RARE VINTAGE AUDIONICS OF OREGON SPACE & IMAGE COMPOSER QUAD DECODER UNIT

[Sonik Wiz]

You wont hear any difference (you will think you do!)

Quoting J. Gordon Holt is always provocative. But I've done it before I guess I will do it again...
because of his standing almost everyone he encountered asked about neoprene vs latex TT belt drives, speaker & line level cables, and room acoustics. They all asked "does this affect the quality of sound?" His reply was: "many things affect the quality of sound in audio reproduction. The only thing that matters is if you can hear it or not."

 

[par4ken]

I'm listening to the crippled decoder now sans resistors and it sounds very good, excellent in fact. Throughout my years of this audio hobby I have used the TL074 the most often. I never bothered with class A biasing. later on I started adding the pull up resistors to some projects based largely on POOGE articles. I remember using much higher values like 6.8 or 7.1K. Did it noticeably improve the sound? I don't think so. Did it hurt the sound? I'm sure that it did not. Do these new "perfect" op-amps have anything to gain by class A operation? I can't see how but more importantly can it actually hurt the sound by forcing so much extra current through the output stage? That is the big question. The data sheet makes no mention of what is inside, no simplified schematic like the old data sheets always had. So we are operating blind.

It is best to connect the resistor or current regulator to the negative supply forcing the NPN output into class A. So why did Audionics connect some chips to the positive supply forcing the chip to use the (inferior) PNP output transistor? My guess is that they wanted to equalise the current draw on both rails.

Could the class A operation be improved by using a current regulator? Without doing listening tests I believe that it could be. If I was keeping the original op-amps I would give it a try for sure. The mod would be very easy with the resistors gone, just solder the current regulator into the same holes.

So I'm thinking that I will update all the decoders with the new op-amps and remove the resistors. Then if I get the urge to experiment I'll do it with the crippled unit.

 

[Marcsten]

My third Composer is functional with the exception of the DES direction sensing chip. I'm thinking of just using it mainly for the Axial Tilt circuit. With my current recording set up I go through the Composer using the tilt correction then to the computer's sound card input. The problem that I have is that when I play the recording during editing via the same audio editor I get some low level feedback as the sound cards inputs are still active. It is a pain to have to disconnect the input cables or mute the inputs via the sound cards control panel.

When I first got my original Composer I wrote Steve Kennedy suggesting among other things that the unit should have a tape monitor. That would have added cost to the already expensive product. Most vintage decoders do have a tape monitor (most useful if you have a three head machine). Even if the tape output was switchable would be a useful feature, but I digress.

Why use the Axial tilt anyway? For years I didn't bother as it is such a pain to adjust, most test records have test tones that are far too short, and the pots are awkwardly placed on the back of the unit. I started using it a couple of years ago.

With my Sony cartridge I was able to improve separation from just over 20 dB to almost 30 using the tilt circuit! Using the new Audio Technica cartridge the improvement was less, a few dB maybe. When listening to stereo that improvement is not even noticeable. It did seem to have the biggest effect when tilt corrected recordings were decoded with other (lesser) decoders. The tilt correction circuit is similar to Sonics pre-synth/phase balance circuit, just that it operates over a much smaller range, adjusted to cancel out the crosstalk in the opposite channel. It would be a very easy DIY project.

The S&IC comes stock with TL074 quad op-amps. To tweek better sound out of them Audionics ran them in Class A. That was done by means of a 2.2K resistor from each op-amps output to the negative or in some cases the positive supply rail. Over the years I swapped op-amps to the AD713. Close enough to the TL074 that the mod is likely still a good fit. I tried the OPA4123PA but they were unstable, I don't know if that was because of their wide bandwidth or because I bought them from a Chinese seller and so may be fakes! More recently I bought some LME49740 from a U.S. seller depleting his supply. Sadly the LME49740 has been discontinued. There are lots for sale from China at attractive prices but they are likely fakes. I just ordered some more LME49740 from a U.K. seller. I used one to make my active adjustable Dyna type decoder, they have an incredible CMRR (typical 120 dB), blending the stereo signals out of phase with each other using one of these almost totally eliminates the vocal. That attribute has got to be a plus in a matrix decoder! They seem to work/sound fine simply dropped into the Composer. I'm in a bit of a Dilemma, is class A operation beneficial with this op-amp? It has such low distortion already, it is possible that the added resistors are now degrading performance?

