Smell of Smoke

[The Quadfather]

While I was listening to a CD-4 record last night, I kept getting a whiff of burning semiconductors. I couldn't pin it down. However, it became obvious where the problem was when I switched my sound system for SQ encoding. When I dropped the needle, the sound was grossly distorted. My Audionics Space and Image Composer had fried. Today I will pull it out, and hopefully, it will be just a bad regulator or op amp instead of the Tate chips, made of unobtanium. If it's the worst case scenario, I guess I'll be looking at Involve's decoder. I bought my Audionics in 1979. My boss teased me about it being rubbed with snake oil because he had never seen an SQ decoder that really worked. I guess if it's dead, it had a good run. It burned a Tate chip once before, but Audionics was still around and was able to supply the unobtanium to fix it.

 

[The Quadfather]

It's out of the rack now, cover off, plugged in, no smoke, no burned smell, no black components. There was no mistaking the distorted sound and the smell last night. It could be the AX-7 that feeds it. How lucky would that be? Only one way to know, and that's to put it on the bench and run a signal through it. If it comes out clean, I'm a lucky quaddie.
The Quadfather

 

[The Quadfather]

Well, I got lucky. The Audionics unit survived. I still haven't figured out what was smoking, but it wasn't the S&IC. It turns out the input level got cranked up all the way, and it was over driven. When I switched it in, I assumed that it was the smoker when the sound was massively distorted.
The Quadfather

 

[surround.sound.enthusiast]

Whew! Breath of relief for you on the S&IC! Now the mystery is which piece of equipment is in trouble. . .

 

[Hamilton59]

“made of unobtanium”

Heh heh... I love it! What a great word!

 

[monarchee]

“made of unobtanium”

Heh heh... I love it! What a great word!

I reckon it's what dark matter is made of. You'll never see it on the periodic table but you can definitely see the evidence of it.

 

[LuvMyQuad]

Isn't Unobtanium what they were mining in Avatar ?

 

[The Quadfather]

There was actually something wrong with the Audionics unit. After I used it successfully one weekend with the covers off, and then I put the covers back on and racked it up, I waited till next weekend. When I fired it up to play the stereo material in my new Pink Floyd box set, I found the S&IC splattering again. A sad weekend of listening to early PF in mere stereo. Out of the rack it comes and off to the studio service shop. After careful examination I discovered that at one time I had replaced the screws for the bottom cover. Well the left channel input trace goes right under the screw hole, and the screw was touching the trace barely. A slight temperature change and it was shorting out. So, a search through the old screw bin for shorter screws, and I had the unit working just fine. And that Pink Floyd BBC material sounded great through it. You know, I'm really surprised the BBC did such a fine job recording this stuff. American TV at the time had the attitude that it was the picture that mattered, not the sound. Very little attention was paid to TV sound quality back then, and it was all monophonic. But then, I guess they were recording it for radio too, that would explain a lot. Anyway, the Audionics is in good shape now. Apparently, the unobtanium didn't leak out. I not only put in shorter screws, but I put in a piece of rubber to make sure no connection was possible. All better now.

 

[Jim the Oldbie]

Glad to hear your happy ending. Were you able to locate the part(s) that overheated?

 

[par4ken]

Shortly after reading this thread I pulled my S&IC out of the closet. Several years ago it started acting up, no front to back center separation. Over the years I had made several upgrades to it. I replaced the input volume and balance controls with "Black Beauty" pots. I replaced the electrolytic coupling capacitors with film types bypassed by Wonder Caps. I even changed a couple of the op-amps in the audio section TL074's replaced with AD713's. I would of done them all but as I recall they were rather expensive at the time and I think that I just screwed up and underestimated the quantity required. I later tried OPA4132's but the DES circuit was acting odd, I suspect those devices were oscillating causing the problem so I went back to the originals. Anyway I recently checked the IC's the TL074's in the DES input filters and the Interface circuit. One IC had a pin bent over and another one had one section that tested bad. The remaining 74's all tested good but the pins of all were very badly tarnished. I replaced them all with fresh chips. The unit is working now 90% at least, I had to turn the Cf-Cb adjustment pot all the way up to get the Cf led on the directional display to light, Cb lights up more often than it should. I'm getting good separation from the decoder though. I might have to change some of the IC sockets or try Deoxit on them, the directional display is fed from the interface circuit. As a brief audio test I swapped the unit with my QSD-1, immediately the silky smooth sound replaced the slight edginess of the QSD-1. I always said that the Audionics unit was very neutral sounding, everything else adds it's own coloration. Audionics added pull up resistors to the op-amp outputs to make them run in class A, that's why they require heat-sinks. SQ type stereo enhancement by this unit subjectively sounds as good as QS surround type enhancement, but QS surround is done in a more natural way, more about that in another thread. Once I find the baggie with the one missing knob and top cover screws for my unit I'll be able to put the unit back into service in my audio rack!

