Technics SA-8500x

[gvl_guy]

Anyone know much about these Technics quads? I'm very interested in picking up one of them, but don't really know much about them (other than I assume rather weak matrix decoders.)

I'd love to know how reliable they are/were. Were there any particular problems they were known for? Are they pretty easy to get refurbished? I'm not one to be able to do it myself, but there is a decent shop near me that likely could do it if it's not too quirky/complicated.

Anything would be helpful.

(I've always loved these, at least in their look, and I think I might have a chance to pick up a used one.)

If not, can anyone recommend something to look for that won't totally break the bank? Thanks!

Thank you!!

 

[kfbkfb]

This Technics receiver has *automatic* front/back CD-4 separation (also uses the QSI-5022 CD-4 IC).

I've searched often for listening tests and measurements of this auto CD-4 separation system, haven't found any yet.

I'm very interested in how the auto F/B CD-4 separation system sounds (if CD-4 had started with this, it might have helped - no user adjustments would be needed, just play a CD-4 record [with a suitable turntable/cartridge/stylus]).


Kirk Bayne

 

[sjcorne]

I've got the standalone SH-400 demodulator unit (which I'd guess uses a lot of the same internal circuitry as the 8500x receiver?) and the "Hi-Blend" feature is a game-changer for CD-4 playback, it nulls most of the background noise without taking off too much high-end. It rescued some LPs I thought were pretty much unplayable due to high noise floor (Eagles - One Of These Nights, Carly Simon - Greatest Hits, etc).

 

[Doug G.]

I wouldn't hesitate if the price is reasonable. It is very beautiful. I also have an SH-400 and it only recently let me know the card edge connectors between the main and vertical daughter board need attention. It has otherwise been totally reliable. I mean, it's close to fifty years of age!

The SA-8500X also supports semi conductor (strain gauge) cartridges like almost all Technics/Panasonic quad equipment.

Doug

 

[geotex]

I have one that is currently on the bench for power supply issues and recapping. This unit came out late in the game, and had a lot of built-in features. One of the best was the auto-decoding of 4 channel sound. It works. It features built in decoders with automatic detectors, nothing else to add like many others. Also, a feature (?) I found is that it will create 4 channel audio from a stereo input. Mine looks just like the one in the ad posted here. My overall experience is limited with this unit, as I picked it up cheap when I was rebuilding Sansui Quads and stereos for an ebay store. I dug it out of the store room about 6 months ago, replaced a fuse to bring back the panel lights. A drop-dead beautiful unit with all the original type bulbs working. If you are thinking of doing self-repair on this unit, it is NOT an easy task as it uses individual boards tightly nested and interconnected with with old plugs and lots of soldered wires just long enough to prevent easy access to almost everything. Overall, this unit appears to be built with the same quality standards that made their turntables so popular.

 

[kfbkfb]

It features built in decoders with automatic detectors, nothing else to add like many others.

If possible, please use one of the CD-4 alignment discs and measure the front to back channel separation of the demodulator in the SA-8500x, I wish the SH-400 had switchable auto/manual f/b separation options.


Kirk Bayne

 

[Doug G.]

Fortunately, because of the meter, the separation adjustments on the SH-400 are very easy. No listening, wondering if you really heard where the back channel had the lowest output. Just look at the meter. Not that listening is all that difficult either, but...

The convention, back in the day, was to call the "decoding" element in matrix systems, a "decoder" and, in CD-4 systems, a "demodulator" to avoid confusion and we should continue to follow that convention. It's not like the "records"/"vinyls" controversy.

Doug

 

[kfbkfb]

AFAIK, Technics was the only company that developed an automatic front/back separation system, IMHO, had CD-4 caught on, complete auto adjustment (no carrier level or f/b separation) would have been a real plus.

I guess an SH-400 could be modified w/auto separation if the circuit diagram of the auto separation system can be found.


Kirk Bayne

 

[Doug G.]

It doesn't seem to be too hard to do. You just need a comparator-type circuit between the front/back channels and when the front channel receives a discreet signal, the back channel is set to minimum just like when you do it manually. Once set, it wouldn't have to be reset but there can be a monitoring circuit, just in case..