Audionics glued heatsinks to the chips running class A as they do run warm. The Composer with the old National chip set has no heatsinks on the chips. I guess that it was an afterthought.

As a test I removed the resistors from the crippled (third) Composer and installing my last LME49740 the rest are AD713 and one TL074 . It still sounds fine to me with mostly the old op-amps still installed and no class A.

I intend to upgrade all units by substituting the LME49740. My dilemma is do I leave in the resistors and hope for the best. Do I remove them from all units still hoping for the best. Do I replace the resistor with a JFET, JFET Cascode, Current Regulating Diode or change it's value, 2.2K always seemed rather low. What current is optimum, is this class A thing totally unnecessary. I'm leaning toward the latter.

Here is a very interesting link about Class A biasing of op-amps.

https://tangentsoft.com/audio/opamp-bias.html

As Steve Kennedy from Audionics told me several times, the performance of the Composer is totally dependent on what you have ahead of it. So if your turntable/cart setup doesn't provide accurate phasing for whatever reason, then the axial tilt will never seem to be correctly set up. Performance will still be excellent, IMO, but not as sharp. Sounds like that might be what you experienced. I had the same experience over the years. With my current much better setup, I can certainly hear a difference in separation after setting the axial tilt. Of course I do have to play the tones several times, as you say.
As for Class A, well, some people say they can hear the difference, while others don't. It's a high end stereo thing. Let's not start that again (think, cables). Certainly IF there is an audible difference, if the Composer is connected to non-Class A gear, as is the case for pretty much all of us, the Class A of the Composer is certainly lost, if there is any difference. I speculate the Composer being Class A was an effort to make it appeal to higher end folks, which is a debatable strategy under the circumstances.
Whenever I hear about all the stuff with crippled Composers, I thank my lucky stars that my very early National Semiconductor unit bought back in 1979 still works perfectly. It was recapped many years ago by Quad Bob, but it has always performed flawlessly, testament to its build quality. Of course since I have owned it from new I know it has never been abused.

 

[par4ken]

As Steve Kennedy from Audionics told me several times, the performance of the Composer is totally dependent on what you have ahead of it. So if your turntable/cart setup doesn't provide accurate phasing for whatever reason, then the axial tilt will never seem to be correctly set up. Performance will still be excellent, IMO, but not as sharp. Sounds like that might be what you experienced. I had the same experience over the years. With my current much better setup, I can certainly hear a difference in separation after setting the axial tilt. Of course I do have to play the tones several times, as you say.
As for Class A, well, some people say they can hear the difference, while others don't. It's a high end stereo thing. Let's not start that again (think, cables). Certainly IF there is an audible difference, if the Composer is connected to non-Class A gear, as is the case for pretty much all of us, the Class A of the Composer is certainly lost, if there is any difference. I speculate the Composer being Class A was an effort to make it appeal to higher end folks, which is a debatable strategy under the circumstances.
Whenever I hear about all the stuff with crippled Composers, I thank my lucky stars that my very early National Semiconductor unit bought back in 1979 still works perfectly. It was recapped many years ago by Quad Bob, but it has always performed flawlessly, testament to its build quality. Of course since I have owned it from new I know it has never been abused.

That is what I've been saying forever, that the S&IC is the most neutral sounding decoder ever. What goes in comes out. Replacing the electrolytic coupling capacitors with film types makes it even better. Yes the class A operation would have been done in part to appeal to the high end crowd. I think that they did the same with their preamplifiers. That is not to say that it is not a valid idea. The LME49740 op-amp is miles above the old TL074 in distortion, CMRR, and is quiet enough to use as a phono preamplifier. So are the class A resistors still serving any purpose at all (in a modified unit) or are they actually a detriment?

I have no problem adjusting the tilt circuit, I like to use a scope so that you can see when the crosstalk is at minimum. It is just that the tones on most records are rather short, especially the Audionics one. Listening to music while pushing the tilt button in or out makes no noticeable difference to me, not to say that it is impossible to hear under all conditions. The main point of the tilt circuit is to help provide the best most balanced SQ encoded source possible to the decoder.

