AMP: Sansui QA-5000 Quadraphonic Integrated Amplifier

[Quadrockasaurus]

If you have any more photo's or comments to make on this Quadraphonic unit please feel free to post them in this thread....

Sansui QA-5000 Quadraphonic Integrated Amplifier


Rarity: ULTRA RARE
Average Sale Price: UNKNOWN

​

The QA-5000 Quad Integrated and the identical looking model above it in the range (...the QA-6000) are two of the hardest Sansui Quad units to track down. I've never seen one, and even images of them are hard to find.

From what I can see, the facia appears to be similar to mid-lower Sansui Mid'70's Stereo Integrated's with the Copper/Bronze-ish tinged front panel. The QA-5000 & 6000 share a service manual so I'm guessing they'd be mostly identical inside.

Not sure what "version" of the QS Decoder/Synth was included...but I've seen the QA-5000 alongside the QRX-7001 in a German Catalog on the web..(which I can't locate anymore), so it may be one of the late QS variations.

I've noted that 4x15Wpc (..RMS or Peak not mentioned) was listed as the max power output of the QA-5000 in that old catalog.

 

[QuadMusic]

This arrived this morning for £59 delivered, about $95. It might be a few days before I can have a play with it:

Regards,

Peter

 

[Disclord]

It's interesting how Sansui's QS matrix system was actually an outgrowth of their "Quadraphonic Synthesizer" units that used the bizarre phase modulation across the rear channels. Then they took a license from Peter Scheiber and turned QS into a full-blown Encode+Decode system and a short time later introduced the Vario-Matrix, which, I believe, was the first variable matrix system on the market.

 

[jsrstereo]

It's interesting how Sansui's QS matrix system was actually an outgrowth of their "Quadraphonic Synthesizer" units that used the bizarre phase modulation across the rear channels. Then they took a license from Peter Scheiber and turned QS into a full-blown Encode+Decode system and a short time later introduced the Vario-Matrix, which, I believe, was the first variable matrix system on the market.

Dear Disclord:

Your comment about Sansui's use of phase modulation in the rear channels of their early syntheszer units is very interesting. Can you explain "phase modulation" to this ignorant non-techie?

 

[Disclord]

Dear Disclord:

Your comment about Sansui's use of phase modulation in the rear channels of their early syntheszer units is very interesting. Can you explain "phase modulation" to this ignorant non-techie?

Instead of passing the rear channels through all-pass networks that had a relative 90-degree phase shift, the early Sansui Synthesizers used phase shift networks that differed between channels and with frequency - which caused odd tonal changes and major listening fatigue. It was all in an attempt to squeeze out something sounding like "separation" - if you have an early DTS Neo:6 decoder you might have heard the weird effects caused by non-smooth, rapid phase shifts - the early DTS Neo:6 decoding didn't always do a good job of breaking the signal up into the multiple bands and recombining them after decoding - so you'd hear added sounds that followed instruments or vocals - almost like someone whistling along with the music or a weird fluttery echo. The early Sansui units, such as the QS-1, could produce similar effects. In the brochure for the QS-1, Sansui brags about the phase modulator, so there's no doubt that it's how they intended the unit to sound - it's just too bad it was so awful.

 

[jsrstereo]

Instead of passing the rear channels through all-pass networks that had a relative 90-degree phase shift, the early Sansui Synthesizers used phase shift networks that differed between channels and with frequency - which caused odd tonal changes and major listening fatigue. It was all in an attempt to squeeze out something sounding like "separation" - if you have an early DTS Neo:6 decoder you might have heard the weird effects caused by non-smooth, rapid phase shifts - the early DTS Neo:6 decoding didn't always do a good job of breaking the signal up into the multiple bands and recombining them after decoding - so you'd hear added sounds that followed instruments or vocals - almost like someone whistling along with the music or a weird fluttery echo. The early Sansui units, such as the QS-1, could produce similar effects. In the brochure for the QS-1, Sansui brags about the phase modulator, so there's no doubt that it's how they intended the unit to sound - it's just too bad it was so awful.

Is it correct to say that the early ElectroVoice EVX-4 "Stereo 4" decoder did not use phase modulation?

