1976 Popular Electronics Construction Project
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HI TopTip
Not sure why you would call this a half logic decoder. "Logic" designated decoders we're the province of CBS/SQ. Sansui had Type A or Type B. This design is Type A with F/B and L/R sound discrimination. It is very similar to the Sansui QSD-2.
I purchased & built two of these designs from Bob Coleman at Photolume many years ago. Find the whole article here:
http://www.americanradiohistory.com/Archive-Poptronics/70s/1976/Poptronics-1976-12.pdf
I added a 200Hz Xover 6dB and made a 2 band decoder. The function switch was a nightmare to wire. But as much to my surprise & delight it worked and tested fine first time. The sound was glorious compared to what came out out of my Kenwood 9940.
Another unique and informative article on QS and DIY is here:
http://americanradiohistory.com/Archive-Wireless-World/70s/Wireless-World-1976-08.pdf
It is a multi-part article involving QS, SQ, & CD-4. Fun read.
But more to the point: the IC's involved are almost impossible to buy anymore. The circuit is complex and must require factory made PC board.
I suggest you keep up on the upcoming Involve Audio Surround Master (V2?). It doesn't have the Hall or Synthesizer modes that other Sansui units have but by all accounts it is a magnificent upgrade.
Not sure why you would call this a half logic decoder. "Logic" designated decoders we're the province of CBS/SQ. Sansui had Type A or Type B. This design is Type A with F/B and L/R sound discrimination. It is very similar to the Sansui QSD-2.
I purchased & built two of these designs from Bob Coleman at Photolume many years ago. Find the whole article here:
http://www.americanradiohistory.com/Archive-Poptronics/70s/1976/Poptronics-1976-12.pdf
I added a 200Hz Xover 6dB and made a 2 band decoder. The function switch was a nightmare to wire. But as much to my surprise & delight it worked and tested fine first time. The sound was glorious compared to what came out out of my Kenwood 9940.
Another unique and informative article on QS and DIY is here:
http://americanradiohistory.com/Archive-Wireless-World/70s/Wireless-World-1976-08.pdf
It is a multi-part article involving QS, SQ, & CD-4. Fun read.
But more to the point: the IC's involved are almost impossible to buy anymore. The circuit is complex and must require factory made PC board.
I suggest you keep up on the upcoming Involve Audio Surround Master (V2?). It doesn't have the Hall or Synthesizer modes that other Sansui units have but by all accounts it is a magnificent upgrade.
Hi,
Many thanks for your response.
— I called it “half logic” because the article does (in terms of is SQ ability). But may be that is not right.
— In terms of the ICs...unless there are different ones with the same name, I saw some on eBay, for instance, https://www.ebay.com/itm/HA1327-Ori...780461&hash=item43bf09b9ec:g:SfkAAOxy1NxSHOsp
— The PCB is not that much of a problem. I already have a Gerber image / file of it. Then it is a matter of having a service make it. These have come down in price considerably, it seems.
I am curious about your crossover and other modifications. Could you explain a bit more?
Many thanks.
Right you are on that point. I was thinking more in terms of QS ability than SQ.
This is so strange. The very morning before I read your post I had looked for & found the magazine article you mentioned. I then poked around E Bay & found some Vario-Matrix chips. I didn't look far enough to see if a complete set of all needed was available. And who knows if this is good NOS or rejects or whatever. Only one way to find out!
Some mods were made on the board itself. As usual the output blend resistors R53/R66 were clipped. Being a single side power supply there are coupling caps needed everywhere. These are cheapo electrolytic's & I switched out for higher quality film types. I added a higher value power supply filter cap & added a film/ceramic bypass cap at the output side. Exact values I don't remember & I'd have to look at it to refresh my memory. The kit came with all 5% carbon comp resistors & I switched out what I considered critical ones with 1% metal film. Can't tell ya which ones, again I'd have to go & look. Resistor R1 creates the out of phase blending at the two input channels & this is the wrap around synthesizer mode so popular for stereo sources. I removed R1 and wired a 3K ohm resister in series with two of the terminals of a 5K ohm linear pot. This meant when the pot was in the 12:00 position it was very close the original design suggested blend. Counter clockwise there was more anti-phase blend & more rear action. Clockwise & the sound moved more forward.
