RCVR: SONY SQR-6650

[VFET4ever]

SONY SQR-6650 QUADRAPHONIC RECEIVER

Rarity: Uncommon

Average sale price: Varies - from $75 to $100 depending upon quality and seller

Year of introduction: 1974

Well, I paid €65 (~$90) for it... and saw only one other unit for sale last year for around the same price. I would like to know what kind of prices have been observed by others, and if it is put up for sale (more) regularly or not.

The aluminum faceplate is grey-bronze, giving it a very distinct look normally reserved for Sony’s upper-end gear (several years later), and quite different from the STR receiver series from the same era which have regular brushed aluminum faceplate with aluminum knobs. The photos don’t show it well, but the position of the four VU-meters behind double windows gives it a very deep perspective look, quite awesome in reality. It is clear that the marketing department wanted ‘good looks’.







Before going inside, first some back-side pictures. Besides the regular stereo sources, an external decoded quadraphonic input can be connected directly to the output amplifier stage, bypassing the internal SQ decoder when the ‘system’ selector switch is put on ‘4-ch’. Fortunately they did put this direct 4-channel input on it, you will see why later…

The black grill is a bit optimistic; the power output of this receiver won’t make cheese to melt. In fact, it is holding the complete heatsink/OPS PCB assembly in place; the assembly can be easily pulled out of the chassis for service.





As explained in more detail later, there is one special ‘Hi-Power 2-Ch Speaker Output’ terminal, activated by the little black switch when put on ‘2CH’. It is red colored with a caution label for a good reason: the terminals are floating from the chassis; shorting the terminals with the chassis or the terminals above can (will) fry some amplifier components.



And the specs before opening the bonnet.

 

[VFET4ever]

Ok, bonnet open…. The unit is rather well stuffed, there are two other boards (tone control and SQ decoder) on the other side, as showed later.



The tuner is straight forward, full solid state, nothing particular bad or spectacular to report, the reception is reasonable accurate and warm sounding. Despite its age with all original components, there is whatsoever no noise or other distortion audible once a channel is picked up, not even when in stereo. Stereo separation is very good



And a general view of the bottom, the SQ decoder board the middle. More detailed views later.

 

[VFET4ever]

The output amplifier is a full discrete amplifier section, rated 4x 8W or 2x 25W. Actually, difficult to define reading the above output power specs… I wonder if the claimed power at 4 ohm can actually be developed by this circuitry.

Anyway, it seems that this SQR model is the only one amongst the SQR series which has a discrete amplifier section. The service manuals of the other models show thick-chip power amp modules (SQR-4750 = 4x STK-056A, SQR-6750 / 8750= 4x BX-249A). It seems the x750 series is a different series all together, but the trade-off is that this model has no real SQ decoder ICs (see later).

The amp board can be easily removed by pulling it out backwards (after unscrewing the grill); all cables are connected using pins, though no cable is labeled. Pics and notes are mandatory before service.



Where the circuitry of this unit is also special, is the quite unique ‘Hi-Power 2-Ch Output’. In case the little slide button on the back is set to 2 channel mode, then the output of front power amp is fed into the input of the rear power amp, via an attenuating resistor (which levels the output back to input signal level). As the output is inherently in the opposite phase of the input, the rear output amplifier amplifies in the opposite phase. Now, connecting the speaker between the live terminals of the front and rear power amplifier, this means doubling the power. This is why the red-colored 2 channel speaker terminals at the back are ‘floating’ from the chassis, and shouldn’t be shorted (there is whatsoever no protection circuit in this unit). Note that the x750 series have the same 2/4 channel switch an output power doubling, but they just put the front and rear power amplifier in parallel.

Note the absence of emitter resistors in the output stage, only a diode to provide some balancing. The output devices (2SC1060) are from Sony, and are actually used in many low-power Sony units of that era. A knowledgeable friend of me said that they cannot be easily replaced, as the circuit topology depends on their characteristic (and of the diode in the middle). Hmm. The remaining circuit is quite Sony standard for that era, of course limited by space constraints.

