Quite a stash to find after all these years!!! As for the NS chips, I have that in my Composer, and it works great. If it's set up correctly with a good stable input signal from a high end cartridge, it's almost impossible to tell the difference from the Exars. But. My understanding, which may not be correct after all these years, was that the NS chips had a flaw in the manufacture, meaning that before the units would work correctly, the factory had to do some workarounds. I thought I heard that you couldn't swap the chips across one for the other because of that. If you unit shipped with an NS it had to stay an NS and same for Exar, although after all this time, I may be wrong.
RARE VINTAGE AUDIONICS OF OREGON SPACE & IMAGE COMPOSER QUAD DECODER UNIT
- Thread starter bigbillquad
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My first Composer has Exar chips and I've had the schematic (which only shows the National chips) for years. I don't notice anything different between the two except for the chips. One oddity is that the supply voltage was changed from + and - 15V to +17V and -13V on my unit and (I presume) all those using the Exar chips. The schematic from Steve Kennedys site still shows the National Chips but has the power supply change, so is it related or not? As I recall one page of the updated schematic shows the Exar part numbers.
The second unit that I purchased a couple of years ago has the National chips, and works fine. I do notice however that at times artifacts are very noticable. Turning down the separation control a bit solves the "problem". Normally I never bothered to adjust the separation control on the other unit that uses the Exar chips, the decoding was always quite smooth.
I understand from reading Steve Kennedy's posts that Exar solved some of the problems of the Nationals but not all of them! I presume that the Fosgate units were designed with the Exars right from the start. He was able to make it perform faster without many artifacts. Substituting the Nationals will likely produce a decoder with noticeable artifacting. He didn't include the separation control to tame the deficiencies of the Nationals.
Steve stated in one of his posts that about one half of the original National Chipped decoders were returned to be updated to the Exars. He also said something about a daughter or adaptor board was used to convert the different pinout of the detector chip. He never mentioned that the latter units had an updated motherboard with the Exar chip pinout.
If you have looked at the schematics, they you are no doubt correct. My info was from Steve and others I talked to at the time, which is more than 40 years ago. My recollection was Steve said that when the NS chips were. delivered, they didn't work, so they had to put together some workarounds, which I took to mean outside the chips, and that was why the chips were not interchangeable. That may be incorrect, and they may in fact be interchangeable.
As I say, mine has the NS chips still, and while it is possible to get some times where you can hear the decoder 'working,' reducing the Separation control to the 3:00 position cures it. It is rare that I ever notice it any more now that I have a much better front end, that is cart and table, or perhaps my ears have gotten lazy.
As I say, mine has the NS chips still, and while it is possible to get some times where you can hear the decoder 'working,' reducing the Separation control to the 3:00 position cures it. It is rare that I ever notice it any more now that I have a much better front end, that is cart and table, or perhaps my ears have gotten lazy.
The workarounds were used with both sets of chips. The Interface Circuit (Audionics), Directional Control Circuit (Fosgate) were necessarily connected between the Direction Detector chip and the Matrix Multiplier chips. Had both sets of chips been designed properly the workaround would have not been required at all. Decoders could have been manufactured much more inexpensively!
The Audionics circuit was developed using the National chips, I don't think that any changes were made with the switch to the Exars. Jim Fosgate would have designed his using the Exars right from the start. His circuit differed and I presume allowed the Exars to operate a bit faster, and he tweaked it for greater separation. I don't have a Fosgate to compare but my guess would be that the Audionics produces smoother decoding
I agree that backing off the Audionics Separation control cures any artifacting.
After a year or so of buying and having put in the quad closet, I integrated 2 Zektor switches. The 4.1 takes all the vintage processors and the SM, and the 7.1 takes my Anthem and the feed from the 4.1. So fun!!
Check out the Composer. When I first got it about 6 months ago or so, it had a very high noise floor. After 50 years, I'm not surprised. It bothered me, so I stuck it on the shelf. I brought her back, and it is a really nice processor. Definitely gets the cool factor trophy. I don't care about the noise now....
And I had not realized, it is an original Wurly scope...way cool. And all the control with the Composer. The QSD-1 is so drab by comparison! Lol.
And after only a short listening time, I can hear why @par4ken has high regard for the S&IC.
Check out the Composer. When I first got it about 6 months ago or so, it had a very high noise floor. After 50 years, I'm not surprised. It bothered me, so I stuck it on the shelf. I brought her back, and it is a really nice processor. Definitely gets the cool factor trophy. I don't care about the noise now....
And I had not realized, it is an original Wurly scope...way cool. And all the control with the Composer. The QSD-1 is so drab by comparison! Lol.
And after only a short listening time, I can hear why @par4ken has high regard for the S&IC.
I am with you, but then my S&IC has been the heart of my system since I bought it new in 1979. For SQ it is still my favorite decoder. Not perfect if you don't set it up fairly carefully, but once it's locked in it's remarkable.
When playing stereo source, the out of phase material goes to the back, which is largely Hall effect, if you will, but also in enhance you get the bending of the sound field so it simulates surround.
That said, I would love a QSD-1. Any day, every day. Of course they are the gold standard for QS, but they do a terrific job with stereo. It's different in how it gives a surround effect from the Audionics unit, but I really like it. And it does it without worrying about any decoder artifacts. If I could afford one, I'd have both, but since I can only afford one, it's the S&IC.
It shouldn't be noisy. I would try spraying or DeOxing the pots. The Tate II that I recently purchased was noisy, cleaning the pots fixed it. I would also replace the coupling capacitors, lots of room for some film types there.
Thank you for the recommendation. I'll make that a to-do for that piece. It's fantastic and if I can rid that hiss...
Correcting my previous post. The Tate II does run it's op-amps in class A like the S&IC. Not shown on the schematic the unit has 4.3K pull-up resistors on the output of the op-amps. I discovered that fact when I looked inside mine. The S&IC uses 2.2K forcing a bit more current (and heat). Does it actually improve the sound over "naked" op-amps, I can't say for sure but it is an "audiophile" tweak that doesn't cost much to implement.
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