Doug

 

[kfbkfb]

https://www.hifiengine.com/manual_library/technics/sa-8500x.shtml
Technics SA-8500X service manual


Kirk Bayne

 

[DudeRocks]

Does anyone have any information on the logic board for SQ/RM on this? Is it the same one Panasonic used in the 949A? Seeing is this was their last big quad and they are under the same manufacturers Panasonic/Technics I would imagine that they would share similar components. Curious if it's full logic or wave matching logic, or did they for some odd reason go cheap with a half logic board from a few years earlier?

 

[kfbkfb]

IIRC, Panasonic/Technics didn't use any logic/separation enhancement system in the matrix decoders in their quad receivers (Panasonic [& JVC]) were big supporters of CD-4 (JVC invented CD-4).


Kirk Bayne

 

[DudeRocks]

IIRC, Panasonic/Technics didn't use any logic/separation enhancement system in the matrix decoders in their quad receivers (Panasonic [& JVC]) were big supporters of CD-4 (JVC invented CD-4).


Kirk Bayne

Right on CD4, but what was the version of logic that they used for the SQ/RM? The 949A I had previously seen somewhere that they upgraded the matrix decoder to a "full logic", with the 8500x being the last of their quad flagship I figure it would have been upgraded as well.

 

[kfbkfb]

I believe you're thinking of the Pioneer QX-949A (it did have an SQ matrix logic system, I don't know about a logic system for RM/QS):

https://www.quadraphonicquad.com/forums/threads/pioneer-qx-949a.32730/


Kirk Bayne

 

[DudeRocks]

I believe you're thinking of the Pioneer QX-949A (it did have an SQ matrix logic system, I don't know about a logic system for RM/QS):

https://www.quadraphonicquad.com/forums/threads/pioneer-qx-949a.32730/


Here's a pic of what I'm talking about about: the 1 (RM) and 2 sounds pretty good for SQ. What logic decoder are they using. I have a hunch it's going to be similar to the 949A but haven't found any mention of what it is exactly just yet. The search goes on.

Here's a pic of what I'm talking about about: the 1 (RM) and 2 sounds pretty good for SQ. What logic decoder are they using. I have a hunch it's going to be similar to the 949A but haven't found any mention of what it is exactly just yet. The search goes on.

 

[kfbkfb]

I never heard about a logic assisted matrix decoder being used in any Panasonic/Technics receiver.

The best option to resolve this issue is to look at a circuit diagram of the decoder circuits - I'd be really surprised if Panasonic/Technics receivers had more than basic (no logic) matrix decoders (SQ had several decoding options for no logic decoders: 10-10 blend, 10-40 blend for example).


Kirk Bayne

 

[gvl_guy]

Technics AKA Panasonic never used anything other than basic decoders for matrix in any of their quad receivers. The 949A was Pioneer....no relation...and was SQ Full Logic. The QX-949 (minus the A) was also basic decoding.

 

[Sonik Wiz]

Technics AKA Panasonic never used anything other than basic decoders for matrix in any of their quad receivers. The 949A was Pioneer....no relation...and was SQ Full Logic. The QX-949 (minus the A) was also basic decoding.

I must agree with you & @kfbkfb. The matrix decoding is simple with no logic assist of any kind. The documentation for the CD-4 is pretty good but not even a schematic for the matrix decoder section, just a PCB parts lay out. However even from this I can tell that neither of the matrix decode modes are for SQ. There's only 4 transistors for the whole matrix PCB & you can't do SQ with that. You need multiple phase shift elements that has a certain repeating parts layout that makes it easy to tell they are 90 deg phase shifters as needed for SQ.

So one of the decode positions probably matches RM and one will have different blend coefficients that might be closer to EV-4. Still, no SQ, no logic.

 

[kfbkfb]

aside:
The Panasonic/Technics automatic CD-4 Front/Back separaion circuit is diagrammed also.

I'll post a pin out of the QSI-5022 and perhaps the auto F/B separation circuit alone can be added to other (probably standalone) CD-4 demodulators, obviating the need for a CD-4 adjustment disc (except maybe for the carrier level adjustment).


Kirk Bayne

 

[kfbkfb]

https://www.worldradiohistory.com/A...0s/1974/Radio-Electronics-1974-06.pdf#page=39

Looks like QSI-5022 pin 25 is where the Front/Back separation adjustment is connected, I haven't done any circuit analysis for quite a while, maybe someone with circuit analysis software can isolate the automatic CD-4 Front/Back separation circuit in the SA-8500X.


Kirk Bayne