 

[Jim the Oldbie]

I always seem to have the opposite problem - that is, baggies containing bits that I can't remember what the hell they belong to.

If I come across one with a knob and some screws in it, I'll give you a holler.

 

[Sonik Wiz]

As a brief audio test I swapped the unit with my QSD-1, immediately the silky smooth sound replaced the slight edginess of the QSD-1

My own impression of the QSD-1 was that it sounded the slightest bit dull & muffled which I always put down to the enormous complexity of the 70's circuitry. At any rate I'm curious if you did any mods or upgrades to the QSD-1 as you did for the S&IC?

 

[par4ken]

My own impression of the QSD-1 was that it sounded the slightest bit dull & muffled which I always put down to the enormous complexity of the 70's circuitry. At any rate I'm curious if you did any mods or upgrades to the QSD-1 as you did for the S&IC?

Yes I did replace capacitors, at first just the power supply filter and some coupling capacitors, where there was room for film types. I removed the blend resistors as well. More recently I replaced most remaining electrolytic's with either film types or with Nichicon audio gold capacitors. During the last alignment I found that the mid band board wouldn't adjust properly and so replaced a couple of chips. At least the Vario-matrix chips are still plentiful on eBay and not unobtanium like the Tate chips! After the alignment I found the unit preformed much better than before. When I first purchased the unit some years ago I listened to it briefly (my S&IC was still functioning 100% at that time) I noticed an odd effect of hearing what sounded like the same instrument playing from more than one location, but with good separation, a result of tri-band processing I felt. After the repair and readjustment the unit preforms much better, I don't notice that abnormality anymore. I still have a philosophical almost a religious bias against multi band processing though, I think that it negatively effects the sound. Think about it, feeding the bass to one speaker and the treble to another would be a terrible way to synthesize stereo from mono IMHO.

 

[Sonik Wiz]

Quite interesting thanks for the reply.
Prtojects like this are,for me anyway, fun & often brings tangible sound improvement. At the very least it brings a sort of peace of mind; if something doesn't sound quite optimum you at least know what the problem isn't.

RE: Multi-band decoding. As Two Face might say in Batman, "I'm of two minds about this". In analog or digital the common practice is still to mix bass pretty much center front. And the highest frequencies are usually harmonics of lower fundamental tones:

For example the flute that we think of as a relatively high pitched instrument has the highest fundamental frequency shy of 3 kHz. Then anything higher than that is harmonic over tone that should be coming from the same direction, so why the need for high band decoding? The obvious exceptions on the chart above is the pipe organ & not shown of course a synth or midi keybaord can go as high or low as you want.

On the other hand with tri-band decoding if a lead guitar starts in left back & bass follows center front, both will keep their proper positions. Haha, I remember in olden days the train of thought was: Wow if the QSD-2 sounds that good just think how much more separation the QSD-1 will have! Of course it doesn't but it is a more stable soundfield image. And I'd say the biggest benefit of tri-band decoding is what you don't hear: artifacts. It is good to have different & appropriate filter time constants for each frequency range & this allows tri-band decoding to really operate in a special way.

I think the sweet spot in terms of complexity & benefit would be a dual band decoder set up. Reciognizing that most bass comes from upfront a simple non-enhanced decoder could be used for the bass section. This would allow bass positions to still be correct but with zero need for filtering to keep contriol voltage ripple & distortion down. And recognizing the higher harmonics should come from the same source position of the fundamental tone, the high pass section should handle that equally well.

 

[The Quadfather]

Actually, no. All I was able to determine was that it wasn't in the Audionics unit or the AX-7 mixer, which was just below the Audionics unit. Whatever it was, it quit smoking, and is finished burning up. There's a tuner and a cassette deck I never use. It could be either one of those.
The Quadfather

Glad to hear your happy ending. Were you able to locate the part(s) that overheated?

 

[The Quadfather]

Shortly after reading this thread I pulled my S&IC out of the closet. Several years ago it started acting up, no front to back center separation. Over the years I had made several upgrades to it. I replaced the input volume and balance controls with "Black Beauty" pots. I replaced the electrolytic coupling capacitors with film types bypassed by Wonder Caps. I even changed a couple of the op-amps in the audio section TL074's replaced with AD713's. I would of done them all but as I recall they were rather expensive at the time and I think that I just screwed up and underestimated the quantity required. I later tried OPA4132's but the DES circuit was acting odd, I suspect those devices were oscillating causing the problem so I went back to the originals. Anyway I recently checked the IC's the TL074's in the DES input filters and the Interface circuit. One IC had a pin bent over and another one had one section that tested bad. The remaining 74's all tested good but the pins of all were very badly tarnished. I replaced them all with fresh chips. The unit is working now 90% at least, I had to turn the Cf-Cb adjustment pot all the way up to get the Cf led on the directional display to light, Cb lights up more often than it should. I'm getting good separation from the decoder though. I might have to change some of the IC sockets or try Deoxit on them, the directional display is fed from the interface circuit. As a brief audio test I swapped the unit with my QSD-1, immediately the silky smooth sound replaced the slight edginess of the QSD-1. I always said that the Audionics unit was very neutral sounding, everything else adds it's own coloration. Audionics added pull up resistors to the op-amp outputs to make them run in class A, that's why they require heat-sinks. SQ type stereo enhancement by this unit subjectively sounds as good as QS surround type enhancement, but QS surround is done in a more natural way, more about that in another thread. Once I find the baggie with the one missing knob and top cover screws for my unit I'll be able to put the unit back into service in my audio rack!