Off the board I added a selector for more than one stereo source. Then followed an input balance control. From there the signal went into a simple 200Hz 6 dB hi pass filter & 200Hz low pass. Then each went to their individual decoder board. Using two boards meant I needed to change the function switch from 12 pole four position switch to a 24 pole switch. Amazingly I found just what I needed in a electronic surplus mag. It was made for RF switching & had great ceramic section separators and top notch contacts. Wiring this switch was absolutely the hardest part of the project.
The 4 Ch outputs of both boards went into op amp summers to mix the high & low bands back together. From there they went into a 4 gang linear pot for front to back balance and then front and back went into there respective dual pots for front L/R balance and rear L/R balance.
The project went into a former Pioneer spring reverb enclosure. It was just the right size. Black front with white rub on press type made it look as good as how I knew to do back then. Pretty primitive today but at least I didn't resort to Dymo labels.
What I would do different if I did it again. which I won't. Make me too crazy.
Use an input buffer with gain to make up for the 50% signal drop when the L/R input balance pot is centered. After the balance control put a more sophisticated width control to adjust the in/out phase balance of the source material. I think the circuit shown in Fig 2 here would work great:
http://sound.whsites.net/project21.htm
Use 12 dB Xovers but still keep it at 200Hz. After the output balance controls I would add high impedance op amp buffers instead of just sending it straight to the output jacks.
My town was SQ crazy back then. No Sansui anywhere. All the technical articles really made good sense to me there approach seemed so elegant. I had to build this to hear QS Vario Matrix in action. A QSD-1 and then a QSD 1000 followed. But this kit project was real adventure.
What made you think of breaking the frequency range into two like this? Were there such improvements in commercial units or did you think excluding the higher amplitude lower frequencies would improve separation uprange? I will have 5 PCBs ready in a week so I could try a multi decoder down the line.
I was a child overseas when quad came out. I had issues of Popular Electronics and Stereo Review, quad albums (even CD4s) but nothing to play them on. So this is catch up for me!
I have quad reel-to-reels, CD4 cartridges and decoders but no real SQ/QS decoders. I have been listening to SQ albums with the DTS-NEO setting on my AV amp. This will be an eye opener.
I thought of building this back in the day but couldn't really afford it at the time. A couple of years ago I purchased the same unit (on eBay), the Photolume Vista QS100. I recapped it with film types wherever possible. The unit sounds great. It's the exact same circuit as the Sansui QSD-2, it's just missing the output all-pass phase shift circuit, and separation adjustment pots. I think that the lack of the phase shift is a plus as it's only really needed to put decoded QS back in proper phase. For stereo enhance it's better without it. I use it mainly to enhance stereo in the surround mode, I hate the Sansui term "Synthesizer" as all it does is spreads the stereo around the room, nothing is "synthesized" at all! The unit produces natural enhancement of stereo, sort of stereo through a magnifying glass.
Sansui produced the QSD-1 that was a three band decoder. I drew my idea from that. Vario-Matrix enhances the direction of the dominant sound while diffusing the direction of sub-dominant sounds. Using a multi-band decoder doesn't give more overall separation but it does make for a more stable soundfield. Consider the example of a song starting off with a strong bass guitar or low notes on the piano center front, as most bass usually is. Then a screaming lead guitar starts up in right rear & pans around. Multi-band allows these to do that without interfering with each other. On a more subtle aspect the designer can also choose different control voltage filtering with optimized attack/decay for the different frequencies. Slower with more filtering on the bass, less for faster tracking on the higher range. The Involve Surround Master is a three band decoder.
I would expect playing QS or stereo material will be a revelation. For SQ it will be better than DTS NEO but would pale by comparison to a Fosgate 101 or Involve SM. I own the former, not the latter but postings are unanimous that the QS/SQ version of the SM is fantastic.
I am impressed that you have PC boards in the works for this project. Best of luck. Please keep updates coming in & maybe post some pics as it progresses. Pretty cool.
What a find for you. Are you still using it? I agree with the comments on the output phase shift. With such a simple circuit it doesn't do enough to really straighten out the QS phase shifts but probably does enough to degrade stereo imaging. I do have mabey 10 or 12 QS discs but the qualities of Sansui Vario-Matrix to enhance stereo is what really appeals to me. There's an infinite amount of 2 ch stereo out there begging to be listned to in surround. I find all the basic QS, Hall & synthesizer useful depending on the music. For serious projects I'll do up-mixing on my PC & save as DTS or more rently 24/48 uncompressed 5.1 on Blu-Rei.