One particular downside: this unit has only ‘front’ headphone connector, while the entire x750 series has front and rear headphone connectors. Big shame; a real missed opportunity.

 

[VFET4ever]

The SQ decoder is… not a real SQ decoder…. Is more an angle shifting and channel mixing design. Before showing the board, reading Sony’s explanation is required. As mentioned before, fortunately they did provide a 4 channel input.

A sort of hidden engineering humor: "SQR-6650 uses simplified SQ decoder which does not contain logic circuit as shown if Fig. 1-2" Yeah that makes sense…





Which translates in this circuitry:



The SQ decoder board is located under the power amp board, using less regular axial lead capacitors, of course due to the space constraints.



The tone control and selector switch section is well-build, full quad set-up.

 

[VFET4ever]

Remains the power supply section. A bit too compact, they could have made a larger board for this. The small black-colored heatsink gets pretty warm, heating up the capacitors around it, notably the one above it. Room for (future) improvement.



The power main power supply caps are accessible from the bottom, like the mains voltage selector swich.



The main power supply caps are not large, not in capacity (for 21st century), not in dimension. It will be a challenge to find such small-sized caps with solder lugs for future recap, regardless of the capacity which can be easily increased maintaining the same dimensions.



So, how does it sound? Well, a recap is in order despite all components are in (very) good shape. The lower end is too warm/blurry, the higher end is missing sharpness and detail, i.e. old caps. I noted that all power supply caps get too warm, even with the bonnet open. A sign of aging.

Talking about bonnet open or closed, the large amount of light bulbs creates a lot of heat inside the unit, too much. Perhaps an issue to take care of during future rebuild (anybody any modern solutions, such as LEDs, but maintaining same coloring ?)

Another little bug is that the ‘tuner-in’ meter (which in fact is rather a tuner out meter) is stuck in max position, and 1 or 2 VU-meters can stay stuck for a few seconds. Knowing Sony, these must be standardized components and I spotted similar meters in various tuners and stereo receivers from the same era. Applying a reverse voltage (with limited current!) might unlock the tuner meter. Lubrication seems impossible.

The issue being, how much investment is justified in such a unit? Ok, it’s passion, so forget about breaking even, but still…

Enjoy,
Ozzy

 

[Disclord]

I surprised that it's a no-separation basic SQ Matrix design - especially since it's a 1974 model. It's such a shame too because Sony worked on and patented advanced crosstalk cancellation decoders for both SQ and QS and even had IC designs for them. But all they ever released were gain-riding logic and gain-riding w/Vari-blend Logic SQ decoders.

 

[VFET4ever]

Yes, indeed. Specially if you know that all other SQR modles have SQ decoding ICs in them.

 

[Quad Linda]

This is a beautiful piece. Very clean lines and the controls are easily understandable. All that being said, we were a large Sony dealer. We sold piles of Sony stereo receivers and compacts, but didn't stock any of the Quad receivers. We stuck with Marantz, Pioneer and JVC Quad receivers.

I wonder what they were thinking when they designed these. This model doesn't even have a Quad tape loop. Still, it is gorgeous.

Linda

Yes, indeed. Specially if you know that all other SQR modles have SQ decoding ICs in them.

 

[Disclord]

This is a beautiful piece. Very clean lines and the controls are easily understandable. All that being said, we were a large Sony dealer. We sold piles of Sony stereo receivers and compacts, but didn't stock any of the Quad receivers. We stuck with Marantz, Pioneer and JVC Quad receivers.

I wonder what they were thinking when they designed these. This model doesn't even have a Quad tape loop. Still, it is gorgeous.

Linda

Linda, was SuperScope kept separate from Sony quad dealers at the time? Or was it still Sony SuperScope? I ask because I've never known if SuperScope ever handled any Sony quad equipment or if the connection between companies was pretty much over by then?

