how do I troubleshoot a ground-loop?

[heatz1express]

I hooked up some speakers and an amp this spring, using the radio that was in my boat. The amp is a Sony xplode amp and the speakers are all made by Koss. Since I had six speakers but the amp only had outputs for four I hooked the 6x9's up to the rear outputs in-phase and the four 2-way speakers to the front outputs in-series as per manufacturers instructions. I would have hooked them all up in-phase but the warnings changed my mind.<br /> The problem I have now is that with the boat running there is an annoying hum that coincides with rpm.s Hooking power supply for amp directly to battery and installing noise suppressor makes no diff. with engine off-sounds great. I was told that I have a ground-loop... so now what?

 

[datawire]

Re: how do I troubleshoot a ground-loop?

Try hooking up the receiver to the down-stream side of your noise suppressor, as well as the amp. The amp doesn't know the difference between hum/noise and music - it amplifies everything. A ground loop is when you have multiple paths to an earth ground, each with minute differences in resistance. Major problem for computers and big RF gear - not even applicable in your case. I suspect whoever told you that was your problem simply heard the term somewhere. You don't even have a "ground" - you have a return path to the power supply (battery).

 

[SingleShot]

Re: how do I troubleshoot a ground-loop?

You are going to need a galvonic Isolator or Audio Isolator to help fix this. Radio shack sells them. <br /><br />You connect the isolator between the amp input and reciever output. The problem is impedance mismatch and the fact your motor is inducing noise. As the previous post indicates. <br /><br />The Isolator will decouple the audio line connections between the amp and reciever yet pass the signal. Any line filters you put in on the dc supply should be as close to the source as possible. As the previous post suggested move the amp and reciever connections after the filter and make the power connections for each as close as possible to one another. Connect the negative leads of the amp and reciever as short as possible between them, then connect the main negative lead to those to form a star connection. Do this for the Pos connection as well. This will keep the resistance of the negative "power" lead between the Reciever and amp as low as possible, you can use big wire here as this will also lower the resistance. Since most electronic audio gear uses the negative as the ground some do not fully isolate this from the power and ground loops "Bad return paths" can be formed. I work in the electronic controls field and noise is an animal with out rules. <br /><br />Then put in the audio isolator between the reciever output and amp input. I'm assuming you are connecting them at line level "rca jack connections between the reciever and amp" which can make matters worse for noise. If your equipment has the ability to connect signal level that would be the way to go. Keep thos leads short is possible also. You may want to look into shielded cables also.<br /><br />Good Luck<br /><br />JK