Wiring a subwoofer to monoblocks

I forgot to add that mine have an 180 degree reversal switch which flips polarity, yours may also. Select proper setting by ear if it does.

A monoblock amp may or may not be a differential amp. A differential amp is also referred to as a fully balanced amp, or at least an amp having balanced outputs (meaning that the red and the black speaker terminals are both actively driven with signals, and neither is connected to amp ground).

The specs for the Audiopax 88 contain this statement:

ASTAT™ Asymmetrical Series-Twin Amplifier Topology uses two independent amplifier halves per monoblock whose dual output transformers are series connected for 30 watts of RMS output power

I'm not certain, but that leads me to believe that your amp has both speaker terminals actively driven, with neither terminal grounded. It would probably be a good idea to confirm that with the manufacturer or distributor.

In any case you won't go wrong by following the suggestion in the first part of Stan's post, when you get the second sub -- connect both yellow and red of the sub's cable to the amp's red speaker terminal, and black from the sub's cable to amp chassis. Do not connect sub black to amp black or you may damage your amp if it is in fact balanced.

(With one sub) If the mono blocks are together then I suppose that one hot would go to the hot on one amp and the other hot to the hot on the other amp and the ground to the ground terminal or chassis ground on either amp.

I suspect that this may produce a ground loop hum, although there is probably no harm in trying it. Otherwise you'll have to either use line level, or else connect to just one amp (as described above), which will result in just one channel of deep bass information being reproduced by the sub, rather than both channels summed together.

Depending on which version of the Quake you have, there is either a 0/180 phase switch, or a mode switch that provides 0/180 selection, so that will allow you to compensate for the Audiopax's phase inversion. Although depending on placement the 180 position may not necessarily be best -- go by ear as Stan suggests.

Regards,
-- Al

Thanks guys
however the response from Al has me wondering.
I'm in the uk and would have no chance of getting the Audiopax sorted if I have a mishap.
I'll mail Audiopax but from past experience, won't hold my breath waiting for an answer - Where's Jim Smith when you need him :_)))

Simon

I've had 2 different fully balanced amps that I wanted to connect my Rel sub to. 1) Ayre V3 - I called the tech support guys. They told me to connect the ground wire to one of the scews on the chassis. I did and it worked great. 2) PS Audio HCA-2 I sent a request on their tech support forum and was told by Paul McGowan who responded to the post to install a 1Kohm resistor in line with the black wire and the negative speaker terminal (I had tried the Ayre chassis screw trick and it did not work).

Not sure if this info is useful to you, but do know that if your amps are fully balanced don't connect the ground wire to the negative speaker post whatever you do.

If they're not fully balanced and you're only concerned about a ground connection to the preamp, one option is to fabricate a ground strap chassis to chassis.

PS Audio HCA-2: I sent a request on their tech support forum and was told by Paul McGowan who responded to the post to install a 1Kohm resistor in line with the black wire and the negative speaker terminal (I had tried the Ayre chassis screw trick and it did not work).

Good info, and a clever solution if connecting black to chassis does not work (which I think would mean that on that amp chassis is not common with circuit ground).

If that proves to be necessary, with a 30W amp I'd suggest that the 1K resistor be rated for 1 watt (or more), to be sure that the resistor will not be overheated if the amp is putting out high power for significant time AND if a connection somehow exists (now or in the future) between sub ground and amp ground (which would result in significant current flowing through the resistor).

Regards,
-- Al