 

[Quad Linda]

Superscope distributed Sony tape recorders in the US, starting in 1957. Their original "product" was widescreen movie technology, hence the name. Superscope distributed Sony Quad reel-to-reel and Q8 decks. "Superscope continued to market and distribute Sony tape recorders exclusively in the United States until January 1, 1975, when Sony acquired back distribution rights to its line of tape recorders from Superscope."-from Superscope's website. for more history on Marantz/Superscope: http://www.superscopetechnologies.com/t-about.aspx I remember the Marantz/Superscope people mentioning the expiration of their distribution agreement as early as '73. There were no Marantz tape decks until '74-'75.

Until 1975, Sony Corp. only marketed tv's, receivers, compact systems, car fi (cassette only) and portables. We sold them all, though I don't remember Sony turtables until the late '70's. I still own a Sony PSX-6 turntable. We sold a few Superscope portables.

We were so fortunate that all the big players in hifi had regional distribution centers within 10 miles of our store. We had a tighter connection to the companies than I ever had in other locations. For a wide-eyed kid who was an audiophile, this was nirvana. My first hi-fi gig was assistant manager in a killer store.

I never had direct experience with Sony Quad receivers. Sony & Marantz were our best-selling stereo receivers. I owned a Sony STR-7065A stereo receiver from '74-'83. 85 w/ch RMS. Great power for it's day. Powerful amp, lots of features, great tuner and a logical control layout. I'd expect that SQR-6650 has a good tuner, as well. My cousin still has my STR-7065A. After 6 months, my STR-7065A became Quad, with the addition of a Marantz 2440, SQA-1 and a JVC-4DD5. I still own the other equipment. STR-7065A info, specs and pix: http://www.classic-audio.com/sony-str7065-p-276.html One of the best pieces I ever owned.

It's a shame that Sony didn't use a better SQ decoder in their Quad receivers. Can you imagine if they had a killer decoder, ala Lafayette LR-4000? We'd be drooling today over the Sony SQRS-9900, as we do over Marantz 4400 and QRX-9001. The second S stands for the built-in oscilloscope. 100 w/ch x 5, a killer tuner and full-logic wavematching. Cooler than any Lirpa gear. We can dream of what never was.

Linda
Lingering on Quad Memory Lane.

Linda, was SuperScope kept separate from Sony quad dealers at the time? Or was it still Sony SuperScope? I ask because I've never known if SuperScope ever handled any Sony quad equipment or if the connection between companies was pretty much over by then?

 

[Disclord]

Superscope distributed Sony tape recorders in the US, starting in 1957. Their original "product" was widescreen movie technology, hence the name. Superscope distributed Sony Quad reel-to-reel and Q8 decks. "Superscope continued to market and distribute Sony tape recorders exclusively in the United States until January 1, 1975, when Sony acquired back distribution rights to its line of tape recorders from Superscope."-from Superscope's website. for more history on Marantz/Superscope: http://www.superscopetechnologies.com/t-about.aspx I remember the Marantz/Superscope people mentioning the expiration of their distribution agreement as early as '73. There were no Marantz tape decks until '74-'75.

Until 1975, Sony Corp. only marketed tv's, receivers, compact systems, car fi (cassette only) and portables. We sold them all, though I don't remember Sony turtables until the late '70's. I still own a Sony PSX-6 turntable. We sold a few Superscope portables.

We were so fortunate that all the big players in hifi had regional distribution centers within 10 miles of our store. We had a tighter connection to the companies than I ever had in other locations. For a wide-eyed kid who was an audiophile, this was nirvana. My first hi-fi gig was assistant manager in a killer store.

I never had direct experience with Sony Quad receivers. Sony & Marantz were our best-selling stereo receivers. I owned a Sony STR-7065A stereo receiver from '74-'83. 85 w/ch RMS. Great power for it's day. Powerful amp, lots of features, great tuner and a logical control layout. I'd expect that SQR-6650 has a good tuner, as well. My cousin still has my STR-7065A. After 6 months, my STR-7065A became Quad, with the addition of a Marantz 2440, SQA-1 and a JVC-4DD5. I still own the other equipment. STR-7065A info, specs and pix: http://www.classic-audio.com/sony-str7065-p-276.html One of the best pieces I ever owned.

