cd-cassette combo noise question

I have a 2000 Sonata which came with the standard am-fm-cassette player. I
bought a used cd-cassette combo from another 2000 Sonata and had it
installed. The sound level was inaudible so I had it removed. I was told
in this newsgroup that the combo required a four-channel amplifier. I
bought a brand new (almost "no-name" brand) amplifier 100x4 on Ebay. It sat
around my house for a long time until I found someone to do the install.

Today, I had it installed and I am very disappointed. Although the combo
works great, there is a very high pitched hum (almost a ringing sound) when
the engine is running. When the engine is NOT running, it is not there.
The installer says it is because the amplifier is junk and I need to buy a
new one, preferably a well-known name brand. Is this correct? What is
REALLY causing this noise? Is there another, less expensive option besides
buying a name brand amp? Will a noise filter work?
Any thoughts would help.

Thanks,
Joe

 

==========
Joe,

The installer in *wrong*. I was running a *very* inexpensive 4-channel
amp with the same model head unit you have and it ran great.

However -- first I made the mistake of having it "professionally"
installed by the local stereo shop with the best reputation. It had a
bad hum, and I was told the same thing you were -- of course, they are
insufferable snobs and maintain that anything they don't sell is junk.

After three trips back there I took out their installation completely
and re-ran all the wiring. After that didn't completely fix the problem
I finally checked the gain controls (they control the strength of the
input signal) and reset them to completely eliminate the hum -- the
installers had them turned up so high that it was overloading the amp.

There are other things to check, however, that could also produce the hum.

First, it is essential that the amp be well grounded, and that there be
no eddy current (or "ground loop") between the head unit and the amp.
The only way to be 100% assured that you don't have a ground problem is
to run a heavy gauge ground directly from the battery.

Second, the hot wire for the amp should be shielded with a metal shield
that is itself grounded to the battery. The hot wire should also be
really heavy gauge -- it can't be too big. The shielding of the hot
wire is important because the computer modules in the car "broadcast"
enough electrical noise to introduce signal distortions into the input
current (and there is no practical way to run the wires far enough away
from all those source).

Finally, use really high quality RCA cables from the head unit to the
amp -- poorly shielded RCAs will pick up a lot of noise.

If the installation is problem free you do not need a noise filter --
those can cause more problems than they solve.

Good luck with the troubleshooting, but be assured that it is 99%
certain that it is *not* your amp.

Harry

 

If the noise goes away when the engine is turned off then it is almost
certainly a grounding problem.