Akai SS-1 Universal Synthesizer

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Soundfield

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Here is a list of all EA projects (I will have them somewhere!)- just ask
Hi Chucky -
I uncovered reference to what I think might have been a valve based (!) 2-4 ch convertor in the August 1972 issue of Electronics Australia. The article was entitled "Economical Quadraphonic Adaptor". I've only been able to find the contents page-
P1030219.JPG

Would love to see it if you have a copy of that issue. Cheers!
 

Sonik Wiz

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Hi Chucky -
I uncovered reference to what I think might have been a valve based (!) 2-4 ch convertor in the August 1972 issue of Electronics Australia. The article was entitled "Economical Quadraphonic Adaptor". I've only been able to find the contents page-
View attachment 61934
Would love to see it if you have a copy of that issue. Cheers!
Well it took some digging but here ya go:


Yup a 12AU7 based quad decoder suitable for QS/RM, EV, stereo, but not so much SQ.
 

Soundfield

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Well it took some digging but here ya go:


Yup a 12AU7 based quad decoder suitable for QS/RM, EV, stereo, but not so much SQ.
Thanks muchly Sonik!
Strangely, I'd looked on that site previously but couldn't find it for some reason, glad you did.
It's pretty much what I'd expected, just a couple of differential pairs, but will put it on the 'to do' list anyway. Rather worryingly though it comes with a somewhat cryptic warning-

note.JPG

so it might not be an entirely straightforward build!
 

chucky3042

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Thanks muchly Sonik!
Strangely, I'd looked on that site previously but couldn't find it for some reason, glad you did.
It's pretty much what I'd expected, just a couple of differential pairs, but will put it on the 'to do' list anyway. Rather worryingly though it comes with a somewhat cryptic warning-

View attachment 61942
so it might not be an entirely straightforward build!
Thanks Sonik

Beat me! Oh its a pretty useless crap circuit.
Great memories, it was a great magazine
 

Soundfield

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After a bit of a diversion onto other things, I finally got around to the completion of the modern synthesiser / decoder inspired by the Akai. It has been so long that I’d used the PSU I’d constructed for it in another project (!) so used a proprietary one instead, although it’s far bigger than necessary. However, it all came together reasonably neatly in that old salvaged Sony case……

SD1.JPG


SD2.jpg


SD3.jpg


It all tests OK, just need to hook it up and give it a listen now.
 

Sonik Wiz

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After a bit of a diversion onto other things, I finally got around to the completion of the modern synthesiser / decoder inspired by the Akai. It has been so long that I’d used the PSU I’d constructed for it in another project (!) so used a proprietary one instead, although it’s far bigger than necessary. However, it all came together reasonably neatly in that old salvaged Sony case……

View attachment 64535

View attachment 64536

View attachment 64537

It all tests OK, just need to hook it up and give it a listen now.
Nice build! What was the box you used? But I must say a few more knobs & blinky lights might add some value...
 

par4ken

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Here is my decoder. I used a salvaged steel chassis, power supply card, transformer, line filter as well an 1U Hammond Aluminum Rack Panel (originally purchased in the early/mid eighties) and never used.

As I often do I constructed a second project in the same box (more about that one latter).

This decoder definitely out preforms my original transistor based unit. I swapped out the TL074 op amp with the LME49740NA; an op-amp with crazy specs, like 120 dB CMRR and 0.00003% distortion! I built the decoder primarily for quad headphone listening (from stereo sources). It does do a nice job of that, it sounds much better than plain stereo through the same phones. As you dial up the rear (out of phase blend) the spaciousness greatly increases, to the point where you have to back it off a bit, then add a bit of in phase blend to the front channels, to keep the vocals intact.
100_0921.JPG

I prefer to use the type of quad phones with the drivers separated length wise (horizontally). The phones from Koss all have the drivers stacked vertically, while the Koss phones do produce a bit more active sound field than you get with plain stereo the effect is not nearly as good as with the other type phones.

I did a bit of listening over the speakers as well and was amazed by just how good this simple decoder could sound. Because the other project used up all the space on the rear of the chassis I mounted the input/output jacks on the front. That arrangement makes patching it in and out of my system a breeze.
 

Sonik Wiz

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Here is my decoder. I used a salvaged steel chassis, power supply card, transformer, line filter as well an 1U Hammond Aluminum Rack Panel (originally purchased in the early/mid eighties) and never used.

As I often do I constructed a second project in the same box (more about that one latter).

This decoder definitely out preforms my original transistor based unit. I swapped out the TL074 op amp with the LME49740NA; an op-amp with crazy specs, like 120 dB CMRR and 0.00003% distortion! I built the decoder primarily for quad headphone listening (from stereo sources). It does do a nice job of that, it sounds much better than plain stereo through the same phones. As you dial up the rear (out of phase blend) the spaciousness greatly increases, to the point where you have to back it off a bit, then add a bit of in phase blend to the front channels, to keep the vocals intact.
View attachment 66045
I prefer to use the type of quad phones with the drivers separated length wise (horizontally). The phones from Koss all have the drivers stacked vertically, while the Koss phones do produce a bit more active sound field than you get with plain stereo the effect is not nearly as good as with the other type phones.

I did a bit of listening over the speakers as well and was amazed by just how good this simple decoder could sound. Because the other project used up all the space on the rear of the chassis I mounted the input/output jacks on the front. That arrangement makes patching it in and out of my system a breeze.
Nifty looking box o' goodies! And pretty interesting info on how you use it for headphones. I see 8 pots/switches but only 2 with knobs???. What do they do?

Edit: Oh. A closer look shows the other items to be your 2 in / 4 out jacks. Unique for a front panel.
 