It's a shame that Sony didn't use a better SQ decoder in their Quad receivers. Can you imagine if they had a killer decoder, ala Lafayette LR-4000? We'd be drooling today over the Sony SQRS-9900, as we do over Marantz 4400 and QRX-9001. The second S stands for the built-in oscilloscope. 100 w/ch x 5, a killer tuner and full-logic wavematching. Cooler than any Lirpa gear. We can dream of what never was.

Linda
Lingering on Quad Memory Lane.

The SuperScope widescreen movie process is still alive today, although it's now known as "Super 35" and had a bad rep until James Cameron proved that good results could be obtained with True Lies, The Abyss, Titanic, etc...

I never knew that SuperScope was limited to Sony's tape gear - I don't know why, but I thought they handled all of Sony's equipment until Sony took over in the 70's. You learned me something new today.

One thing I miss about the Sony of the 70's and early 80's as compared to the Sony of today is the customer support - Sony always worked to make sure a customer was satisfied and happy with their product when a problem cropped up. Heck, when they abandoned the one-hour Beta X1 speed for Beta II speed, owners of the first stand alone Betamax and the Betamax/TV combo were given the Betastack tape changer for free. Sony's a mess of a company now - like RCA was in the 70's and goes from one new product business to another.

I'll never understand why Sony didn't introduce an advanced SQ or QS decoder - Until the Tate in 1979, Wave-Matching Logic w/Vari-Blend was as advanced as SQ Logic decoding got on the consumer market - well, except for the Scheiber Sonics 360 Spatial Decoder, but it was so expensive, well over $1,500, that it couldn't have made a dent in the market (and didn't). While Audionics was working on Shadow-Vector and CBS was dropping Paramatrix IC development to back the Tate DES IC design, Sony could have swooped in with their advanced crosstalk cancellation decoder at a reasonable price and had the market to themselves.

It's always fun to think "What if?"

For those who've heard Sony's Full Logic SQ decoders with Vari-blend, how do they perform as compared to the Lafayette SQ-W? While Lafayette used a discrete circuit of their own design that both performed well and sounded good, Sony had the Full Logic + Vari-blend down to an IC set that had much better sound quality, from what I've been told, than the Motorola SQ Full Logic IC's, which were not very high in the Fi.

Sony's specs on the SQ decoder in the receiver of this thread are awful - only 14db L/R separation IN FRONT??? That's a rather narrow soundstage because you need 20db minimum of L/R separation in front to localize a sound clearly at a single speaker. Reduced separation Front to Back and L/R in back is much less critical. I don't know of any other non-logic decoder that used a 20/40 blend - they were all 10/40 which was CBS recommendation for non-logic SQ, or 10/20 if they had Full Logic.

 

[Quad Linda]

I was very high on Sony back in the day. I bought a 12" Sony color TV in '70. It bit the dust in '98! Fantastic picture and build quality. My Panasonic Plasma is the first TV I've owned with a better picture.

I soured on Sony in '79 when I bought their new 3-head cassette that did metal tape. It was a lemon, and I got no satisfaction from the Sony rep, even though we were the largest Sony dealer in the country. It ended my love affair with Sony. I never bothered with a replacement and ultimately replaced it with a Kenwood KX-1030, 3-head, metal and a test tone generator for tweaking record bias. One of the best pieces I've owned. A friend of mine still has it. Since then, I owned a Sony VHS, another lemon. I am pleased with my Sony SACD & Blu-Ray players.

Linda

The SuperScope widescreen movie process is still alive today, although it's now known as "Super 35" and had a bad rep until James Cameron proved that good results could be obtained with True Lies, The Abyss, Titanic, etc...

I never knew that SuperScope was limited to Sony's tape gear - I don't know why, but I thought they handled all of Sony's equipment until Sony took over in the 70's. You learned me something new today.

One thing I miss about the Sony of the 70's and early 80's as compared to the Sony of today is the customer support - Sony always worked to make sure a customer was satisfied and happy with their product when a problem cropped up. Heck, when they abandoned the one-hour Beta X1 speed for Beta II speed, owners of the first stand alone Betamax and the Betamax/TV combo were given the Betastack tape changer for free. Sony's a mess of a company now - like RCA was in the 70's and goes from one new product business to another.

