View Full Version : Ground loop isolators killing low frequencies

garys 68
09-11-2011, 07:15 AM
I've had an alternator whine in my separate power amp since I installed it. It's a 2 channel amp, running 6 x 9s on one channel and subs on the other.
I have strung temporary ground wires everwhere. Finally I put in a ground loop isolator between the head and amp. It got rid of my alternator whine but killed the low end frequencies at the amp.
Any suggestions on where I screwed up or what to try next?

09-11-2011, 08:25 AM
To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other.
Simplify your wiring. Single common points of + - connectivity.

garys 68
09-16-2011, 04:21 AM
The amp was well grounded but it looks like the head unit screwed to the dash was the weak point. I pulled a 12 g ground for the head unit from the amp. But there's still an audible whine, although much quieter. Maybe the head unit grounding itself to the dash?
Is there a good ground loop isolator out there that doesn't kill the low end frequencies?

09-16-2011, 06:33 AM
Not sure if this helps you or not but a long time ago had the same thing and a friend who's been in the stereo business a long time told me to just disconnect the ground wire to the head unit. I thought it wouldn't power up but he said it would ground through the shield on the antenna wire, he was right and ALL the noise went away.

garys 68
09-16-2011, 02:36 PM
Actually the head unit is probably grounded through the dash and antenna/fender. I tried disconnecting the antenna, no difference. The quietest setup was grounding the head unit to the point where the amp was grounded. Not sure if it's possible to isolate the head unit from the dash.

12-05-2011, 03:40 AM
Also dont forget to to install a good condenser on the battery output on the alternator. Any good condenser with a lead on it, bolt case boy to block or alternator case or bracket and solder a ring terminal and some wire to the lead out of it. If its still there you might actually be hearing ignition noise and a second condenser on that might help or replace one inside dist if you are using HEI.

01-05-2012, 07:44 AM
Does the whine go away when the amp is powered up and the RCAs disconnected at the amp?
Is the noise there when the RCAs are connected to the amp but disconnected from the head unit?
Have you tried to ground the RCA shell directly to the deck yet?
Have you tried grounding the RCA shell at the amp to the chassis?
Is your amplifier power wire hooked to the alternator charge post instead of battery B+ terminal by chance? (don't use the alt charge post)

I am assuming you have run all RCA interconnects away from power wires and made sure the alt bracket and engine have good grounding to the body and frame. One quick way to see if the RCA's are picking up noise is by running a high quality set of RCA's outside the car away from any other wiring. If the noise goes away, reroute the interconnects or even replace them with a "twisted pair" type.

From my experience as a former stereo shop owner (for better or worse):
Grounding everything to one point is a good troubleshooting technique to find weak grounds, but the best ground is the shortest ground wire straight to the chassis/body. Grounding everything to one point can cause ground loops as easily as it can improve them. If it improves the noise problem you still have to deal with the root cause. If someone else installed the deck make sure the head units B+ filtering is still in place.

I know this seems like stupid stuff, but I throw it all out there just in case you missed something simple. If all of this fails there is a chance the power supply filtering in the amp isn't up to the job for whatever reason(rare). You will find that by borrowing a different amp just to see if the problem still exists with the different amp