As the end of April coming closer I am in sweet anticipation of receiving the new Surround Master v2 soon thereafter. It is bitter sweet because having the SM v2 will certainly become my primary go to decoder for stereo & encoded material. It will reduce almost to zero any urgency to fix my Tate 101A or my Sansui QSD-1000. I expect the SM v2 to excel in performance over these units.
So this has got me on a nostalgic binge of digging out various old decoders & appreciating them all one more time. My Electro Voice EVX-4 (which sounds a lot better than one would expect) and the Heathkit AD-2002 ( the new improved EV decoder that doesn’t sound as good on stereo) and the Fosgate Model 5 that just sounds so bland.
Also in my Closet of Quad is a Fosgate Audionics DSM 3606. DSM of course stands for Digital Space Matrix & also there is a Pro Plus tacked on at the end. If they used smaller type on the front panel maybe they could work in some more modifying superlatives such as Platinum or Mega. You can take a look at an ad for the 3602 here from Disclord’s archive:
DSM 3602
And while you’re looking at that page, who can find the embarrassing typo?
There were a total of 6 DSM models: 3600, 3601, 3602, 3604 3608, 3610. All had different combinations of wired/wireless remote, with/without rear channel power amps, with/without Dolby approved time delay on the back channels. There was also the Gavotte original, Mark II, and the RFQ 5000 that sported the DSM label. These were all intended for use in cars & not otherwise pertinent to this note. There are plenty of other notes on these models just search the forum.
Elsewhere Wagonmaster_91 made a good post about his DSM 3608 decoder & worth a read:
DSM 3608
You can see some good shots of the insides that is very close to mine before I started modifying it. Also in that post he made an astute observation:
I’d carry that a step further & say that the entire DSM line suffers from middle child syndrome. It came right after the Fosgate Tate 101A that everybody compared it to & was somewhat disappointed. It came before the Model 3, 4, 5 etc that dropped the DSM label for digital servo logic surround processor. After that the Fosgate Audionics name disappeared, absorbed into the Land of Harman Kardon where the Shadows lie.
At any rate when I saw an affordable DSM 3606 pop up on EBay at least 10 years ago I snapped it up. I mean a collaborative design between Fosgate & Scheiber? Man, how great can that be?
Before I auditioned it I took the top lid off to inspect inside. Yes this was a used product so no worries about warranties. Actually that’s the first thing I do with new equipment as well (here’s looking at you SM v2). I void factory warranties faster than I can void my bladder.
I was disappointed when I found 2 large modules containing the directional control voltage generator and the actual matrix circuitry. I studied the PCB & circuitry a bit, put the cover back on & gave it a listen.
It just was the weirdest sounding decoder I ever heard. Pushing the mode buttons had an audible effect but nothing that really sounded clear, or what you expect from the function names. I tried stereo, SQ, QS. It certainly gave outputs from all speakers, center front was pretty much up front and ambience in the rear but everything else seemed wrong. I pulled it out of my system & went back to tinkering on it.
Eventually I removed the bottom panel & saw those modules had something like 12 pins on two sides soldered in. So what the heck, I pulled out my solder wick & started removing them. Successfully done I was again disappointed to see they were potted in RTV type silicone rubber! I couldn’t turn back now. I did some research and found a Loctite product called Chisel that would remove cured silicone rubber. It doesn’t really dissolve it away but it makes it goopy so you can clean it out with a Q tip or compressed air. Lather, rinse, repeat.
It took a while but studying the Control Voltage Generator module I realized it was almost exact as an example circuit in a Scheiber patent. Right down to individual component values. This was designed to look at front/back individually and left/right as a single varying polarity control signal. The matrix module I don’t remember so much about except there were some regular DIP Op Amps with the pins spread out & soldered so it was pseudo-surface mount. A hand full of transistors, a lot of resistors. I couldn’t match it to any circuitry I’d seen before.
I replaced the modules & re-soldered them. I also made some circuit mods such as improving a few capacitors & upgrading the numerous TL074 op amps to AD 0110. The rear channel output transistors ran hot even with no loads hooked up so I removed them. When I was done it looked like this:
Yes some of those ugly caps you see are my mods but sometimes electricity doesn’t care how pretty it looks. So I hooked it all up again,& again was underwhelmed by the decoding. The sound was crisp & clean, no artifacts but it sure didn’t fill my needs. I pulled it out my system & it found a long term home in my Closet of Quad. In fairness to the unit I did not do any alignment or tune up since I didn’t have instructions to do so. A few weeks ago I said what the heck what harm can I do? Why not try? So I did.