 

[chucky3042]

That is what I've been saying forever, that the S&IC is the most neutral sounding decoder ever. What goes in comes out. Replacing the electrolytic coupling capacitors with film types makes it even better. Yes the class A operation would have been done in part to appeal to the high end crowd. I think that they did the same with their preamplifiers. That is not to say that it is not a valid idea. The LME49740 op-amp is miles above the old TL074 in distortion, CMRR, and is quiet enough to use as a phono preamplifier. So are the class A resistors still serving any purpose at all (in a modified unit) or are they actually a detriment?

I have no problem adjusting the tilt circuit, I like to use a scope so that you can see when the crosstalk is at minimum. It is just that the tones on most records are rather short, especially the Audionics one. Listening to music while pushing the tilt button in or out makes no noticeable difference to me, not to say that it is impossible to hear under all conditions. The main point of the tilt circuit is to help provide the best most balanced SQ encoded source possible to the decoder.

 

[chucky3042]

Severe bias alert!

I tried the Tate at Rustyandi home dungeon on a non instant A/ B basis against the SM and I and Dave the ***** could pick the difference every time (Rustyandi could not). The difference was a fuzzyness in the apparent distance of the image- not the position. The SM was more precise.

But I am of dodgy character.

 

[chucky3042]

The Surround Master may well be better than the Tate.
Nonetheless, a lot of the Kewl Kids around here have Tates.

As I have frequently said, I am not to be trusted and am totally biased!!!!

 

[par4ken]

The Surround Master is not better than the Tate! I'm not wanting to get into that comparison or debate of decoder ability right now. I'm just talking about sound quality! What goes in comes out, it doesn't add any flavour or colouration of it's own.

 

[chucky3042]

The Surround Master is not better than the Tate! I'm not wanting to get into that comparison or debate of decoder ability right now. I'm just talking about sound quality! What goes in comes out, it doesn't add any flavour or colouration of it's own.

 

[quadaholic]

Well, I bought the Composer that was on ebay last week. So far, all the lights work, appears to decode test tones and made decent work of the ELP king biscuit cd I played through it for a couple of minutes last night. I definitely need to sit with it an and have a more discriminating listen, but so far it seems to be promising. I'd like to know about recapping, as I'd like to get that taken care of here in Boston. I know some good techs, but I'd need some direction on what caps to get. I'm not looking to do any big changes to the unit. I just want to get it up and running so I can put it to work. The serial number is 127, and the chips have nine legs, so I expect they are the original national semiconductor ones. Thanks in advance for any guidance that can be offered while I dig through the thread. I can post pics if that helps.

 

[par4ken]

I always recommend replacing electrolytic coupling capacitors with a film type. these are what I used on my composers and my QSD-1. You will require 10 of them.

https://www.ebay.ca/itm/304073765397
Feel free to use anything that will fit. You can (optionaly) bypass the 10µF with a small (.01µF) polystyrene. The small capacitor can fit below the 10µF soldered to it's leads.

The power supply takes four 2200µF 35V electrolytics, I used 3300µF 50V. Modern capacitors are smaller than the originals so you can up their values a bit. Also need two 220µY 25V. There are six 50µF used for the display. Don't up those values unless you want to slow down the display action. They aren't that important you can leave them alone if you wish there are also three 1µF caps used for the level detector. Again replace them or not. I like to get the electrolytics from a reputable supplier like Digikey.

https://www.digikey.com/
Schematics can be found here.
http://www.pacair.com/audionics/Composer/Schematics/index.htm
more info here
https://www.quadraphonicquad.com/forums/threads/audionics-of-oregon-space-image-composer.27928/

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[quadaholic]

I always recommend replacing electrolytic coupling capacitors with a film type. these are what I used on my composers and my QSD-1. You will require 10 of them.

https://www.ebay.ca/itm/304073765397
Feel free to use anything that will fit. You can (optionaly) bypass the 10µF with a small (.01µF) polystyrene. The small capacitor can fit below the 10µF soldered to it's leads.

