AMP: Sansui QA-7000 Quadraphonic Integrated Amp

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Quadrockasaurus

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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-7000 Quadraphonic Integrated Amp

Rarity: Rare
Average Sale Price: Unknown


Sansui QA-7000 Quad Integrated - Top-Front.jpg

Photo's are my unit....A pretty rare, and pretty cool Sansui Quad Amp. Love the Quad meters..!! It sounds somewhat like my QRX-6500 but a bit lighter in the bass, however my unit needs lots of work so don't take that assessment as gospel. My amp doesn't work out of the rear speakers, so I haven't spent too much time messing around with it. I think I've read this unit does not have the QRX style QS Synth decoders...it's the older "Single Band" ones...

Lots of Quad inputs available here including 3 Quad Aux In's & 2 Quad Tape loops...the Tuner input is also a Quad input. One unusual feature is the level set control which is like a second volume control...not sure what Sansui were thinking here :confused: as it's actually kind of annoying. I can't run it more than half way without maxing out the meters....

Another quirk is the 4 channel tape monitor switch...if you switch it to either of the "playback deck 1 or 2" positions, it prevents the "Rec Mode deck 2" switch from switching to the "Decoded Signal" position...locks that switch so you can't move it to there. Alternately, if you move the "Rec Mode Deck 2" to "Decoded Signal" position...it prevents the "Monitor" switch from moving into both the "playback deck 1 or 2" positions. So if your wondering why those switches won't move in certain situations...now you know, they are not jammed, that's how they work... :mad:@:

For such a flashy Quad unit it puts out a surprisingly low amount of power (15W x 4)...which might relegate this unit as a pretty curio in my collection, but with the pre-out connection available it could be used as a funky Quad pre-amp into a couple of more powerful stereo power amps...so there's a bit of flexibility there....:)

A cool looking unit with lots of switches & knobs to play with...


Sansui QA-7000 Quad Integrated - L - Front CLOSE.jpg

Sansui QA-7000 Quad Integrated - R - Front CLOSE.jpg

Sansui QA-7000 Quad Integrated - Meter CLOSE.jpg

Sansui QA-7000 Quad Integrated - Side R - Front.jpg

Some Basic QA-7000 Info:

Power Output: 15 Watts (8ohms) x 4 or 40 Watts (8 Ohms) x 2 ...via switch on back.
Weight: 30.0 Lbs.

Inputs/Connections Available:
Phono Inputs x 2
Quad Aux In x 3
Quad Tape Loop In/Out x 2
Stereo Tape Loop In/Out x 1

Quad Pre Out
Quad Main In
 
Last edited:

rustyandi

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I had one of these years ago
A friend has it now
last time I spoke to him it had a fault in it
The QS decoder was Vario Matrix a single band early version
like the QSD2
Not as good as QSD1 or the new Decoder
 

Quadrockasaurus

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I had one of these years ago
A friend has it now
last time I spoke to him it had a fault in it
The QS decoder was Vario Matrix a single band early version
like the QSD2
Not as good as QSD1 or the new Decoder

Yep...I've been messing around with it, and even though the rear speakers don't work, both front & rear headphones work so the pre-amp is probably fine. Using the Phones alternately in the QS Synth mode...I didn't hear any "Vario-matrix-ing" going on so I suspected the earlier "Single Band" decoder as well....a bit of a bummer.
 

Wagonmaster_91

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These really are beautiful amps. As you say, because of their low power output, it is best to pair it with a couple of stereo power amps and use it as a very flexible quad preamp.

The Level control is actually an input gain control, the same as you find on most professional mixers. This allows you to adjust the level of the various input components (tape deck, tuner, etc.) to allow you to give proper headroom for that input. For example, let's say you have a quad 8-track player in the Aux 1 that has a hotter (louder) input level than your the tuner you have plugged into the Tuner input. The Level control allows you to turn down the signal coming from the 8-track player so that the incoming signal doesn't overload the preamp (the maxing out of the meters you mention) or bring up the level of the Tuner input signal so that the amp is operating in its optimal range for lowest distortion and minimize the "noise" you might be amplifying with a signal that is too low. As I stated, this is a feature you find on any good multi-channel mixer because microphones vary widely in output from type to type and model to model and a gain control on each input allows you to balance all the levels more easily. An input gain control really isn't needed for a modern home sound system preamp as most components today (CD players, DVD players, etc.) have pretty standard output levels. Few home amps had this feature after the late 70's.

The reason for the lock-out feature on the 4 channel tape deck switches is because it is assumed that if you are listening to a quad tape deck, the four channels are discrete and you would not want the rear channels to be decoded or derived from the front channel signals. For example, let's say your quad recording has a trumpet in the front left, guitar in the front right, bass in the rear left and drums in the rear right. If you could engage the "Decoded Signal" switch, the signals fed to rear channels would be derived (decoded or synthesized) from the trumpet and guitar channels. You would not hear the bass and drums channels. If you were dubbing from one quad deck to another quad deck, the lock-outs protect you from accidentally recording the "wrong" rear channel signals. In the early days of quad, working with the differences between discrete quad sources and quad decoded from two channel matrices (SQ,QS, etc.) could get very confusing for consumers, so the lock-out switches on the QA-7000 are an example of Sansui trying to make things a little easier to get right.

If you were playing a reel-to-reel dub of an SQ encoded LP, Sansui assumes you would be playing that on a 2 channel deck plugged into one of the stereo inputs and that signal is allowed to have "Decoded Signal" engaged and create the signals needed for the rear channels.

