and leave the black wire out of the equation if that works for you.

If you wish to have two subs on this amp, you must have one of the larger models that are equipped with balanced hi-level inputs. This is, in fact the only circumstance (two subs in stereo on a balanced amp) where the balanced hi-level input is used. This also gets wired up quite differently. Each channel is red-positive, yellow-negative, and black to chassis ground.

This would suggest that I'm SOL regarding using two subs with the Ayre and will need either different models of RELs or a different approach to amplification, such as separates with two sets of preamp outs, or monoblocks, or an unbalanced stereo amp. However, I'm not sure I believe the guy's answer. I have sent a note to REL and will also call Ayre at some point to try to get more clarity.

Drewh1, your response slipped in. Yes, I will call Ayre, good suggestion.

Does anyone know if JL Audio subs present the same dilemmas?

Hmmm (pun intended :)).

I feel quite certain that what I said is correct in terms of basic functionality, but I can't say with certainty that hum won't arise (just as it can arise in any system with unbalanced interconnections).

By connecting the black wires from both subs to amp ground, you are connecting the signal ground of both subs together. If the two subs do not have significant voltage offset between their signal grounds (such as might result from plugging their 3-prong power cords into separate dedicated ac lines), and if their power transformers do not have significant leakage between ac hot or ac neutral and signal ground, I wouldn't think that there would be a problem. Even more so because the signal levels involved are speaker-level, rather than being line-level (at lower voltages).

If a hum problem did arise, conceivably it could be fixed by connecting a heavy wire directly between ground points on the two subs. Or perhaps by using cheater plugs, to isolate each sub from ac safety ground.

That said, both the causes and the solutions to hum problems arising from single-ended interconnections can, as I'm sure you realize, be elusive. If REL answers you similarly to the rep you quoted, I would try as much as possible to pin them down as to whether they are basing that on hands-on real world experience, using their subs with balanced amps, or if they are perhaps just being overly idealistic.

Best,
-- Al

Drewh1, your response slipped in. Yes, I will call Ayre, good suggestion.

Does anyone know if JL Audio subs present the same dilemmas?