The power supply takes four 2200µF 35V electrolytics, I used 3300µF 50V. Modern capacitors are smaller than the originals so you can up their values abit. Also need two 220µY 25V. There are six 50µF used for the display. Don't up those values unless you want to slow down the display action. They aren't that important you can leave them alone if you wish there art also three 1µF caps used for the level detector. Again replace them or not. I like to get the electrolytics from a reputable supplier like Digikey.

https://www.digikey.com/
Schematics can be found here.
http://www.pacair.com/audionics/Composer/Schematics/index.htm
more info here
https://www.quadraphonicquad.com/forums/threads/audionics-of-oregon-space-image-composer.27928/

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Just rolled out of bed and am reading this . Thank you very much for the pointers. I'll start digging into this as soon as I get home from work tonight.

 

[par4ken]

The Fosgate Research Tate II Surround Sound 101A is still for sale. Just like with the Surround Master there are many that say that it is better than the Audionics. From what I understand is it operates a bit faster due to Jim Fosgates interface circuit which differs from the S&IC.

https://www.ebay.com/itm/2041869677...Xfiv55YCPuTlgiKBgs8In6/hE=|tkp:Bk9SR7r15s_HYQ
On the other hand it does not have it's op-amps running in class A. They used the higher noise TL084 instead of the TL074. It has a six pole phase shift network the S&IC has an eight pole one. Switching is done via (slightly nonlinear) 4066 CMOS Analog Switches instead of the mechanical ones used by Audionics. Also the Composer is in a nice rack mount case with directional display and includes a soft clipping circuit.

There is a matching "Audionics of Oregon RS-1 Pre-Amplifier" for sale now as well. From what I recall it has class A op-amps as well plus the axial tilt adjustment controls are placed on the front so that it is easy to adjust. I would not pay near that price for it, you can see from the pictures that there is not a whole lot to it. Hell no tone controls! Audionics was a bit ahead of its time in realising that many Hi-end users do not use them.

https://www.ebay.com/itm/1853038745...clg9LgEpssZEHoGCSV77MYXo4=|tkp:Bk9SR7r63tDHYQ

 

[Owen Smith]

I'd prefer the S&IC on those grounds. Eight pole filter in the phase shift network rather than six is a considerable improvement, plus the lower noise op amps. Not sure how much the analogue switches slight non linearity would matter on the Tate. I also much prefer the looks of the S&IC.

The only thing the Tate has going for it is the slightly faster response, and frankly sometimes that's a good thing and sometimes it's a bad thing depending on the audio being decoded.

 

[par4ken]

I'd prefer the S&IC on those grounds. Eight pole filter in the phase shift network rather than six is a considerable improvement, plus the lower noise op amps. Not sure how much the analogue switches slight non linearity would matter on the Tate. I also much prefer the looks of the S&IC.

The only thing the Tate has going for it is the slightly faster response, and frankly sometimes that's a good thing and sometimes it's a bad thing depending on the audio being decoded.

I'm not certain just how that higher speed could have been achieved as the control signals still originate from the same chip. I seem to recall something about the Fosgate being better on diagonal splits as well. Jim encased his circuit in epoxy so as not to reveal any of its secrets.
He did the same thing with some of his later Dolby and "Space Matrix" decoders.

 

[par4ken]

Drifting a bit off topic, I came across this on eBay today. It's the same unit as the Audionics 106C. Audionics actually imported thiers from the UK. The "Connaught FCD 06-1" was sold in the UK. I had the bare decoder board (the 106A), imagine the heavily populated portion of the larger board chopped off from the rest. The 106B was the larger board with no case. I had forgot that they used DIN connectors rather than RCA's. They save a lot of panel space that way and DIN was for a time the standard in Europe.

This is the first that I've ever seen one eBay. I'm so tempted for nostalgic reasons but the shipping is a killer! With discrete components it is easily fixable if non functional. It has no enhancement logic it's just basic SQ with switchable 30% rear blend.

https://www.ebay.com/itm/1659573445...0&_trksid=p2351460.c100667.m2042#readMoreDesc

 

[par4ken]

There is currently an auction on eBay for an Audionics BT-1 Preamplifier. Unlike the RS-1 Pre-Amplifier that also is for sale this one is affordable. The BT-1 does not have the Axial Tilt circuit but that is no problem if used with the Composer.

