Wiring a subwoofer to monoblocks

All sorted, all singing.
For anyone using lowish powered valve amps with speakers
around 89/91dB efficiency, I'd recommend trying a pair of cheap subs before ditching the speakers.

Well this should have been a happy post!
After picking up a second Quake and setting
everything up - sonic bliss.
The two subs were harder to integrate than one, probably due to lack of space limiting their positions I think but the results were way beyond my expectations.
Whilst my amps and speakers were never a match made in heaven, financial constraints meant the subs were my last gasp attempt to achieve the sound I knew the Audiopax could produce.
So after about three years of ownership I achieve nirvana - and two weeks later one of the Audiopax dies:-(
Sometimes I think this hobby is very like the Egyptian Sand dance, two steps forward, three back :-)

Made up cables and hooked up the sub yesterday.
Not expended much energy setting it up but already I'm over the moon with the results and can't wait to pick up another for a matching pair.
Seems to let the amps really sing, opens everything up and
real bass to boot -result:-)
Thanks for everyones input.

Hi All,
nothing is a problem when you know how!
Big thanks to Jim Smith - I have the knowledge,
all I need now are the connectors/cable...
and another Quake :_)))
Will report back when it's hooked up.

Thanks Al,
I really don't want to do harm to the Audiopax as I called in every favour I was ever owed to get them (a nice man on here who will remain nameless).

I hasten to add the reference to Jim was only because I know people who know him and I knew he'd know cause people I know that know,well when it comes to pax or avant garde - he's da man! so I said his name and crossed my fingers:-)
Email on it's way Jim

Rgds to all Simon

'
Simon74 said, "Where's Jim Smith when you need him :_)))"

LOL!!!

Send me an e-mail - jim@getbettersound.com - I can help.
'

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

With my Monoblocks and one REL subwoofer, I have one hot wire (red) to the + speaker post of one amp. The other hot wire(Yellow) to the + speaker post of the other amp. And the ground (black) to the - speaker post of one of the amps (either will do) Sounds great!

Thanks all,
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've seen the resistor idea before.
I'll not be rushing into this in any case, says he feeling
impatience gnawing at his leg:_)
Has brought about some polarisation of ideas on one of the uk sites as some people reckon valve amps (some anyway) can't drive subwoofers/or do bass so the low level input to the sub is the way to go?
I was hoping that the 100 watt amp in the sub would take a bit of a load of the 30 watt amps trying to drive 4 Ohm speakers.
My only experince of subs was a large REL Stentor when I was using a Passlabs X-250. I loved it finding it hard to beleive how much it helped across the spectrum.
Then the wife kicked me out of the lounge into my wee cave
and the Pass and the REL were serious overkill:_(

When I had a Rel for the front I connected the Left and right to their terminals, then I connected the common to the preamp. When I tried it to one of the amps I got a loud hum and did not when I connected to the ground tempinal on the preamp.

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

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.

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

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 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.

With 2 Subs it is easy, Both hot to one hot on amp and the ground to ground, either chassis ground or speaker terminal. The other wired the same way. I have 2 Stadium subs wired this way. 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. Sumiko now owns REL as well as imports them, check their web site. There is a guy there who is very knowledgeable and several who aren't. I received two emails containing totally conflicting advice from them last summer. If the monos are far apart I think you will have to use line level or some drastic alteration to the speakon cable. The high level is better.