Ayre amplifier to Subwoofer connections

I believe it will work ok either way, but connecting sub negative to amplifier chassis ground is probably preferable in that it would avoid possible problems or damage if at some point in the future the sub ground inadvertently became common. The minor downside of connecting that way is a 6db reduction in the signal amplitude going into the sub, which most likely just necessitates a corresponding increase in its level setting.

Basically, a balanced output has signals on its two output connectors (or connector pins, in the case of line-level xlr connectors) that are equal in amplitude but inverted in polarity, relative to each other. Components with single-ended outputs (or inputs) have their return connection grounded to chassis. Components with 3-prong power plugs have the ac safety ground prong also tied to chassis.

So if you were to connect the two sides of a balanced output into a single-ended input, and both components had 3-prong ac plugs, you would be grounding one of the two balanced signal outputs. Depending on the design of the output circuit, that could conceivably cause damage.

In this case, that situation is avoided because the sub amp's signal ground is not common with ac safety ground. However, as I say connecting it's ground to amp black would create the risk of damage if the sub chassis inadvertently came into contact (either directly or via a cable) with the chassis of any other component that had a 3-prong plug.

By connecting sub negative to amp chassis ground, the sub input will only see half the amplitude that it would see if it were connected between the two equal but opposite polarity signals that are present on red and black. Hence the need to increase the sub's level setting by 6db, which won't be a problem unless there is a gain or sensitivity mismatch somewhere in the system.

Re your final question, the sub leads should ideally be connected at the amp end of the speaker cables, not at the speaker end. That way the current drawn through those cables by the main speakers, and any consequent voltage drops that might result from interaction of that current with cable impedance, will not affect the signals to the sub.

Regards,
-- Al

So if you were to connect the two sides of a balanced output into a single-ended input, and both components had 3-prong ac plugs, you would be grounding one of the two balanced signal outputs. Depending on the design of the output circuit, that could conceivably cause damage.

To clarify my statement a little further, if both amp & powered sub had 3-prong power cords, the path by which the negative (black) output of the amp would be grounded is: Amp black to sub chassis ground to sub ac safety ground to safety ground pin on sub power plug, then via ac wiring to ac safety ground pin on amp power plug, then to amp chassis ground.

Also, I'll add to my previous comments that another way in which sub signal ground could conceivably become common with ac safety ground is if an internal short were to occur within the sub amp. That is very unlikely if it is well designed, but if a short were somehow to develope between its signal ground and the neutral prong of its 2-prong ac power plug, that would create such a situation since ac neutral and ac safety ground are tied together back at your ac service panel.

Regards,
-- Al

Al,

You are very good at explaining things! you must be a physics teacher or something. I am familiar with how balanced connections work to cancel noise by summing inverted signals. Your explanation has helped me to understand the issue of the interaction with grounds.

Since I have also done home wiring, I also get your point about the possibility of the negative lead going to common ground through a short of the amp.

I think it makes good sense to use chassis ground (per Ayre's recommendation). It is helpful for me to understand why this is so. I don't think the 6db drop will be a problem.

thanks alot Al - I have seen some of your other posts and appreciate your involvement in the Audiogon community.

drew.

the sub leads should ideally be connected at the amp end of the speaker cables, not at the speaker end. That way the current drawn through those cables by the main speakers, and any consequent voltage drops that might result from interaction of that current with cable impedance, will not affect the signals to the sub.

This is as debatable as the long interconnects vs. long speaker cable argument, as there are pros and cons to each approach. While a technical argument can also be made for connecting the sub the speaker's binding posts, simple logistics makes the strongest argument.