Just the facts:
-1989 S10 Blazer, 4.3L V6 with standard alternator
-all battery cables have been upgraded with 2-gauge welding cable. Crimped, silver-soldered, heatshrunk.
-HU: older AIWA CDMP3 job. Only has 2 RCAs on the back. These have been jumpered via several "Y" cables to 3 RCAs - 2 for 4-channel seperates amp, 1 for mono sub amp.
(I dislike using Y-cables, but when you have to, you have to.
-All RCA are run to the HU, and run down the center of the vehicle- more than 18" away from power.
-Seperates Amp: MTX TD75.4. Brand new, from Crutchfield on Friday. Installed today.
-Power supply: 2-GA from the battery, through firewall, grommets and fuses in the obvious places. This lead goes to the rear of truck via driver's side near door. At
the amp, a 18" stinger of 8-GA is soldered to the 2-GA to go supply the amp. 30A fuse on this lead. Soldered on a bifurcated terminal for the amp connection.
-Ground: used the supplied 4-GA lead. Soldered on a bifurcated terminal for the amp connection. Soldered on a large-gauge ring terminal to the other end. As instructed
in the install guide, I drilled a hole in the body (floorboard), sanded to bare metal, and through-bolted. I went one better, using 3/8-16 stainless bolt and nyloc,
and using electrician's grease (Eezox? Can't recall the name- it's made for this task).
Problem: Electrical noise with volume at "0" on the HU:
-key in accessory, engine off (duh, and/or hola?): no noise, "0-bits" noise floor. The goal for all installs.
-key in "run", engine not running: electrical noise. Obviously coupled from the running electrical system, not sure what circuit. Hard to describe it- obviously not
alternator whine, more along the sound one might hear from a flourescent bulb with a bad ballast
-key in "run", engine running: classic, monstrous alternator whine.
I bought a couple of GLIs from Radio Shack for a "quick fix". They help but don't fix the problem. When I was testing the noise, I noticed that if I remove the white
(left?) RCAs at the amp, as soon as the shield breaks contact, noise is gone- each channel carries some of the noise. If I remove both, the noise is completely gone.
Haven't gotten to adjusting the gains yet, but the noise is there with the gains all the way down.
Possible issue: I think the issue might be the 3 y cables at the HU. I need to test around that, but it's too late tonight. If this ends up being the issue I will
replace the HU, as I am not married to it, it's 15+ years old, time for replacement anyway. I saw a Power Acoustix brand (may be mis-remembering) at Pep Boys for $100,
with a DVD display. Yes, I know it's not up to competition vehicle use, or good enough to be put in your car. I don't care- this is a working/married man's truck,
being built for mild expedition use and DD, kept inexpensive while keeping my hacker side busy when not at work. I have plans, but not thousands of dollars to waste on
this like I did my car when I was 20...
Also, might be that I need to run the ground to the battery. Along that line- have a 2-ga welding cable built to run from the grounding point of the amp (other side of
the body, under the 3/8 bolt I installed today) to the ground terminal of the battery.
Possible issue, but I dout it: I have heavy-gauge (2/0) disconnects for the battery fore and aft. These are for winch and jump-start use. There's a very remote chance
they might be acting as an "antenna" to couple noise in, but I REALLY doubt it as they'd likely be damped by the battery.
Likewise, I have the sub-amp RCA flaked out to the rear of the truck awaiting arrival/install of the sub amp... but I have the terminals insulated with electrical
tape, highly doubtful this is the issue either)..
Thougts?
"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"