This unit had a malfunctioning phono pre-amp so the owner removed it creating a line level input for the phono. For some reason he also replaced the knobs. With those knobs installed It is starting to look more like a DIY project! Nice knobs similar to the originals can be found on Aliexpress or eBay.

If it was mine I would add extra RCA jacks on the back and replace the selector switch with one with more positions. Does anyone only have three stereo sources these days?

I'm tempted to buy it but I have absolutely no need for it. He had the starting bid at $150, now lowered to $99. With the phono board gone there is room enough for an Involve module!

https://www.ebay.com/itm/2661858994...cvAZP6xSZendcpjiKMRn78NeO/|tkp:Bk9SR9bEyvDiYQ

 

[Marcsten]

There is currently an auction on eBay for an Audionics BT-1 Preamplifier. Unlike the RS-1 Pre-Amplifier that also is for sale this one is affordable. The BT-1 does not have the Axial Tilt circuit but that is no problem if used with the Composer.

This unit had a malfunctioning phono pre-amp so the owner removed it creating a line level input for the phono. For some reason he also replaced the knobs. With those knobs installed It is starting to look more like a DIY project! Nice knobs similar to the originals can be found on Aliexpress or eBay.

If it was mine I would add extra RCA jacks on the back and replace the selector switch with one with more positions. Does anyone only have three stereo sources these days?

I'm tempted to buy it but I have absolutely no need for it. He had the starting bid at $150, now lowered to $99. With the phono board gone there is room enough for an Involve module!

https://www.ebay.com/itm/2661858994...cvAZP6xSZendcpjiKMRn78NeO/|tkp:Bk9SR9bEyvDiYQ

It's actually BT-2. Around 1980 when Steve Kennedy was working at Audionics, and I had scraped together the funds to purchase a Composer, I told Steve that I really needed a decent preamp and the ability to control the discrete 4 channels I used for CD-4 and Q-8. He built me a custom BT-2 with the stock phono board but bypassed the volume and balance. These controls instead worked the four discrete inputs and outputs he put on the back. So all in one, I had a great little pre-amp, the volume and balance for which was controlled by the Composer's controls, and a discrete 4 arrangement with volume and balance controlled by the BT-2.
It worked great and I used it for more than 15 years.
Ultimately, I found another way to control the 4 discrete in/outs and so only needed the pre-amp. I bought a small modern preamp called the Phenomena pre-amp. Although I always loved the BT-2, having a modern preamp was a revelation! The sense of openness and separation of the instruments was a stark improvement over the BT-2.
It sounds like this unit doesn't have the BT-2 phono preamp in it anyways, so is really just a box with funny knobs. I still have my custom BT-2 and it still works so far as I know.
Audionics really built that stuff back then!

 

[par4ken]

There is another BT-2 for sale on eBay. This time for only $125. It has a few problems though. The phono stage has low distorted output and the line stage outputs are unbalanced. It looks the the two boards are encased in a metal shield. I think that I read (perhaps the other for sale unit) that the boards are encased in epoxy, which would make repair difficult or impossible.

I have no need for another preamp but this unit looks so cool and matches the Composer exactly. Even if someone purchased it just for the case either replacing the boards with something else or use to make a passive preamp. Only three inputs plus tape (what were they thinking), I would replace the selector switch and add extra inputs!

https://www.ebay.ca/itm/16610144212...O2aj9nmxvncPYl4LORqHEIdYfW|tkp:Bk9SR5Csl-qQYg

 

[par4ken]

Yes I am a bit of an Audionics fan. I decided to to check eBay.com as sometimes items don't show up on eBay.ca if the seller is not offering international shipping. Anyway I discovered several Audionics preamps for sale. A couple of RS-1 Pre-Amplifiers in the $800 range. Also an Audionics of Oregon RS-2 Pre-Amplifier Perfect Working Condition excellent condition. Audionics of Oregon RS-2 Pre-Amplifier Perfect Working Condition excellent cond | eBayThat unit is interesting in that it is silver in colour. I assume that it is an earlier unit. I just wish that they would show "naked" pictures, I would like to see what is inside!