Sansui QRX-6500

This Sansui QRX-6500 was one of Sansui’s early contributions to the quadraphonic genre. It was manufactured from 1973 until about 1975 and produced 33 watts per channel into 8 ohms when all four channels are driven and 37 watts per channel when each channel is driven. It retailed for $750.00 and has a very distinguished design. The gold/silver front panel fits nicely with the blackout dial window and green and amber lighting. Stick all this in a nice walnut finished solid wood cabinet and you have one very nice looking receiver.

The QRX-6500 has three main features; the QS 4-channel Synthesizer and Decoder, the 4-channel, 280-watt integrated amplifier section, and the super-sensitive stereo FM/AM tuner. Basically, Sansui took what they had developed in the earlier QR-6500 and improved upon it.

At the time their new QS regular matrix system with vario-matrix circuitry was the most advanced method of reproducing a sound field in 4-channel. The QS synthesizer could transform a regular 2-channel signal into a rich 4-channel output. This meant that user’s 2-channel stereo records were still usable on the quad receiver and quadraphonic records were not mandatory. Still, to get the most out of the QRX-6500, using QS encoded 4-channel recordings was recommended.

The QS regular matrix decoder could decode any QS encoded four channel signal. This would work with any encoded records, tapes or even FM broadcasts.

Specifications:

• Tuning range: FM/AM
• Power output: 33W/ch into 8Ω (quadraphonic)
• Frequency response: 30Hz to 30kHz
• Total harmonic distortion: 0.5%
• Damping factor: 30
• Signal to noise ratio: 70dB (line)
• Channel separation: 45dB (line)
• Speaker load impedance: 4Ω to 16Ω
• Dimensions: 536 x 181 x 362mm – 21 3/16 x 7 3/16 x 14 5/16 inches
• Weight: 22kg – 48.5 lbs

As I mentioned above, the tuner on the QRX-6500 is excellent. It utilizes three dual gate MOS FET’s and a precision four gang variable capacitor. Visually it has a lighted dial pointer and meters for both signal strength and tuning.

Sansui’s 4-channel Synthesizer/Decoder Control, a five-position rotary control located on the right side of the front panel, enables the selection of two different QS Synthesizer modes (Surround and Hall), two QS regular matrix modes (Surround and Hall) as well as the additional Phase Matrix mode for decoding SQ records.

The QRX-6500 is not for the feint of heart when it comes to repair or restoration. The 4-channel circuitry is complicated and makes for a crowded interior. Keep that in mind if you find one. It will most likely need some maintenance or repair which can get expensive fairly quickly depending upon what needs to be done.

Look at all the speaker outputs on the back panel! The QRX-6500 could be connected to up to five sets of speakers. There are also an amazing number of inputs for both 2-channel and 4-channel sources. There is even a de-emphasis switch – a vestige of the time when radio broadcasters were going to broadcast with Dolby noise reduction. Not so useful today. There are also three AC outlets on the back panel, one of which is controlled by a front panel switch.

The Sansui QRX-6500 is a beautiful quadraphonic receiver and has a solid place in quadraphonic history. However, unless you want to dabble in 4-channel audio you may be better off sticking with one of Sansui’s 2-channel offerings. If you want to play quad source material then you could also look at Sansui’s later QRX-X001 series which is excellent.