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Akai SS-1 Universal Synthesizer

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par4ken

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Agreed but the common bass signal typically cancelled out L-R so the rear speakers really did not need to be full range making the technique suitable to the satellite speaker concept. A good reason to make bass common in recordings is to get the benefit of 2 sets of drivers working together to push enoigh air to extend the bass, in addition to the wrong myth that bass is non directional below 150 Hz . Our tests showed that on sine wave pure tone bass is actually non directional to 800 Hz but on band limited pink noise was totally directional down to 35 Hz!! Explains why I can always point to where the subwoofer is for the first 30 seconds before my brain masks the position.
I recall years ago having either a woofer failure or a loose wire, I was amazed that I didn't notice it at all at first. One time I was toying with the idea of separate woofers and mid/tweeters mounted in separate enclosures. That experiment showed that the drivers had to be placed close together or they didn't sound right at all.
 

par4ken

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I worked out a simple decoder using op-amps similar to the transistor based one that I built years ago. All you need is one quad op-amp, two dual pots and a bunch of equal value resistors.
I'll share the design once I have a chance to redraw it. Anyone know of an easy to use free CAD program for making schematics? Anyway all you need do is configure two op-amps as non-inverting summing amplifiers, the other two as differential amplifiers. You mix the say left with the right from the pot, and vice-versa. For a more complete project you could get fancy and add input buffering, input balance and maybe input level and output level controls if required/desired.
 

Sonik Wiz

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I worked out a simple decoder using op-amps similar to the transistor based one that I built years ago. All you need is one quad op-amp, two dual pots and a bunch of equal value resistors.
I'll share the design once I have a chance to redraw it. Anyone know of an easy to use free CAD program for making schematics? Anyway all you need do is configure two op-amps as non-inverting summing amplifiers, the other two as differential amplifiers. You mix the say left with the right from the pot, and vice-versa. For a more complete project you could get fancy and add input buffering, input balance and maybe input level and output level controls if required/desired.
Mouser & Digikey offered free schematic drawing apps. There' quite a bit of difference between them so check both out.
 

par4ken

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So hear is my proposed decoder /synthesizer. All resistors must be the same value, anything from 10K to 100K should be fine. The pot could be lets say 20K to 100K either log/audio or linear, dual ganged. The advantage of a linear pot would be that a mid setting would correspond to a mixing coefficient of 0.5, likewise other settings could be estimated by the position of the dial.
 

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Sonik Wiz

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So hear is my proposed decoder /synthesizer. All resistors must be the same value, anything from 10K to 100K should be fine. The pot could be lets say 20K to 100K either log/audio or linear, dual ganged. The advantage of a linear pot would be that a mid setting would correspond to a mixing coefficient of 0.5, likewise other settings could be estimated by the position of the dial.
Yup looks like decoder to me! Are any of those pots meant to be ganged?

What design app did you use? Looks great. You must be a quick learner as I had quite a bit of learning challenge when I tried that. I just don't remember if I used Mouser or Digikey...
 

par4ken

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Yup looks like decoder to me! Are any of those pots meant to be ganged?

What design app did you use? Looks great. You must be a quick learner as I had quite a bit of learning challenge when I tried that. I just don't remember if I used Mouser or Digikey...
Yes as stated in the text the unit uses 2 dual ganged pots, I couldn't figure how to show that they were ganged in the CAD app. I used the one from Digi-key I couldn't find the one from Mouser. I tried to go to the Mouser.com site but it knew my IP was from Canada and kept sending me back to Mouser.ca, although I would think that it should be posted on both sites.
Anyway I'v always liked Digi-key, they are just across the border in Thief River Falls.
 

MidiMagic

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That schematic from my UQ-44 is just the 90 degree phase shifter. You don't have the rest of the decoder.
 

par4ken

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So here is the schematic of the Akai SS-1. The actual decoder/synthesizer circuit is very similar to the one that I built years ago. They include adjustment trimmers for the rear outputs to maximize rejection of common in phase signals (vocals), not sure that's necessary unless the parts tolerance are not very tight (likely the case). It includes a phono pre-amp, which might actually make it useful for some today that lack that feature. The unit also includes a mostly unnecessary output amplifier consisting of 3 transistors per output channel. I've uploaded the entire manual to hifiengine.com so check there in awhile if you want to download it.
 

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chucky3042

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So here is the schematic of the Akai SS-1. The actual decoder/synthesizer circuit is very similar to the one that I built years ago. They include adjustment trimmers for the rear outputs to maximize rejection of common in phase signals (vocals), not sure that's necessary unless the parts tolerance are not very tight (likely the case). It includes a phono pre-amp, which might actually make it useful for some today that lack that feature. The unit also includes a mostly unnecessary output amplifier consisting of 3 transistors per output channel. I've uploaded the entire manual to hifiengine.com so check there in awhile if you want to download it.
Stone age stuff! But lots of fun
 

Soundfield

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So hear is my proposed decoder /synthesizer. All resistors must be the same value, anything from 10K to 100K should be fine. The pot could be lets say 20K to 100K either log/audio or linear, dual ganged. The advantage of a linear pot would be that a mid setting would correspond to a mixing coefficient of 0.5, likewise other settings could be estimated by the position of the dial.
I'm often asked to make line level Hafler boxes for friends, and so next think I'll try using the rear channel half of your circuit - not sure I've any real need for the front half as the ability to reduce image width on purely stereo source material is of little value I suspect. I've a duff Sony SQD-2070 whose little case would be just the right size to house it and a power supply.
 
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