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 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.
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 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
I am curious about your crossover and other modifications. Could you explain a bit more?
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.
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.
Has anyone on the forum built the half logic decoder on the below image? Any views about it? Thinking of building one.
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 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 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?
It (and the Surround Master) could both benefit from Scott Varner (MCS Review) pre-synth circuit, or from Sansui's input circuit.
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.
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.
Nice to know this site has two stellar quadraphiles from the beginnings of the quad era. You and par4ken , that is
BTW TopTip... made any decisions on how you'll proceed?
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.
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