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).
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.
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.
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.
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.
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.
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
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.
Yo tengo el sansui qrx 7500 y la verdad su sonido es calido con buena potencia lo uso con unas floorstanding hibridas entre componentes Pionner ,Visaton ,Sony …la verdad q quede muy complacido con este 7500 tomando en cuenta q tengo el Sansui g9000 tambien
Saludos amigos ???????????????????? Sansui
sansui dilawan minggir dulu lainya
do you know a shop here at Phils. that modifies this brand i have a QRX 7500 which i plan to keep for long
I have Sansui QRX 6500 do you have any background on it?
I have a Sansui 7500A and the music it delivers is unbelievable. I have 3 friends who heard the receiver and went out and bought QRX8001s and a QRX6500. The third could only find a 6500 but all are pleased. These machines deliver top quality sound, not delivered by any product today, unless you spend outrageous money.
wow, i had one i bought when i was in USAF stationed in PHILIPPINES in 1973. i think i paid $400 or so then. i wish i still had it. thanks Rich
I have a QXR7500 from 1974. I don’t have the quad disk. It’s Excellent. Music outstanding.