So, in the end, it turns out I am making a Sansui QSD-2. Of which I already have one...I guess I should have checked before starting!
I will now have FIVE PCBs! Either I have to make a multi channel decoder or...does anyone need PCBs for a nifty project?
Yes I'm still using the Photolum, I also have a QSD-1 installed in another system. I tended to prefer single band processing, always thought that the image was more focused, but after readjusting the QSD-1 and actually finding one bad Phase Discriminator chip I might have to re-evaluate my position on that as the QSD-1 sounds much better now that it's repaired and readjusted.
One abnormality with the Photolum is that left front is out of phase with left back, I'm thinking it might be better to invert the left back phase. Although it sounds fine as is for enhancing stereo. The normal QS output phase shift sort of splits the difference making the phase difference 90 degrees instead of 180 but also throwing the right back phase out by 90 degrees instead of being fully in phase with the front, the correct phase relationship for QS but not so for stereo.
I also purchased an Involve evaluation board. It tests out perfect for QS decoding, but lacks hall and surround which in my books is necessary for stereo enhancement. It (and the Surround Master) could both benefit from Scott Varner (MCS Review) pre-synth circuit, or from Sansui's input circuit.
The boards look great. I'd say higher quality than the originals. What to do with them? Yeah maybe another Photolume. It would be a bit of labor & cost up front to put kits together. I don't know how many people would do this due to purchases of the Involve SM.
Or get creative... An old Quaddie friend of mine loved live rock recordings & video. He thrived on doing his best to create that rock venue sound in his home. He used two QSD-2's to do this. Front left & right speakers we're arranged conventionally. But left back output went to a speaker up front to the left & wide of left front. Same thing for right back on the other side of right front. He operated this unit in synthesizer mode. Any direct hard panned sounds to left or right would pop up in far lft front or right. In the rear he had another QSD-2 in Hall mode with rear speakers arranged as usual. This gave him, literally, a very wide sound stage & he could balance to produce what he liked for rock concert hall ambience in the rear.
That would be me, & I agree. I am amazed that anybody renumbers my articles to MCS Review.
I always thought that if I purchased an Involve SM the first thing (maybe second) I would do is open it up & see what could be upgraded, put it in a different box with the phase balance synth circuit & maybe a few more switch function. There's multiple reasons I never did this but mostly because I have a perfectly functioning Fosgate Tate 101 & QSD-1000. Getting a Surround Master would surely lead to relegating those pieces to the closet & I just like them too much.
Still got your cassette of Doors-Soft Parade encoded via Your Sansui Encoder, R.S.
And thanks to that article you sent me on early Dynaquad decoders and software sponsors....I was able to find a KL Recording disc !
And was shocked that it actually indicated it was dynaquad encoded ! (this was back in mid to early 80's btw )
So thanks, again R .S. ....all much appreciated .
-Derek
Ha! That's great. Thanks for the note! Those things we're completely out of mind until you mentioned them. We have certainly seen many crazy changes in surround sound sound since that old Doors tape. Some even for the better.
Us old quaddies sure have.....and yes much to the best for quad and surround in general .
Many happy improvements .
Nice to know this site has two stellar quadraphiles from the beginnings of the quad era. You and par4ken , that is .
Two knowledgeable , historical quad mates ...that others on here can also appreciate for info .....from the past. :upthumb
Thank you for the kind words. The flip side to that is I am always happy to see someone's post start off declaring to being a Quadraphonic newbie. Or like TopTip who is playing catch on appreciating Quad. Very gratifying to see many years later Surround Sound in general & Quad in particular appeals to newcomers & the younger generation.
BTW TopTip... made any decisions on how you'll proceed?
Not yet. It will be a lot of work and since I found out it is the same thing as the QSD-2, which I have, I lost a bit of the drive to get it done. I should have checked beforehand but at least I learned a bunch of stuff on how to make PCBs the 21st century way, so net-net not really a loss.
In the meantime I ordered an Involve SM (with SQ, the old original version). Look forward to trying it out next weekend.
senorverde
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I'm looking over that article and it seems like it's not totally impossible to build with a PCB, but my question is where the heck do you find a 12 pole, 4 position rotary switch to control each of the decoder's four modes?
This was a superb suggestion! I bought a V1, not to wait for the newer version and I am blown away. I had written off SQ as useless but with this device...it is hard to distinguish it from a true, discrete quadraphonic source.
Many thanks!
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