JR LPA System

[Gerard]

Amongst various sets of loudspeakers I have, in my bedroom I use a pair of JR149 speakers with the JR LPA and Super Woofer (subwoofer). I have noticed that the LPA unit (Low Pass filter with Amplifier) is no longer working. Does anybody know where I could find a circuit diagram?

What I do know is that the normal left and right channel speaker feeds are fed into the LPA and then looped on to the respective L & R speakers. Inside the LPA, the signals from the speaker feeds are summed and fed through a low pass filter before being amplified and sent out to the Super Woofer. The JR LPA comprises an inut/summing section, a Butterworth low-pass filter (18 dB/octave, -3 dB at 72 Hz, -1 dB at 20 Hz, -45 dB at 2 Hz), followed by a 30 W power amplifer (60 W in a later version).

• http://www.mcmullon.com/icollect/hi_fi/jim_rogers/jr/jr_exa_system_2.jpg shows the system I have;
• http://www.mcmullon.com/icollect/hi_fi/jim_rogers/jr/jr_exa_system_3.jpg shows the more powerful version, which takes the L & R signals from before the main power amp

I would like to have some more information on what is inside the LPA before I attack it with meters and hot pointy things. Failing repair, how would people suggest I implement it today, say with a modern power amp IC?

 

[abbey road d enfer]

I'm afraid you'll have to trace the circuit yourself, since googling JR LPA gives zero valid hit.
You'll have to use troubleshooting 101, does the pilot light lights, are the rails more or less OK, where does the signal gets lost after the input, blah blah...

 

[Gerard]

That's what I was afeared of. I had done a Google search already (and some years ago, when I first bought it).

Oh well, as you say, time to trace out the circuit. At least I now have an idea what I will be looking at; I hadn't found those brochure links when I first looked, back in 2006 or '09