2. amps-preamps
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Balanced power amp and subwoofer connection.

Hello.

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
james123
oddiofyl's avatar
oddiofyl
3,811 posts
 
I would just drive it via the preamp........
james123 OP
61 posts
 
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
almarg's avatar
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almarg
9,670 posts
 
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.

Regards,
-- Al
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