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 would have an exceptional performing receiver though. For a full restoration check out QRXRestore.

QRX-7500's sell for around $300+ while the A version sells for around $400+. The QRX-7001 is around $500 and the QRX-9001 around $800-$1000.

SANSUI QRX 7500 Quad 4 X Channel Receiver Amplifier VGC
SANSUI QRX 7500 Quad 4 X Channel Receiver Amplifier VGC $425.00
Time Remaining: 10d 8h 11m
Buy It Now for only: $425.00
Sansui QRX 7500A Quadraphonic Receiver Amplifier LED Upgrade Serviced Awesome
Sansui QRX 7500A Quadraphonic Receiver Amplifier LED Upgrade Serviced Awesome $475.00
Time Remaining: 3d 19h 49m
Buy It Now for only: $475.00
Vintage Sansui QRX 5500 QRX 6500 QRX 7500 front LED lamps bulbs lights
Vintage Sansui QRX 5500 QRX 6500 QRX 7500 front LED lamps bulbs lights $44.58
Time Remaining: 4d 7h 51m
Buy It Now for only: $44.58

 

Pioneer SX-D7000

In 1980 Pioneer introduced the Pioneer SX-D7000 and made a statement that it was heading into the digital future. It's similar in many ways to the SX-3900 except that Pioneer did away with nearly all of the knobs - replacing them with push buttons. There are no analog meter or dials either as Pioneer utilized their Fluroscan technology for the power meter and digital tuning display. The SX-D7000 retailed for about $800.

 

Aesthetically it's a beautiful receiver. It has a modern, clean look to it and the symmetrical layout of the controls give it balance to the eye. It's rated at 120 watts per channel and 0.005% total harmonic distortion.

 

 

The power output and tuning meters are Fluroscan and the Treble and Bass controls are adjusted via sliders with 11 click stops. The Adaptor switch allows the user to patch in a signal processor such as a graphic equalizer or reverb unit.

 

 

The SX-D7000 was the bigger brother to the Pioneer SX-D5000 and was slightly bigger and a little heavier. Pioneer also added  a C speaker switch, Tone on/off control, a display dimmer and a second phono input. The SX-D7000 was one of the first receivers to incorporate a preamp section that could handle both a moving magnet and a moving coil cartridge. The user could switch between cartridges with the push of a button just to the right of the volume knob. Switching to the MC position boosts the phono gain by 20dB and reduces the impedance to 100 ohms.

 

 

The SX-D7000 also features:

  • Non-switching DC power amp design
  • Quartz PLL Synthesizer Tuner
  • 6 FM and 6 AM station memory for easy tuning
  • High Gain FET phono equalizer
  • Attenuator type master volume control

To set the memory for a station you tune to the station using either the autoscan or manual scan and then push the memory along with one of the station call buttons.

 

Pioneer SX-D7000 Ad

 

The power amp is a Direct Current configuration. Coupling capacitors are used at the input of the amp to safeguard the circuits and speaker systems. Ultra-low-frequency signals which might be picked up from a warped record can cause annoying Doppler distortion in drivers, adversely modulating the audible frequencies. Pioneer's DC configuration removes signal-delaying capacitors from the negative feedback loops to reduce phase distortion. This contributes to a "sharp and densely-textured sonic imagery in the final reproduction".

 

 

Pioneer avoided the problems associated with Class A or Class B amps by designing a special circuit they called Vari-Bias. According to them it is:

"An inspired breakthrough that led to the Pioneer Vari-Bias circuit, which constantly monitors the amplitude of incoming signal, then automatically controls the amount of bias fed to the power transistors. While they 'rest' during no-signal periods they get only a trickle - just enough to keep them from switching off. Actually, this circuit is so simple it does not limit the transient response of the transistors in any way."

The Pioneer SX-D7000 has three power transformers. One is toroidal, for the non-switching power amp, and the other two are of conventional design.

It has three speaker outputs as well as two Phono inputs and one Aux input. It even has an AM Stereo out.

 

 

The SX-D7000 is the beginning of the end for silver faced receivers. It wasn't long after its introduction that audio manufacturers, including Pioneer, moved toward cheaper black plastic components. The receiver has a distinct look to it that some like and some don't. It's still very popular for its performance level can usually be bought for a reasonable price. In good serviced condition they will sell for $500 to $600.

Vintage Pioneer Stereo Receiver Model SX D7000 Rare Mint Condition
Vintage Pioneer Stereo Receiver Model  SX D7000 Rare Mint Condition $1,000.00
Time Remaining: 3d 19h 12m
Buy It Now for only: $1,000.00
Original Pioneer awh 097 B Power Amp Assy For SX D7000 Receiver UNUSED NOS
Original Pioneer awh 097 B Power Amp Assy For SX D7000 Receiver UNUSED NOS $186.69
Time Remaining: 23d 8h 21m
Buy It Now for only: $186.69
Original Pioneer Power Amp board parts for SX D7000 receiver g162
Original Pioneer Power Amp board parts for SX D7000 receiver  g162 $185.99
Time Remaining: 19d 12h 42m
Buy It Now for only: $185.99

 

 

 

 

 

 

 

 

Do NOT follow this link or you will be banned from the site!
Scroll To Top