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-   -   earthing rca shields... (http://www.diyaudio.com/forums/car-audio/153350-earthing-rca-shields.html)

marko 14th October 2009 04:31 PM

earthing rca shields...
 
got an amp here (trying to get my junk stash down :o) and it only has output if i earth the rca shields to the heatsink, now i'm guessing this is not ideal and in a car would pick up some pretty bad noises! what would cause this issue? i traced the rca shield all way back to board and is fine, what happens after this is a mystery.

amp is an old philips dap600 (think alpine 3552s ;))

Perry Babin 14th October 2009 06:00 PM

Are you using an ipod for the signal source?

marko 14th October 2009 06:09 PM

no, proper headunit on it's own power supply though..

Perry Babin 14th October 2009 06:15 PM

If you don't have ~0 ohms between the ground terminals of the two supplies, connect them together with a jumper wire. Then confirm that you have ~0 ohms between the shield of the head unit (RCAs not plugged into the amp) and the ground terminal of the amp (amp connected to the power supply).

Remove the ground to the heatsink that you installed and see if the amp works normally.

Ipods cause more problems (due to a lack of a common ground) than any other signal source, that's why I suspected that you were using one.

TO-3 14th October 2009 06:20 PM

Quote:

Originally Posted by marko (Post 1949946)
got an amp here (trying to get my junk stash down :o) and it only has output if i earth the rca shields to the heatsink, now i'm guessing this is not ideal and in a car would pick up some pretty bad noises! what would cause this issue? i traced the rca shield all way back to board and is fine, what happens after this is a mystery.

amp is an old philips dap600 (think alpine 3552s ;))

Most likely that the ground-path is missing to the RCA shield. If you open your amplifier and look close to the RCA connectors, there should be a resistor that goes from the RCA shield to EARTH or even a separate audio ground, on each channel.
If you have a meter, measure the resistance between RCA ground and EARTH ground. The resistance can be in a range from 10 ohms up to a couple hundred ohms. I suspect that your resistors may be open.
Can you post a pic of the input stage of your amp?

Jon

jol50 14th October 2009 06:55 PM

In case that does not work out, make sure you hook it all up like Perry said. I had an old amp that would not work without RCA connected they grounded the input section. If an alpine I doubt it would be that way, should have something connected to the RCA shield and eventually to ground inside the amp.

marko 15th October 2009 04:36 PM

ok, took a picture of the preamp board.. also there is no resistance at all between the rca shield and earth terminal.

http://i5.photobucket.com/albums/y17...5102009595.jpg

Perry Babin 15th October 2009 05:18 PM

Can you post a photo of the circuit board on the other end of the amp?

TO-3 15th October 2009 05:48 PM

Well, it looks like the two large resistors, in the lower right corner of the daughter board are intact. You can measure across them to verify, but I would suspect that the ground is not even connected to the DB. You may have an open trace on the bottom of the main board, or one of the wires, that connects to the board, may be open, or have a poor contact on a connector.

Let us know.

Jon

marko 15th October 2009 06:02 PM

the white/blue connectors that carry signal seam to loose earth continuity (thin black wires inside brown cables) from the daughter board there on to the main board, those big resisitors do seam to be fine.


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