 

[Disclord]

Is it correct to say that the early ElectroVoice EVX-4 "Stereo 4" decoder did not use phase modulation?

The EVX was a 'real' decoder for the EV-4 matrix, not just a synthesizer for non-encoded recordings, as the QS-1 was. I'm not sure which "version" of the EV-4 matrix the unit was for though - see, at first, ElectroVoice EV-4 encoding/decoding was very similar to the "regular" matrix systems such as QS and RM, but it didn't use any phase-shifting to encode the rear channels - only reverse polarity and L/R blending. So it couldn't encode a "Center Back" signal, only a 270 degree horseshoe. For various reasons, to encode the full 360 compass, quadrature networks (phase shifters) are required, and the 'first' version of EV-4 didn't use them. The quadrature networks used in QS/SQ/UHJ and Dolby Surround all shift the relative phase between the channels by +90 degrees, which is very different than the phase modulation used in the Sansui QS-1.

Anyway, after a short time on the market, CBS and ElectroVoice joined forces and EV-4 was changed (the sequel) to a phase-matrix that used phase shifters, with points on the Energy Sphere that were very close to CBS SQ's encoding/decoding... it wasn't an exact duplicate, but close enough to work and it could now encode the full 360 compass. Unlike SQ's basic, non-logic matrix, EV-4 (the Sequel) used non-complimentary decoding matrices - in other words, the encoding and decoding points were different from each other - so, instead of the -3db separation between Lf and Rf that QS had when decoded, EV-4 gave -6db L/R front separation but it was reduced to only 1db between the rear channels. (in 4:2:4 matrix decoding, whenever separation is increased between a pair of channels, the separation is decreased between the opposite pair of channels. The maximum 'all around' separation you can ever achieve without a logic decoder is 4.7db, which Peter Scheiber's 'high-separation' Tetrahedral Matrix did)

CBS SQ put all the separation in the Left/Right axis, in both the front and back channels - so when decoded with a non-logic decoder, Left or Right Back had infinite separation from the opposite back channel, while Left and Right Front had infinite separation between themselves too; but there was only -3db of separation between Left Front and Left Back/Right Back and Right Front and Right Back/Left Back and vise-versa (in SQ all crosstalk between channels was into the two opposing speakers, i.e. Lf into Lb & Rb) Center Front to Center Back had NO separation at all. As everyone on QQ probably well knows, decoded without logic, basic-matrix SQ sounds like the front and back channels are blended completely together - in other words, double stereo, which is basically what it was. So ElectroVoice was attempting to get compatibility with the most popular and widely licensed matrix system, SQ, while giving more of a front-to-back 'surround sound' effect when decoded.

BTW, QS's 'infinite' separation is between diagonals - so instead of infinite Lf-Rf separation as SQ has, QS has infinite Lf-Rb and Rf-Lb separation - the crosstalk from, say Left Front, is decoded into Right Front and Left Back with only -3db separation between them, so without Vario-Matrix, QS sounds almost like mono since it has basically no L/R separation - which makes it very, very difficult to keep the action of the Vario-Matrix below audibility - you can often hear the soundstage shift from left to right, or a CF vocalist pull to either side as a dominant sound comes in from the side. It's one of the reasons Sansui lets the Vario-Matrix pull mono vocals to the center of the room - to try and mask the side-to-side shifting.

For a GREAT introduction to matrixing, two good papers to start with, which should be available for everyone here to read shortly, I hope, are the July/August 1971 paper "Multichannel Matrix Systems Overview" by John Eargle and another of his papers from December 1972, "4-2-4 Matrix Systems: Standards, Practice & Interchangeability."

 

[Quadrockasaurus]

This arrived this morning for £59 delivered, about $95. It might be a few days before I can have a play with it:

Regards,

Peter

Far Out..!! Cheap and in great condition!!......If you can, let us all know what it sounds like...

cheers.

 

[Lucanu]

Not sure what "version" of the QS Decoder/Synth was included...but I've seen the QA-5000 alongside the QRX-7001 in a German Catalog on the web..(which I can't locate anymore), so it may be one of the late QS variations.

I've read on that catalog it has Type-A Vario-matrix circuit

Congrats, very nice unit Quadmusic!!