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par4ken

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Nifty looking box o' goodies! And pretty interesting info on how you use it for headphones. I see 8 pots/switches but only 2 with knobs???. What do they do?
There are two knobs (on front) which control the 2 ganged pots, one for front blend the other for the back blend. The decoder outputs are simply plugged into a quad amplifier or (quad or stereo x2) headphone amplifier. As previously stated front in phase blend is used on one pair of outputs (front) and out of phase blend is used on the other (back) pair. Use of Quadraphonic phones is obviously required. The stuff on the back is wholly another project.

The stuff on the back is my attempt to convert one of my eBay bargains into a slightly more useful unit. Some time ago I purchased a RSP Circle Surround Encoder. It cost me very little money but it is only the 4.0 type. Unfortunately It's not the what would be the much more useful 5.2.5 encoder, in fact I don't recall ever seeing one of those for sale on eBay.

It would be best described as an improved Dyna diamond encoder or a stripped down (for the better) Dolby Surround Encoder. As such it has only left, right center and surround inputs. By feeding the left and the centre the same signal simultaneously it will produced a left front encoded output that decodes via a Circle Surround or a QS decoder. Same for the right channel, the encode is perfect RM. It works for the rear channels as well by feeding left to the left input and surround input simultaneously. The rear encode is not perfect RM (QS) however nor is it perfect Circle Surround either. Signals are still decoded from the proper position but at slightly reduced separation. I'm still playing/experimenting with it. Because it has only one all pass phase network instead of two, the encoded rear signal will have a phase shift of about 35° if you were to pan across the rear the phase will increase to 90° at centre back. The right side changes from -35° (back corner) to -90° at center back. This incorrect phase is responsible for the less than perfect result.
The Encoder has balanced inputs, I'm making use of the inverting side for the four corner inputs, fed from inverting op-amp summing amplifiers. The non inverting inputs are routed to RCA input jacks so that I retain the full functionality of the original unit.

This is a project mostly for fun, I need to do more testing to see if the encodes would actually useful for anything. I know that encoding via software instead will produce perfect QS or SQ results, I've done it before. The Involve encoder unit is also very intriguing.

Or I could patch the sound decoders rear output (from the front panel jacks) to the left and right of the encoder to encode the rear in true RM.
 

par4ken

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that is definitely cool. would that i could get a talented hobbyist such as yourself to repair/refurbish my unit.
What unit do you have? I don't mind doing work for others but you would have to get the unit to me somehow. It's not ideal to have to ship back and forth, and across boarders.. Perhaps I can simply make some suggestions for you, if I know just what we are looking at.
 

abby normal

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akai ss1 universal synth. mine is showing its age, in the rear matrix mix pot [proportion of surround to stereo], seems to be a hitch in there somewhere in the part of the knob's travel to the transition point between pure stereo and pure [but decorrelated] surround. the volume just drops out intermittently at that point even if i twiddle the knob back and forth several times. no audible static like it would be if it needed some tuner cleaner in there. i suspect it is a fault in the decorrelation circuit. but i am no electronics whiz so i can't say for sure.
 

par4ken

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akai ss1 universal synth. mine is showing its age, in the rear matrix mix pot [proportion of surround to stereo], seems to be a hitch in there somewhere in the part of the knob's travel to the transition point between pure stereo and pure [but decorrelated] surround. the volume just drops out intermittently at that point even if i twiddle the knob back and forth several times. no audible static like it would be if it needed some tuner cleaner in there. i suspect it is a fault in the decorrelation circuit. but i am no electronics whiz so i can't say for sure.
The first thing to try is to spray the pot with contact cleaner, or a couple drops of Deoxit (comes in a small tube). If that doesn't work then look for a replacement pot. Looking at the manual the pots are all panel mounted, replacement should be a breeze for anyone with half decent soldering skills. Looking on eBay I see several that should work, assuming you want to keep the original knobs. If you don't mind replacing the knobs as well you have even more choices. The pot is specified at 10K linear taper, I see no reason that even a 50K linear couldn't be substituted if need be.

I love the way all the components are spread out on the PC boards, it's crying out for a capacitor upgrade. WIMA makes small polyester film capacitors that will easily fit to replace the electrolytic coupling capacitors. I did a quick eBay search and all the required values are available from various sellers. The power supply capacitors could/should use replacement as well. Modern electrolytics are smaller than the vintage types and so could be replaced with larger values as well. I'm not saying that a capacitor upgrade is necessary, but that it is a good idea. I remember it once being said that electrolytic capacitors only last for 20 years at best. Vintage quad stuff is twice that age and much of it is still going strong!
 

Soundfield

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I love the way all the components are spread out on the PC boards, it's crying out for a capacitor upgrade. WIMA makes small polyester film capacitors that will easily fit to replace the electrolytic coupling capacitors. I did a quick eBay search and all the required values are available from various sellers. The power supply capacitors could/should use replacement as well. Modern electrolytics are smaller than the vintage types and so could be replaced with larger values as well. I'm not saying that a capacitor upgrade is necessary, but that it is a good idea. I remember it once being said that electrolytic capacitors only last for 20 years at best. Vintage quad stuff is twice that age and much of it is still going strong!
Yes Ken, the SS-1 would make a fun restoration project. Easy layout to work on. I thought it was fully transistorised but see that it does also have a couple of 9 pin (!) “Integrated circuits” – LD3130 “hybrid amplifiers” – which are pretty difficult to find should you need one! They don’t seem to do anything special and I wonder why Akai used them (rather than a handful of additional transistors)? Sadly I’ve never seen an SS-1 offered for sale on this side of the pond.
 
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