More to follow.
Any further info or corrections are most welcome.
So this has got me on a nostalgic binge of digging out various old decoders & appreciating them all one more time. My Electro Voice EVX-4 (which sounds a lot better than one would expect) and the Heathkit AD-2002 ( the new improved EV decoder that doesn’t sound as good on stereo) and the Fosgate Model 5 that just sounds so bland.
Also in my Closet of Quad is a Fosgate Audionics DSM 3606. DSM of course stands for Digital Space Matrix & also there is a Pro Plus tacked on at the end. If they used smaller type on the front panel maybe they could work in some more modifying superlatives such as Platinum or Mega. You can take a look at an ad for the 3602 here from Disclord’s archive:
DSM 3602
And while you’re looking at that page, who can find the embarrassing typo?
There were a total of 6 DSM models: 3600, 3601, 3602, 3604 3608, 3610. All had different combinations of wired/wireless remote, with/without rear channel power amps, with/without Dolby approved time delay on the back channels. There was also the Gavotte original, Mark II, and the RFQ 5000 that sported the DSM label. These were all intended for use in cars & not otherwise pertinent to this note. There are plenty of other notes on these models just search the forum.
Elsewhere Wagonmaster_91 made a good post about his DSM 3608 decoder & worth a read:
DSM 3608
You can see some good shots of the insides that is very close to mine before I started modifying it. Also in that post he made an astute observation:
The 3608 suffers the "middle child" syndrome in the 3600 series of 360 Space Matrix surround processors.
I’d carry that a step further & say that the entire DSM line suffers from middle child syndrome. It came right after the Fosgate Tate 101A that everybody compared it to & was somewhat disappointed. It came before the Model 3, 4, 5 etc that dropped the DSM label for digital servo logic surround processor. After that the Fosgate Audionics name disappeared, absorbed into the Land of Harman Kardon where the Shadows lie.
At any rate when I saw an affordable DSM 3606 pop up on EBay at least 10 years ago I snapped it up. I mean a collaborative design between Fosgate & Scheiber? Man, how great can that be?
Before I auditioned it I took the top lid off to inspect inside. Yes this was a used product so no worries about warranties. Actually that’s the first thing I do with new equipment as well (here’s looking at you SM v2). I void factory warranties faster than I can void my bladder.
I was disappointed when I found 2 large modules containing the directional control voltage generator and the actual matrix circuitry. I studied the PCB & circuitry a bit, put the cover back on & gave it a listen.
It just was the weirdest sounding decoder I ever heard. Pushing the mode buttons had an audible effect but nothing that really sounded clear, or what you expect from the function names. I tried stereo, SQ, QS. It certainly gave outputs from all speakers, center front was pretty much up front and ambience in the rear but everything else seemed wrong. I pulled it out of my system & went back to tinkering on it.
Eventually I removed the bottom panel & saw those modules had something like 12 pins on two sides soldered in. So what the heck, I pulled out my solder wick & started removing them. Successfully done I was again disappointed to see they were potted in RTV type silicone rubber! I couldn’t turn back now. I did some research and found a Loctite product called Chisel that would remove cured silicone rubber. It doesn’t really dissolve it away but it makes it goopy so you can clean it out with a Q tip or compressed air. Lather, rinse, repeat.
It took a while but studying the Control Voltage Generator module I realized it was almost exact as an example circuit in a Scheiber patent. Right down to individual component values. This was designed to look at front/back individually and left/right as a single varying polarity control signal. The matrix module I don’t remember so much about except there were some regular DIP Op Amps with the pins spread out & soldered so it was pseudo-surface mount. A hand full of transistors, a lot of resistors. I couldn’t match it to any circuitry I’d seen before.
I replaced the modules & re-soldered them. I also made some circuit mods such as improving a few capacitors & upgrading the numerous TL074 op amps to AD 0110. The rear channel output transistors ran hot even with no loads hooked up so I removed them. When I was done it looked like this:
Yes some of those ugly caps you see are my mods but sometimes electricity doesn’t care how pretty it looks. So I hooked it all up again,& again was underwhelmed by the decoding. The sound was crisp & clean, no artifacts but it sure didn’t fill my needs. I pulled it out my system & it found a long term home in my Closet of Quad. In fairness to the unit I did not do any alignment or tune up since I didn’t have instructions to do so. A few weeks ago I said what the heck what harm can I do? Why not try? So I did.
More to follow.
Any further info or corrections are most welcome.
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