Wiring a subwoofer to monoblocks

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

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

I do not believe the Audiopax are balanced.
As the spec it's two 15 watt amps wired in series to give 30
so I should be ok.

I suspect that is not correct, Simon. It may or may not be balanced in the sense of processing out-of-phase differential signals through its internal signal path, but the fact that the secondaries of its two output transformers are apparently wired in series tells me that the two output terminals are most likely balanced (with neither being at ground potential).

In any event, as I indicated above, no harm can come from trying it with sub black connected to amp chassis (or to preamp chassis, as Hevac suggested). Just don't connect sub black to amp black unless you are totally certain that amp black does not have a signal on it.

Regards,
-- Al