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Akai SS-1 Universal Synthesizer

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par4ken

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Years ago I built a decoder similar to this from an article in Canadian Audio Magazine "Electron". It simply used a handful of transistors (4 or 8, I forget). The fronts were blended together via a pot in phase the rear out of phase via another pot. It would properly decode EV-4, Dyna, and even QS (RM actually). Normally I would run it with no blend on the front and maximum blend on the rear, but it was interesting to try different settings. The most amazing thing about it was listening to stereo decoded by this device through quad headphones, as the rear blend was increased the sense of space expanded dramatically. Fixler effect anyone.
 

Sonik Wiz

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Years ago I built a decoder similar to this from an article in Canadian Audio Magazine "Electron". It simply used a handful of transistors (4 or 8, I forget). The fronts were blended together via a pot in phase the rear out of phase via another pot. It would properly decode EV-4, Dyna, and even QS (RM actually). Normally I would run it with no blend on the front and maximum blend on the rear, but it was interesting to try different settings. The most amazing thing about it was listening to stereo decoded by this device through quad headphones, as the rear blend was increased the sense of space expanded dramatically. Fixler effect anyone.
I've thought multiple times that a fun little project to build would a simple decoder with complimentary or push/pull control of the blending coefficients. In other words turn the pot to one extreme & you get un-altered stereo in front, full L-R in back. Go the other direction & have full mono blend in front & full stereo in rear. Obviously this could not be used to correctly decode QS/RM because at the mid point the blend would be matched but .5.

My concept was that even with simple decoding for each song (I'm thinking mainly stereo) there would be a sweet spot that matched well that particular mix & music. And one could also do a bit of out of phase blending at the input that could be a useful enhancement.

I said I thought about it. I never got around to trying it cuz I already had too many decoders on hand to play with.
 

par4ken

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Yes but with separate adjustments you could set to .414 for both front and rear. With separate adjustments you can do asymmetrical coefficients like EV-4. That's the reason that I never bothered with an EV-4 decoder is that it was not adjustable and so rather useless in my view, when a fully adjustable one was so simple to build.

Marantz quad receivers had a vari-matrix control (not to be confused with "Vario Matrix") I'm sure that name was used to trick people to think that they were getting proper Sansui decoding as well, in any case it would of been better if the front and back could of been adjusted separately. As it was it was a bit of a joke.

I agree about having too many decoders but this one has me thinking again about headphone listening, playing around with phase is so cool.
 

par4ken

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I've been looking for a small passive decoder for my car such as quatravox or napolex, anyone have better suggestion? (of old passive decoders/adapter that is)
You just have to disconnect from ground the negative speaker wires on the back speakers and connect them together, isolated from ground. That's all the adapters did, they would of had an adjustable resistor in series as well to control the surround level. Those passive decoders were never very expensive, you could keep checking eBay to see if one comes up.
 

furui_suterioo

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I've got two large bags of random car audio equipment from my old car which I never installed in my current car, my plan is to have the rca inputs for all amplifiers and the outputs of the head unit/eq/xover in the glove box with labels so I can rewire them easily as needed from tuner or discrete input from laptop(lol), stereo from phone. I like the napolex because it looks nice and also has Hall switch and I dont have amps installed yet.
 

par4ken

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This thread has peaked my interest, because I can't find the "Electron" article for the decoder that I built, I wanted to see this units schematic. I can't find a service manual download. I did find a copy on eBay though with free shipping for a reasonable price. Most sellers want as much for the manual as the unit is worth in total! If I was to construct one today I would likely use op-amps rather than discrete transistors, I recall that it was a fun project for me in the early 70's.
 

furui_suterioo

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par4ken

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I've never seen one like that, looks like a couple of transformers inside, to isolate the outputs, or to mix the signals? Interesting!
 

chucky3042

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Here 8s a little passive decoder from Australia, (the first surround master?) :)
Pretty sure it used the good ol,l wiring trick with a pot....the Hafner Dynaco style and yes that was my first surround system at around 12 years of age, so it was the first Surround Master!!!!!!

1598571432545.png
 

chucky3042

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And now we are talking the very early "teen age" beginnings of the Surround Master (shameless promotion mode enable). My next attempt at surround was at around the age of 13 in 1971 with an Electronics Australia project (really great magazine died eventually and sorta became the vastly inferior Silicon Chip Magazine) with a simple transistor circuit. This is not exactly it as I would need to dig into my archive of magazines going back to 1969 and I am too lazy. But broadly this is the same sorta thing, I bet this is similar to the circuitry of the Akai SS 1.

1598572049286.png
 

Sonik Wiz

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Pretty sure it used the good ol,l wiring trick with a pot....the Hafner Dynaco style and yes that was my first surround system at around 12 years of age, so it was the first Surround Master!!!!!!

View attachment 55640
Groovy little circuit you've got there. As for the AWA unit it appears to go between the amp & speaker like your set up. But the AWA has 2 largeish xfmr's in there. What do you suppose their purpose is?
 

Sonik Wiz

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And now we are talking the very early "teen age" beginnings of the Surround Master (shameless promotion mode enable). My next attempt at surround was at around the age of 13 in 1971 with an Electronics Australia project (really great magazine died eventually and sorta became the vastly inferior Silicon Chip Magazine) with a simple transistor circuit. This is not exactly it as I would need to dig into my archive of magazines going back to 1969 and I am too lazy. But broadly this is the same sorta thing, I bet this is similar to the circuitry of the Akai SS 1.

View attachment 55642
LOL I can see it coming: Chucky's life story as told by circuitry...
 

chucky3042

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Groovy little circuit you've got there. As for the AWA unit it appears to go between the amp & speaker like your set up. But the AWA has 2 largeish xfmr's in there. What do you suppose their purpose is?
Hmmmm , not sure but I bet your left knacker it was possibly used between the pre and power amp and they were using audio isolation transformers to do the subtraction.........or even if it was speaker level it might be audio isolation transformers as the transformers would not need to handle any bass as that tends to be a common signal and gets cancelled
 
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