Balanced power amp and subwoofer connection.


Can any one tell me how to connect a powered sub to a balanced Pass amp. I understand that there is a issue with ground which means normal connection using a three wire Neutrik Speakon connection cannot be used. I know as I had damaged a Pass amp and a sub some years ago by following the instructions given to me by a the sub manufacturer ( MJ acoustics )telling me to connect the three speokon wires to the speaker posts on the amp. I took their advise as I assumed a sub manufacturer would know!

Pass are very vague and say I should contact the sub maker and the sub maker say I should refer to the amp maker!

Anyone done this and know the safe method? Can an av and hifi amp be connected to one sub designed for Hifi and home cinema amp connections at the same time. Or should this be for one reciever with stereo and hifi capalities?

Thank you
So is it a MJ acoustics sub? What model? Also which Pass?
no, it a BK electronics, UK made, sub and XA30.5 power amp.

The MJ one was damaged and disposed of. Their quote for repair was too high and when I declined to have it repaired, they refused to send it back to me unrepaired and threatened legal action claiming I would try to sell it on an auction site as new which of cause is crazy. One call from my legal adviser had the dead unit back in two days. A very nasty company ! The unit was personally disposed of at a recycling centre.

Connect the red Speakon wire to the red output terminal of the right channel on the amplifier.

Connect the yellow Speakon wire to the red output terminal of the left channel of the amplifier.

Connect the black Speakon wire to the binding post on the rear of the amplifier that is labelled "ground" or "signal ground" or something similar. DO NOT connect the black wire to either of the black speaker output terminals of the amplifier.

This assumes that you are using just one sub, rather than a separate sub for the left channel and for the right channel.
Can an av and hifi amp be connected to one sub designed for Hifi and home cinema amp connections at the same time.
Looking at the manuals for a couple of the BK subs, it appears that some or all of them are designed to accept high level (Speakon) and low level (RCA or XLR) connections at the same time, with independent gain controls being provided for the high level and low level inputs.

You should not, of course, connect the high level outputs of two amplifiers at the same time, or damage will result.

If the sub provides both RCA and XLR low level inputs, I would also avoid using both of those low level inputs at the same time. I doubt that damage would occur, but depending on the specific design sonics may be adversely affected.

-- Al
Hi. Thanks for that, much appreciated.
I would just drive it via the preamp........
Oddiofyly, would you let me know how the connection can be made using the pre. It has one set of XLR output ( in use in my case) and a set of RCA. Do I connect a single lead from one of the RCA outputs? Would the volume still be controlled? Thanks
There are some issues that would have to be considered before driving the sub from the preamp.

Most or all of the BK subs have line-level input impedances of only 10K. The input impedance of your power amp is 30K balanced and 20K unbalanced.

If you use a pair of balanced y-adapters to drive both the power amp and the sub from the preamp's XLR outputs (assuming the sub provides XLR inputs) the preamp would see a combined load impedance of (30 x 10)/(30 + 10) = 7.5K. That is too low a value for some preamps, especially some tube preamps, to drive without sonics being adversely affected. Which preamp are you using?

If instead of using balanced y-adapters you drive the sub with the preamp's RCA outputs (assuming those are main outputs, not tape outputs which would not be volume controlled), and if the preamp does not drive those outputs from an output stage that is independent of the output stage driving the XLR outputs, the balanced signal path to the power amp will become significantly unbalanced (as well as possibly becoming excessively loaded), probably affecting the sonics of the signal path to the main speakers.

In any event, although opinions and experiences differ, many people consider it to be preferable to drive a sub from the power amp outputs, so that the sonic effects of the power amp are reflected in the signals that are received by the sub as well as by the main speakers.

-- Al
Unless your speakers are full range or almost full range (capable of producing clean bass at the level you desire), you should insert a bass management controller between the preamp and amp. It will provide a subwoofer output. Your speakers get a break, as well as, your amp.

The argument about using speaker level connections to preserve the character of the power amp only makes sense for passive subwoofers.