Noise

8thnerve · « **on:** 15 Oct 2003, 11:31 pm »

There is a very strange thing happening and I am wondering if someone can shed any light on it. I am getting a buzzing sound coming from my speakers when both of the RCA inputs are plugged in. When one of them is out, either one, the buzzing stops, in both channels. I have tried changing the preamp, the cables, and it seems to be related to the amp inputs. What could cause this?

tkp · « **Reply #1 on:** 15 Oct 2003, 11:51 pm »

You need to tell us your system setup.

There was a case where two mono block amps that plug into two AC outlets which was a bit far from each other. The system would buzz if both RCAs are connected to the preamp because the preamp connecting the ground of the left and right channel together. With both amp plug-in a ground loop is formed between the AC outlets and the amps via the preamp ground connection.

warnerwh · « **Reply #2 on:** 15 Oct 2003, 11:59 pm »

Is this like a 60hz buzz and is the volume the same no matter where the volume control is? It sounds like a possible difference in the ground of your amp and preamp. Try lifting the ground on the preamp.

ton1313 · « **Reply #3 on:** 16 Oct 2003, 01:11 am »

What do you do if your Pre is un-grounded?, only two prongs?

tkp · « **Reply #4 on:** 16 Oct 2003, 01:20 am »

Quote from: ton1313

What do you do if your Pre is un-grounded?, only two prongs?

If your preamp only have two prong then there is no ground loop because your amp would ground the system (assuming the source is also two prong). In the case of mono block amps, both amp should plug into the same AC outlet to avoid the ground loop.

8thnerve · « **Reply #5 on:** 16 Oct 2003, 03:29 pm »

It was in fact the preamp's ground. When lifted, the noise disappears. I had not even considered this since all the equipment is plugged into a power conditioner in separate banks. Now I'll have to make a power cord with no ground so I don't have to go through a cheater plug...

Thank all of you for your help.

john curl · « **Reply #6 on:** 16 Oct 2003, 10:16 pm »

Grounding is not my best subject, BUT whatever works is really important. I have found this same problem, over the years. One thing that we have found, and this has been known for many decades, that reversing the AC plug can lower leakage on the external case. Sometimes, we can find something like 100V AC on the metal case! This seems to come from how they build the power transformers. It is safe from you being electrocuted, because the current is tiny, but it can cause hum.

avahifi · « **Reply #7 on:** 18 Oct 2003, 11:59 pm »

Actually the most common cause on hum is because they don't know the words.

Frank Van Alstine