Great pics, too. Thanks for this.
 

par4ken

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I picked up one of these earlier this year and love this single band decoder for stereo enhancement, I also own a QSD-1 and that unit definitely colours the sound. The QA-7000 is very transparent and provides an amazing and smooth enhancement of most stereo, I haven't been using the built in amplifier (most 70's vintage amps weren't that great sounding anyway), I'm just using it as as preamp/decoder. The Phase Matrix decoding of SQ isn't all that great but is better than the decoding of many/most other receiver/amp built in decoders! The best feature of this amp is it has four discrete inputs, tuner (anticipating Quad FM), Aux 1 and 2 and Tape monitor!

I think the triple band decoder (QSD-1) was what seemed like a good idea at the time but wasn't all that great in practice (I know that others disagree with me). Sansui's final high end decoder the QSD-1000 reverted back to single band operation, for good reason I think.

These are well worth the usual asking price of about $400, I would even pay more. I think that someone got one for a bit more than $100 recently on eBay a real steal!
 

par4ken

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I did a search of the Vario-Matrix boards F-2048 and F-2047 and found that they were used in the QRX-5500 as well. My QA-7000 manual showed them as blocks only, no parts list or schematic, the schematic can be found in the QRX-5500 service manual. They use discrete components rather than the HA series IC's, dispute being an early Vario-Matrix decoder it preforms very well indeed. An added benefit is that without any specialized parts it should be possible to keep them running indefinitely!
 

surround.sound.enthusiast

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This is the only model (along with the Sansui QSC-9050, apparent Japan-only equivalent) that I've ever seen "Surround" and "Hall" setting for both QS decoding and QS synthesizing. To this point I've only ever seen "Surround" and "Hall" settings for synthesizing only, but I'm also not very familiar with Sansui receivers.

So, for anyone who's owned this model, do you notice much or any difference in the two settings when decoding QS material?
 

Quad Linda

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A year or so ago, a GF of mine gifted me a Sansui QRX-5500 receiver her late Father bought. I use it for synthesizing and QS decoding on my main system, which also has RM decoding on a Sony SQD-2020. Modern B&K 7.1 Preamp and Power Amps run the system itself. The QRX-5500 and many of it's brothers and sisters have Surround and Hall modes for both QS Decoding and Synthesizing. Their knob configuration is identical. It also has a 1/4 turn direction knob.

sansui-qrx-5500.jpg
 

par4ken

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I've recently done some servicing on my QA-7000. The front channels had become nothing but static, I found that the transistors on the B.T.L. board had become leaky, so I just bypassed that board for now, it's only purpose is to allow you to bridge the amp for stereo (what a waste). I did some re-capping as well, replacing with film types wherever practicable.
I originally thought that the difference between QS, Regular Matrix (Hall and Surround) and QS Synthesize (Hall and Surround) was that the all pass phase shifters were switched out in the Synthesize mode, but I found that not to be the case. QS Regular Matrix Surround is just normal QS, Hall focuses a bit more sound to the front. QS Synthesize, Hall and Surround are the normal Hall and Surround modes. Originally the decoder in my amp sounded good but seemed to image between the speakers, indicating less than perfect separation. I tried adjusting the pots by trial and error. I figured out an easy procedure, with the meters on the front of the amp you just need a test signal. Adobe Audition working through your sound card is excellent for this. Attached is my procedure, I provide it with no guarantee that it's totally correct, but it worked fine for me, you don't have to be a tech to accomplish it. Checking different schematics I found that in the QRX-5500A and QRX-7500A the F-2047 decoder board is replaced by the F-2084 which uses the the Hitachi QS phase discriminator chips, the same as all the latter units. The F-2048 board is common to both.
 

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jagoeman

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Very nice procedure!

The Sansui QRX-3500 behaves somewhat different. Below the same procedure wit some minor adjustments:

Set all tone and balance knobs in mid position. Loudness and filters in off position.

Use Vrms meters or a scope to monitor LF(27), RF(25), LR(07), RR(03) of board F-2048 or pick up the signals in a later stage. On the QRX-3500 this can easily be done on the remote control socket: pin 1 = LF ; pin 3 = RF ; pin 5 =LB; pin 7 = RB.

On F-2047 are a row of pots. Looking from the front of the amp, from left to right: VR05, VR03, VR01, VR02, VR04 and VR06.

Connect a 1kHz, 300 mV in phase tone to 2-CH TAPE REC L and a second 1kHz out of phase tone to 2-CH TAPE REC R. You need a 0° or 180° out of phase tone for front/rear and 90° and/or 270° degrees for SQ testing.

Set the function knob to QS (QS Surround) mode.

Feed the 180° out of phase tone to decoder, adjust VR05 for minimum on the front / maximum on the rear.

Feed only a left signal in and adjust VR01 for minimum on the right and maximum on the left.

Feed a only a right signal in and adjust VR02 for minimum on the left and maximum on the right.

Front and rear levels should now be equal in both cases.

Set the function knob to Hall mode.

Feed in an 180° out of phase signal and adjust VR03 for maximum in the rear and minimum in front.

Set the function knob to Phase Matrix mode.

Feed in an in phase signal and adjust VR04 for minimum in the rear and maximum in front.

Then adjust VR06 for minimum in the rear and maximum in front.

For SQ testing: applying a phase shift of 90°will simulate an SQ signal with maximized LB signal and minimized RB signal. Appling a phase shift of 270° will do the opposite.

It is not quite clear how to optimize the lower pots VR07 and VR08. Kept the original +/- mid position.

The decoder works great now!

Does anyone have an idea on VR07 and VR08?
Two testpoints TP1 and TP2 seem to be involved when looking at the schematics.
 
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