I'll never understand why Sony didn't introduce an advanced SQ or QS decoder - Until the Tate in 1979, Wave-Matching Logic w/Vari-Blend was as advanced as SQ Logic decoding got on the consumer market - well, except for the Scheiber Sonics 360 Spatial Decoder, but it was so expensive, well over $1,500, that it couldn't have made a dent in the market (and didn't). While Audionics was working on Shadow-Vector and CBS was dropping Paramatrix IC development to back the Tate DES IC design, Sony could have swooped in with their advanced crosstalk cancellation decoder at a reasonable price and had the market to themselves.

It's always fun to think "What if?"

For those who've heard Sony's Full Logic SQ decoders with Vari-blend, how do they perform as compared to the Lafayette SQ-W? While Lafayette used a discrete circuit of their own design that both performed well and sounded good, Sony had the Full Logic + Vari-blend down to an IC set that had much better sound quality, from what I've been told, than the Motorola SQ Full Logic IC's, which were not very high in the Fi.

Sony's specs on the SQ decoder in the receiver of this thread are awful - only 14db L/R separation IN FRONT??? That's a rather narrow soundstage because you need 20db minimum of L/R separation in front to localize a sound clearly at a single speaker. Reduced separation Front to Back and L/R in back is much less critical. I don't know of any other non-logic decoder that used a 20/40 blend - they were all 10/40 which was CBS recommendation for non-logic SQ, or 10/20 if they had Full Logic.

 

[Disclord]

I was very high on Sony back in the day. I bought a 12" Sony color TV in '70. It bit the dust in '98! Fantastic picture and build quality. My Panasonic Plasma is the first TV I've owned with a better picture.

I soured on Sony in '79 when I bought their new 3-head cassette that did metal tape. It was a lemon, and I got no satisfaction from the Sony rep, even though we were the largest Sony dealer in the country. It ended my love affair with Sony. I never bothered with a replacement and ultimately replaced it with a Kenwood KX-1030, 3-head, metal and a test tone generator for tweaking record bias. One of the best pieces I've owned. A friend of mine still has it. Since then, I owned a Sony VHS, another lemon. I am pleased with my Sony SACD & Blu-Ray players.

Linda

My favorite company was always Pioneer due to their LaserDisc players and discs - and the way they doggedly stuck with the format. The one TV I always wanted, but my parents would never buy, was a Mitsubishi one-piece front projector - the kind with the pull out mirror. Mitsubishi's front projectors not only had a better picture than any other projection set on the market, but the cabinetry of the projector was awesome - it had folding doors to cover the screen and when all closed up, it looked like a hutch or china cabinet, not a projection TV. The Pioneer projector we sold at Video Etcetera for $2,200 couldn't even compare to the Mitsubishi's picture quality. In the mid 90's I bought a Mitsubishi rear-projector - it was a total lemon - they ended up replacing it with a new model and that one only lasted about 2 years before it bit the dust too. I've never bought another Mitsubishi product after that.

A company that is really changed - so much so that it's now only a 'name' for cheap products is Fisher. It's hard to believe, looking at them now, that they were a real company at one time, with their own R&D, etc. Of course, it's the same for RCA, Magnavox, Sansui... At least Marantz has managed to hang in there, despite going through different owners over the years.

 

[Quad Linda]

Mixed bag with me and Pioneer. I sold their Elite, the best mass-produced projection and plasma TV's. Sorry they exited that business. I had a PLA-35 turntable until '83. I loved it. My cousin still has it. I bought a Pioneer DVD in '99. It died 4 years later.

I've had good luck with Marantz. My 2440 still works very well.

It's sad that Sony has not maintained their build quality, but who has? Very few mass-produced electronics have the build quality they did when Quad was "in vogue."

