QRX-5001 Preamp Out

[DC__Exile]

Hello. I’m longtime quad but new to the forum and new to tinkering with circuits and schematics. I have a rebuilt QRX 9001 with the holy grail upgrade from qrxrestore in WA as my main system. But for fun I bought a qrx 5001 cheap on eBay. I want to create preamp-out taps on the 5001 so I can use the variomatrix circuit with external power amps. I’ve identified the positive leads for each channel, but I don’t know where to find the respective negative leads (or lead— maybe they share the same one?) off the circuit board. Thank you!

 

[par4ken]

Hello. I’m longtime quad but new to the forum and new to tinkering with circuits and schematics. I have a rebuilt QRX 9001 with the holy grail upgrade from qrxrestore in WA as my main system. But for fun I bought a qrx 5001 cheap on eBay. I want to create preamp-out taps on the 5001 so I can use the variomatrix circuit with external power amps. I’ve identified the positive leads for each channel, but I don’t know where to find the respective negative leads (or lead— maybe they share the same one?) off the circuit board. Thank you!

The negative would just be ground. You could pick it up from any of the input/output jacks but would be best to go right to the board that you are taking the outputs from to avoid any possible ground loop/hum problems.

 

[DC__Exile]

The negative would just be ground. You could pick it up from any of the input/output jacks but would be best to go right to the board that you are taking the outputs from to avoid any possible ground loop/hum problems.

Thank you!

 

[rmorit01]

Interested in your project as I have a QRX 5001. watching so please update - I am always impressed by the sound from it and it performs well in quad with my 4 ohm epicure speakers. Misses some bells and whistles of the big brothers but by my ears it does better across the board than some of my other Sansui quad receivers - plus in stereo it is very strong.

 

[DC__Exile]

Interested in your project as I have a QX 5001. watching so please update - I am always impressed by the sound from it and it performs well in quad with my 4 ohm epicure speakers. Misses some bells and whistles of the big brothers but by my ears it does better across the board than some of my other Sansui quad receivers - plus in stereo it is very strong.

Will do!

 

[barfle]

I know you’ve already found the signals you’re looking for, so this may be redundant information, but I would just take my signals across the volume controls. The signal is on one side and the ground is on the other. The wiper is, of course, a variable level controlled by the knob.

 

[DC__Exile]

I know you’ve already found the signals you’re looking for, so this may be redundant information, but I would just take my signals across the volume controls. The signal is on one side and the ground is on the other. The wiper is, of course, a variable level controlled by the knob.

I actually tapped at the last point on the tone board, which I believe is just after the balance control (still learning how to trace signals on the board). But I committed the ultimate newbie mistake of over-confidence and working with loose boards with the power on. I shorted something bad that’s beyond my ability to trace. It’s not any of the fuses, and all the service manual usual suspects that I can measure with a multimeter were good. So this project is dead for now, but stay tuned.

 

[barfle]

I actually tapped at the last point on the tone board, which I believe is just after the balance control (still learning how to trace signals on the board). But I committed the ultimate newbie mistake of over-confidence and working with loose boards with the power on. I shorted something bad that’s beyond my ability to trace. It’s not any of the fuses, and all the service manual usual suspects that I can measure with a multimeter were good. So this project is dead for now, but stay tuned.

While I feel your pain, fortunately I haven’t had quite that experience in many years. Once you learn how to use an oscilloscope, analog circuitry becomes quite transparent. Good luck, and keep us posted on your progress.

 

[DC__Exile]

While I feel your pain, fortunately I haven’t had quite that experience in many years. Once you learn how to use an oscilloscope, analog circuitry becomes quite transparent. Good luck, and keep us posted on your progress.

I actually have a 7001 to play with now. I know where to tap and what not to do. I’ll work methodically and send photos.