JVC 4DD-5 Demodulator

[jshort74]

I just puchased a JVC 4DD-5 Demodulator on ebay and I am having some troble with it. I connected my turntable to the two phono inputs and the 4 outputs from the demodulator to the four aux. inputs on my Pioneer QX-8000. Wehn I turn on the demodulator all I get is a buzz through the speakers. Do I have this thing connected properly? Does anyone have any idea what is wrong. I have a pretty good idea that I just purchased a paperweight.

Thank you

 

[Cai Campbell]

Does it buzz when your turntable is not connected to the phono inputs?

 

[jshort74]

I have not tried that yet, Iwill. However, the turntable works fine when it is connected to my modern reciever.

 

[Quadwreck]

It seems to me that your turntable's ground cable isn't connected.

 

[Cai Campbell]

Yeah... that's where I was headed...

 

[jshort74]

Can you tell me how to connect my ground cable. Do you mean a third prong on the plug? I know there is a place to connect a ground on the back of the demodulator. You'll have to excuse me I am new to vintage audio equipment.

 

[quadjoe]

Hi I also own a 4DD-5 demodulator.

On the right side of the back of the unit, just above the power cord you will find a grounding connector that when you push on it exposes a hole in the shaft of the connector. You need to run the ground wire from your turntable (not the ground on the electric plug, but a separate wire that usually is attached to the turntable near the audio cables) to the grounding connector (just pass the wire through the hole). This may eliminate the hum. If it does not you will have to have the unit repaired. Hope this helps.

 

[Cai Campbell]

What he said...

 

[jshort74]

I did try disconnecting the turntable from the inputs on the demodulator and it still had the buzz. I quickly looked for a ground wire off of the back of my turntable and I didn't see one. I'll try to find one or some place to connect one. If I cannot find one, couldn't I connect a wire to the frame of the turntable and then connect that to the ground connection on the demodulator? There are ground connections on the back of my reciever.

 

[Cai Campbell]

If the unit buzzes without your turntable connected to it, then there is most likely a problem with the demodulator. The problem could also lie with the inputs on your receiver. Does your receiver buzz if you disconnect the demodulator? Try one channel at a time. If the buzzing goes away from each channel as you disconnect the demodulator from the receiver, then the problem is with the demodulator. If the buzzing does not go away, then the problem is with your receiver.

 

[jshort74]

I can turn the demodulator off and the buzzing goes away. Turn it back on and it is still there. I have also tried to use the other aux. channel, so I guess the demodulator is bad. If anyone has any more suggestion they will be appreciated. Thank you to everyone who has been helping me out.

 

[The Quadfather]

I can supply you with a service manual for your JVC 4DD5. Email me at [email protected] and I can help you. I have that demod and it is a fine one. Well worth the bother . Wait a few days for reply.

The Quadfather

 

[quadjoe]

I have a hunch about something. Let me ask you this:
What kind of turntable and cartridge are you using? As far as I know any turntable equipped to work with a magnetic cartridge has a ground wire. Waaaay back in the early '70's I owned a (everyone please pardon me) BSR turntable equipped with a ceramic cartridge and it did not have a ground wire. When I upgraded it to a magnetic cartridge I had to run a wire from the chassis of the turntable to the grounding post on my receiver to eliminate the hum. One thing to keep in mind is that a ceramic cartridge produces way too much voltage for a magnetic phono stage and it will produce a hell of a buzz if you hook it up (and could possibly damage your phono section or demodulator). Finally, Panasonic produced semi-conductor cartridges for CD-4 which required a special phono stage and would be incompatible with the 4DD-5 (I have one of those Panasonic receivers which requires this type of cartridge, but I'm not using it because I can't find the right cartridge and I'm too cheap to pay someone to modify the phono stage for me :-( ).

 

[sspsandy]

I had this problem with my JVC 4DD5, it turned out to be the switch in back for 2/4 channel mode. I sprayed it with some tuner spray, worked the switch back and forth a bunch, and it fixed the problem.

 

[quadjoe]

Sandy,

I recently had a similar problem with my 4DD-5 demodulator, and you are right, tuner spray on the 2/4 channel switch solved the problem. Obviously, these units don't like dirt in their switches! Thanks for the post!

Quadjoe