Proper Adjustment of a CD-4 demodulator

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To The Prof: Thanks, you made my day! It's nice to know that my words have had such a positive effect, especially after it took me so long to get it right on my own setup. (I finally got it right about the mid 90's. it took me that long just to find a decent demodulator) I would recap the power supply, and the regulator circuits. Electrolytic capacitors do get weak on capacitance and get leaky over the years. When replacing capacitors, avoid ROHS if you can. They just don't hold up well. Using XLRs, Hmmm Interesting. Definitely better than DINs. The best XLRs are Switchcraft. They are silver plated, and they are incredibly reliable. Since working in the TV industry since 1984, I have seen only a handful fail, and they were really worn to the bone. They're so reliable that we routinely cut them off of old cables to reuse them. There's no risk. When I buy XLRs, I specify Switchcraft. I won't use any other brand. I have never thought of using FM lead. But I have often thought that oscilloscope probe wire would work great. But since the wires on my turntable were made for quad, there has been no need to replace them. Happy Listening!
 
I have a JVC cd-4 demodulator, when I play non quad albums, the red quad light goes on and off random, sometimes staying on for 30 seconds or longer. I'm guessing others have seen this too, what do you attribute it to?
 
Some have attributed it to random groove noise or wear that we can't hear. I feel the jury is still out. That is why I jumped on the strain gauge cartridge when it fell into my lap cheaply. I suspect that magnetic cartridges are too susceptible to stray interference, capacitance and muting switch issues. I have had no luck with magnetic cartridges, and I have bought four of them for CD4 and have at least 8 demodulators. I have tried changing wires, turntables, cartridges, needles and nothing worked. Right now my Technics demodulator with Strain gauge cartridge seems to work about 85% of the time in CD4 and plays stereo/mono discs just fine. Just to give you an idea about random noise, I played a 78 rpm disc that should have no frequencies recorded over 2 KhZ and the light went on and tried to decode with disastrous effect.
 
I didn't know if it was just something like the demodulator recognizing the stylus in use was quad...
 
No, it's not. Stereo records can include frequencies well above 15 kHz. Sometimes the frequency range is well extended above 20 kHz, which causes the demodulator to believe it has a quad record to decode.

Your demodulator may have a switch to set it to stereo playback only, in which cases the demodulator for the rear channel extraction being deactivated.

Everything above 15 kHz to 45 kHz is dedicated to the FM modulated information on CD-4 discs, with which the demodulator is able to reproduce four channel sound in combination with the unmodulated standard audio range (which is bandwith limited to 15 kHz) of the disc.

For stereo records switch your demodulator to stereo playback only.

-Kristian
 
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