Sansui QRX-7500

Sansui QRX-7500 Front

In the early to mid 1970’s Quadraphonic sound was just coming to the forefront. Sansui was one of the leaders of the 4-channel movement with their QR line of quadraphonic receivers. Around 1974-1975 they introduced the QRX line which included this beauty, the Sansui QRX-7500. The QRX-7500 was the top of the line at the time in terms of power output at about 30 watts per channel (4 channels into four 8 ohm speakers).

Sansui QRX-7500 Meter

The receiver features a built in CD-4 album decoder, SQ decoder (phase matrix), QS decoder (regular matrix), two phono inputs, and outputs for two sets of four speakers.

Sansui QRX-7500 Knob

What’s the difference between the QRX-7500 and QRX7500A? Well, it all has to do with the decoding.

The QRX-7500A was a “hybrid” unit as Sansui moved from the discrete component vario-matrix decoder circuits to their custom Vario-matrix IC’s that were used in the QRX-7001/8001/9001. There were two distinct ICs. The ‘decoder’ IC and the ‘control’ IC which enhanced the separation and decoding ability. The QRX-7500A has the decoder IC but not the control IC. The later receivers had both.

In all there are three variations of decoders built into the Sansui QR/QRX series over their entire production period. The QRX-7500 utilizes the basic QS decoder as originally designed. It’s sometimes called an “RM” or regular matrix decoder. The basic decoder is capable of 3-12db of inter-channel separation. The QR series receivers, the QRX-4500, QRX-5500 and QRX-6500 also have this early decoder design.

Sansui QRX-7500 Lamps

With the QRX-7500A Sansui introduced the partially developed vario-matrix decoder circuit containing two of the three custom ICs required for full Vario-Matrix decoding. The circuit performs similarly to the ‘basic’ decoder mentioned above because the missing ‘control’ IC is the biggest factor in increasing inter-channel separation and this design doesn’t have it. This decoder is capable of 3-12db of inter-channel separation. So, the QRX-7500A has the newer IC designed circuit but lacks the full Vario-Matrix capability of the later design. The Sansui QRX-5500A and QRX-5001 have the same design.

The fully developed Vario-Matrix Type A design with all three IC’s was used in the QRX-6001, QRX-7001, QRX-8001, QRX-9001, QRX-777 and QRX-999. The QSD-1/2/1000 decoders also have the Type A decoder. The Vario-Matrix Type A decoder was limited by design by Sansui to 20db of inter-channel separation, though, in theory, Sansui claims that it is capable of infinite inter-channel separation.

Sansui QRX-7500 Inside

The slightly later QRX-7001 is the improved version of the QRX-7500 with the better decoder circuit as well as a beefier amp section. The QRX-7001 produced 35 watts per channel in Quad mode.

Sansui QRX-7500 Back

The Sansui QRX-7500 is a great quad receiver. It has its limitations given the early decoder design and some issues with solder joints on the circuit boards but overall it is a good performing unit. The QRX-7500A may be a better choice since it has the IC decoder design but if you really want a great decoder then you’ll want the QRX-7001, QRX-8001 or QRX-9001. Expect to pay a premium for those however. Any of these units would most likely need a restoration and perhaps some modification which isn’t cheap. Once done you will have an exceptional performing receiver though. For a full restoration check out QRXRestore.

Available on Ebay

Spread The Love

5 thoughts on “Sansui QRX-7500

  1. Thanks for the very informative article. Is the Sansui QRX-777 the same model as the QRX-7001. I am a recent convert to quad.
    I currently use a Lafayette SQ-M decoder for my quad albums with a Harmon Kardon PA 2400 amp for the front speakers and a monster Hitachi SR-2004 for the rear speakers. Would the Sansui QRX-777 be an upgrade to what I currently have?
    Any advice you can provide would be appreciated. Thanks.
    Rick

    1. Yes, I believe the QRX-777 is the European version of the QRX-7001. They should essentially be the same perhaps with the exception of a voltage selector on the QRX-777. As for the upgrade I’m not sure but Sansui utilized a very good QS decoder for that model. And, of course it can decode SQ, QS, and CD-4. The QS synthesizes the quad sound from stereo LP’s too, which is a bonus.

Leave a Reply

Comments are manually moderated and may not show up immediately after posting. As long as they are not spam they will show eventually. No need to repost.

Your email address will not be published.