Linda

My favorite company was always Pioneer due to their LaserDisc players and discs - and the way they doggedly stuck with the format. The one TV I always wanted, but my parents would never buy, was a Mitsubishi one-piece front projector - the kind with the pull out mirror. Mitsubishi's front projectors not only had a better picture than any other projection set on the market, but the cabinetry of the projector was awesome - it had folding doors to cover the screen and when all closed up, it looked like a hutch or china cabinet, not a projection TV. The Pioneer projector we sold at Video Etcetera for $2,200 couldn't even compare to the Mitsubishi's picture quality. In the mid 90's I bought a Mitsubishi rear-projector - it was a total lemon - they ended up replacing it with a new model and that one only lasted about 2 years before it bit the dust too. I've never bought another Mitsubishi product after that.

A company that is really changed - so much so that it's now only a 'name' for cheap products is Fisher. It's hard to believe, looking at them now, that they were a real company at one time, with their own R&D, etc. Of course, it's the same for RCA, Magnavox, Sansui... At least Marantz has managed to hang in there, despite going through different owners over the years.

 

[Disclord]

Mixed bag with me and Pioneer. I sold their Elite, the best mass-produced projection and plasma TV's. Sorry they exited that business. I had a PLA-35 turntable until '83. I loved it. My cousin still has it. I bought a Pioneer DVD in '99. It died 4 years later.

I've had good luck with Marantz. My 2440 still works very well.

It's sad that Sony has not maintained their build quality, but who has? Very few mass-produced electronics have the build quality they did when Quad was "in vogue."

Linda

Pioneer really changed the home video world when they introduced their Elite 40-inch rear projection set in 1987 or so, and later the 45 and 50 inch versions. For the first time a projection TV had the resolution and brightness of the best CRT-based TV. It was a massive R&D project for them and it really paid off - and every other company in the rear projection business had to scramble to catch up - much to the benefit of consumers.

Pioneer was always frustrating though with US LaserDisc though because they produced players for the Japanese market that had performance and build quality that couldn't be matched by anything they produced for sale in the US. Their Elite model LD players here were 'regular' players in Japan and not considered anything special. And they refused all requests by US LD consumers to sell the players like the HLD-X1 and LD-S9 here - both players had super-fine red lasers, like the first top-loading players, so they could track even the worst discs, and they had sophisticated picture processing, 3D motion adaptive comb filters, etc... and were built to battle-tank standards - the HLD-X1 (which also played high-definition MUSE LD's) weighed 60+ pounds. And NONE were CD/LD players - they were LD only and meant to be the very best. But we weren't allowed to have them here. Same with VCR's - JVC and others sold Super VHS VCR's in Japan that recorded 16-bit PCM stereo along with the video, in addition to the standard Hi-Fi tracks. And stand-alone recordable Blu-ray units have replaced the VCR in Japan as a home recording format for digital Hi-Vision broadcasts - but again, we aren't allowed to have them here. In fact, if you want to record and keep a show on TV now, there's no easy way to do it in HD like when VCR's were the main format for recording NTSC - JVC's W-VHS format, that was designed as a consumer format for recording any 1125-line HD format via component inputs, was sold only through pro-channels here - and with a considerable price hike and most of the features removed. It's all so frustrating.

And yes, build quality is nothing like it was - product longevity is not something companies strive for now.

 

[VFET4ever]

Until 1975, Sony Corp. only marketed tv's, receivers, compact systems, car fi (cassette only) and portables.

.....

It's a shame that Sony didn't use a better SQ decoder in their Quad receivers. Can you imagine if they had a killer decoder, ala Lafayette LR-4000? We'd be drooling today over the Sony SQRS-9900, as we do over Marantz 4400 and QRX-9001. The second S stands for the built-in oscilloscope. 100 w/ch x 5, a killer tuner and full-logic wavematching. Cooler than any Lirpa gear. We can dream of what never was.

Hi Linda,

Thanks for your exhaustive input.

