Eliminating RF Interference with the JVC 4DD-5

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berninahusq

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Hi guys,

As some of you have observed, my experience with CD-4 has been a rollercoaster ride. After I finally, successfully, calibrated my "working" 4DD-5, I noticed that it had a "Whirling Wind" background noise whenever I played a CD-4 record. I didn't think much of it then, since I was exhausted calibrating it, I thought I'd give CD-4 a rest.

In the meantime, I moved the working 4DD-5 next to a new computer setup to finally start digitizing some discrete albums. When I turned the unit on, the "Whirling Wind" was more pronounced, only when playing CD-4 records, however. The CD-4 radar light remained on at all times.

BUGGER....I thought....now I have TWO faulty 4DD-5s! Oddly enough, I thought even just recently having experienced CD-4 playback, it was never meant to be in my life.

After many days of playing around with it, I realized that I only got the "Whirling Wind" when both the 4DD-5 and the computer were ON (I always turned the 4DD-5 and computer on right after the other). Turning off the computer cleared up the background noise and the radar light only lit when I played a CD-4 record.

Whew! So, my question is, is there a way to shield this puppy from radio frequency interference? I use premium Monster Cable interconnects to and from my turnable/4DD-5/computer.

Thanks--Ed
 
I have the same problem with my T.V. and sound card- When I shut off the t.v. the noise is gone! But it's not recorded just on play back, so I moved the wires away and it goes away! I would like to get some shielded speaker wires!
Rob
 
Hello to all.

From a message by Greg Bogantz in the mailing list:

"So this brings up a caveat to anyone who would rebuild or redesign their demodulators: Be careful with the lead dress of the wires flying around inside the unit. I know from experience that what seems like an innocuous placement of wiring inside a demodulator can result in crosstalk at the supersonic carrier frequencies which will cause Type II distortion.

Maybe it's a matter of shielding those cables internally.
 
The 4DD5 is not shielded very well from outside interferences. This is due to the lack of local interference rich devices like computers and switching power supplies in the seventies. I have never shielded a 4DD5, but if I needed to, I would get some copper screen or sheet from a hobby store and glue it to the inside of the plastic parts of the case. connect these sheets to ground with soldered connections. An easier way would be to put the 4DD5 in a metal box and ground the box to the 4dd5's ground lug. Make sure the turntable is grounded properly as well. It could actually be the point of entry. It is just a matter of placing grounded metal between the source and the demod setup. You might also find it beneficial to ground the computer as much as possible, being wary of potential such as unshielded lan lines. Remember that radio waves bounce and reflect off metal surfaces like light striking a disco ball.

The Quadfather
 
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