Hey Par4ken:
Did you buy your Audionics S&IC brand new when they came out, or did you pick it up on Ebay or something like that. There weren't that many made. It's good to hear that one has been returned to service. I have heard of a few of them burning up over the years. What a shame. Mine died a couple of years after I bought it, and I had to repair it myself. I was dirt poor (I bought the S&IC before I got married) and couldn't afford to send it off and have the upgrade chips installed. So, Audionics sent me the replacement for the bad chip, and instructions on how to modify the power supply to get a couple more volts from it. So I have what is probably the only hybrid of the old chips and the newer chips. It worked though. Up till recently, it's worked ever since. It's a good idea to change the IC sockets if you have the skill to do it. Just don't break the pins on those unobtanium chips. I once had a flawless Billy Joel record I loaned to another quaddie to copy. He decoded it and copied it using a Fosgate tate unit. He sent back a copy DTS CD with the original record. I listened to it, and it sounded pretty good, but I have to say, I still like the S&IC better. Hopefully, it'll hang with me for the rest of my days.

 

[par4ken]

Hey Par4ken:
Did you buy your Audionics S&IC brand new when they came out, or did you pick it up on Ebay or something like that. There weren't that many made. It's good to hear that one has been returned to service. I have heard of a few of them burning up over the years. What a shame. Mine died a couple of years after I bought it, and I had to repair it myself. I was dirt poor (I bought the S&IC before I got married) and couldn't afford to send it off and have the upgrade chips installed. So, Audionics sent me the replacement for the bad chip, and instructions on how to modify the power supply to get a couple more volts from it. So I have what is probably the only hybrid of the old chips and the newer chips. It worked though. Up till recently, it's worked ever since. It's a good idea to change the IC sockets if you have the skill to do it. Just don't break the pins on those unobtanium chips. I once had a flawless Billy Joel record I loaned to another quaddie to copy. He decoded it and copied it using a Fosgate tate unit. He sent back a copy DTS CD with the original record. I listened to it, and it sounded pretty good, but I have to say, I still like the S&IC better. Hopefully, it'll hang with me for the rest of my days.

I purchased the S&IC used from Michael Robin. I believe that he was selling it for someone else, he considered keeping it for himself but was still very satisfied with his Lafayette SQ-W. He did want to know both my initial impression and my impression of it after I had listened to it awhile. I had previously tried to purchase one from Audionic's Canadian distributor. I was told that because there was no dealer in my area I could buy direct from them and so sent a certified cheque to reserve/purchase my unit. I was told that there was a delay as the Canadian model would require a heavier power transformer to qualify for CSA approval. Latter my cheque was returned, they couldn't supply the unit and apparently never did import any. Coincidentally a friend that I used to work with purchased a used one as well, sometime after I did. Recently I ran into another fellow who had gotten that unit from my friend, it apparently needs a power transformer! If I run into him again I'll see how he made out or maybe even purchase it off of him. I have a Pace desoldering station so changing sockets isn't that gig a deal but will likely poke around a bit more to see that is going on with the Interface, things point to IC U7, not much there to go bad just the socket.

 

[par4ken]

Well I replaced the socket in the Interface circuit to no avail. After more detective work I see that the input to the Interface comes from the LM1852 (RA402) unobtanium chip. That chip while still producing outputs for center front and back, they aren't quite right. All I can do at this point is set the Cf-Cb pot all the way up, it still was sounding good during my brief listening test.

 

[The Quadfather]

Well, in the end I lost it. The Audionics unit kept acting intermittent, and it would work for awhile, then it would quit. I would put it on the bench and it would be working. this happened several times. Finally it just quit, and I was able to actually dig into it and find what was really wrong. Unfortunately, it was one of the Tate DES chips. There are two in the unit, one handles the front channels, and the other handles the back. When the bad chip was in it's socket, it killed all four channels. Pull it out, and the two rear channels start working. If anybody has a burned up Space and Image Composer they want to let go cheap, I'd be interested. All I need is one of the two chips. Otherwise, I guess I'll be ordering an Involve SQ unit.

 

[par4ken]

Sad news indeed. I too though my unit was working at least acceptably if not quite right, but when I tried it again the sound was low and noisy. I checked it with the scope and it looks like something is again causing a stability problem. Two units for sale on eBay, but high prices and both are being sold as is untested! Involve is an option, I do have the SQ and the Involve evaluation modules, but still love the sound of the Tate.