I can't tell for the USA, but Sony was by far world's largest audio-video manufacturer throughout the 70 and 80's. (refer to TVK Sony/Sony Vaults). Many folks also don't know that Sony is really the leading company in the professional video and television world; walk into any television or radio studio and it's Sony what's out there for the last 4 decades. Unfortunately, most folks know Sony from their massive procuded portable audio and some mid-end hifi, creating a mid-stream image for the big public. Big mistake concerning 70's Sony gear ! Perhaps that Sony wasn't that present early 70's in the USA for hifi audio, they sure were in Europe and Asia. The european vintage hifi market is flooded with Sony's , your precious STR-7065A comes up for sale a few times a month

Another unknown (and heavily underrated) fact is that Sony had significant semiconductor R&D and manufacturing; VFETs being only one of the mythical high-end products they came up with. Unfortunately, the new CEO early 80's, decided to pull the plug out of their own semiconductor branch, destroying 20 years of excellence (well, the whole hifi business went plastic in the 80's), and introducing the mass-produced mobile stuff.

Their hifi audio branch started in the 50's and becoming strong througout the 60's, leading the hifi industry in the 70's. Now, the pictured SQR-6650 receiver is actually lower-end stuff for Sony, compared with all the other 70's Sony stuff I have/had. Sure, other brands had (much more) impressive receivers, sometimes a better R2R deck, but their catalog was thin compared to Sony. The Sony TA-8250 proving their excellence early 70's, for example.

Ok, back to the thread topic, the 'other' SQR decoders actually are equipped with decent SQ decoder chips. I have the service manuals of:
- SQR-4750
- SQR-6650
- SQR-6750
- SQR-8750
and compared them. First thing to say: the x750 models are similar in design, the pictured 6650 is a stand-alone loner.

In fact, the 6750 and 8750 are identical (exactly the same circuitry for SQ decoder, tone, power amp stage, etc); the 8750 only puts out more power due to higher rail voltages (...no comment...). This is interesting to know ! The 8750 is sold expensive being the top of the line, while the 6750 can be had for half the price.

The 4750 has almost identical SQ decoding section, so let's compare and find the 7 differences

This is the SQ decoding section of the SQR-4750:



And this is the SQ decoding section of the SQR-6750 and 8750:



Almost identical....

Hence, the x750 series are definitely nice SQ receivers to acquire ! In which case I would recommend the 6750 model.

In fact, I wouldn't mind to let the above-pictured 6650 unit go. Anybody interested? (located in France).

cheers,
ozzy

 

[Disclord]

I have the schematic to the Sony SQD-2010 stand-alone decoder and it looks almost identical to the receivers full-logic SQ sections you posted. It appears that Sony found a good design and, for the most part, stuck with it.

Sony's Full Logic decoders, in discrete circuit or IC form, were all fast in their logic attack times, which helped to hide side-effects of the gain-riding process, and is something that couldn't be said for most other full-logic SQ decoders, including CBS' own professional version. In the Consumer Reports large-scale test of quad receivers, only the Lafayette and Fisher receivers Full Logic SQ decoders got good marks for their SQ decoding - most others were rated poorly - some, like the Kenwood, failed badly, with very audible decoding artifacts. Strangely, CR didn't test any Sony receivers.

 

[VFET4ever]

The problem I have with consumer tests is the fake sense of 'unbiased reviews'. If a particular brand can jeopardise the positive outcome of some other(s), then, well, forget to test that particular brand....

Anyway, so it seems there are a couple of interesting SQ decoders with build-in tuner ?

 

[djim]

Ok, bonnet open…. The unit is rather well stuffed, there are two other boards (tone control and SQ decoder) on the other side, as showed later.

View attachment 4267

The tuner is straight forward, full solid state, nothing particular bad or spectacular to report, the reception is reasonable accurate and warm sounding. Despite its age with all original components, there is whatsoever no noise or other distortion audible once a channel is picked up, not even when in stereo. Stereo separation is very good

View attachment 4268

And a general view of the bottom, the SQ decoder board the middle. More detailed views later.

View attachment 4269

I have the same system, but it appears to have kaput power transformer. Can you (anyone) post the Secondary voltages for that? Transformer secondary has pair of blue (for lamps), pair of red to power board, and a single violet wire, also to the power board. Voltages coming off the power board (and to the amplifier board according to block diagram) are +24, -17, and +15v.