JR Loudspeakers Woofer Amp Model L.P.A.

[Gerard]

Does anyone have a circuit diagram for a JR Model L.P.A. subwoofer amp?

It takes the loudspeaker feeds from a normal stereo amp, combines them into a low-level mono signal (passing the high level signal on to the L & R loudspeakers), passes the low level signal through a low pass filter and amplifies it to drive the JR Super Woofer. As I understand it, the low-pass filter is a Butterworth-type filter, 18 dB/octave, -1dB at 20 Hz and -3 dB at 72 Hz

I bought a pair of JR149 speakers, which came with a JR Super Woofer and and LPA unit. However, the latter seems to have died. I have two ideas in mind:

1. Repair it, or
2. Build a modern replacement, with an adjustable filter and a much more powerful amplifier (the Super Woofer neeeds more power than the LPA provides; the LPA is only 25 W)

Before I open up the LPA again and try to trace out the circuit, I thought I should ask here first, in case anyone has already done this.