[johnmatrix]

One of the problems of upgrading is the better equipment reveals flaws in your system. When I switched the O2, I noticed a slight hum at a very low frequency and level. It disappears when I touch the interconnects or output jacks but not the cases. For my KGSS, I have grounded everything to the power supply with a ground loop buster circuit going to the chassis. My source is grounded to earth ground with a group loop buster to the chassis and the output jacks are tied to the chassis by a metal plate. Any input you guys could offer would be appreciated.

 

[Pars]

Quote:

Originally Posted by johnmatrix /img/forum/go_quote.gif One of the problems of upgrading is the better equipment reveals flaws in your system. When I switched the O2, I noticed a slight hum at a very low frequency and level. It disappears when I touch the interconnects or output jacks but not the cases. For my KGSS, I have grounded everything to the power supply with a ground loop buster circuit going to the chassis. My source is grounded to earth ground with a group loop buster to the chassis and the output jacks are tied to the chassis by a metal plate. Any input you guys could offer would be appreciated.

Since the output jacks are grounded to the circuit ground (I presume) thru the - connections, are you sure you also want to ground the jacks to the case, given the presence of the ground loop breaker?

 

[johnmatrix]

In order to simplify things, I disconnected my source from the amp. However, this created a large amount of grounding noise. I have the pot, ground for the amp section, inputs, and rcas (through the pot) going to the power supply ground with that ground tied to chassis with a ground loop buster circuit. I am curious if anyone has any ideas on what could be going wrong.

 

[ARwCoco]

Check out post #874 in the starving student thread

Best explanation I have seen/read

 

[johnmatrix]

I have the amp cased and ready to go except for the grounding issue. I did some investigation and found that when I turn off my room light and the receiver on the opposite side of the wall the noise gets quieter. Also, if I switch outlets the noise also decreases and almost disappears. I am assuming I have a dirty ground or something like that, but I was wondering what steps I can take to alleviate the problem. I have tried disconnecting the amp from earth ground to no avail so I am assuming the noise is coming from neutral.

 

[Juaquin]

Well, short of fixing your wall wiring, you could isolate the nuetral channel as it enters your power supply. I don't have enough experience to suggest the best method for this though.

 

[Pars]

I'm not sure you fully answered my question in post #2. With the amp off and unplugged, what does the resistance from PSU ground to the chassis read? Same as the resistance of your ground loop buster, or 0 ohms? If 0, then something is grounded to the chassis and is bypassing your ground loop buster.

Otherwise, I would try the amp in a different location (building, etc.) first before I started tearing into my house wiring.

 

[johnmatrix]

Pars,

That is a very useful test you suggested. I tested the ground to case resistance for the input jacks, pot, output stage, power supply and they all read the same resistance. Also, there was 0 voltage reading between all of them when the amp is running.

I tried upping the capacitance in the ground loop breaker and it seemed to help. Right now I am at 20 kuF which seems excessive. Increasing the resistance does little. Does anyone know why it works?

 

[johnmatrix]

I tested the resistance to ground again between all the grounds in my amp and the case. The resistances were the same for all of them (20 ohms). So it appears all of the grounds are only connected to the amp in one place. The ground noise does get louder when I turn on the light in my room and when I move outlets it gets slightly better.

However, the problem is still not solved so does anyone have more suggestions? I can't rip into the wall because I live in an apartment. Should I perhaps look into power conditioning or isolation transformers?

 

[johnmatrix]

I confirmed the problem by taking the amp to another person's house and there was no noise present in the system. I then measured the difference between earth ground and AC neutral and found 110mV difference between the two. Is this normal or out of whack?

 

[Pars]

Quote:

Originally Posted by johnmatrix /img/forum/go_quote.gif I confirmed the problem by taking the amp to another person's house and there was no noise present in the system. I then measured the difference between earth ground and AC neutral and found 110mV difference between the two. Is this normal or out of whack?

I would think that would be about normal. Isn't neutral tied to earth ground at the service panel? You are saying that the amp operated fine at the other person's house? If so, you have your diagnosis.

 

[johnmatrix]

Well I finally fixed the issue and it turns out it has nothing to do with grounding. Once I had decided on the AC being the problem I switched outlets and heard less noise. However, I noticed when I approached my room's lamp the noise got louder. My guess the phones were acting as an antennae and something was not connected. So I opened my O2s and found that one of wires in the right channel had been disconnected. I guess without both + and - connected noise was induced. I soldering the wire back together and problem solved! Thanks for the suggestions, I learned a lot about how to properly ground an amp even if that was not the problem.

BTW, who designed the connection between the wire and driver in the O2, a dumb monkey?

 

[spritzer]

Quote:

Originally Posted by johnmatrix /img/forum/go_quote.gif BTW, who designed the connection between the wire and driver in the O2, a dumb monkey?

Yup

This was fixed in the Mk2 though.

 

[SiBurning]

What kind of light? This kind of interference usualy happens with flourescents, but not always. It'd be nice to have it in the record for anyone searching the forum for ideas.

 

[johnmatrix]

Quote:

Originally Posted by SiBurning /img/forum/go_quote.gif What kind of light? This kind of interference usualy happens with flourescents, but not always. It'd be nice to have it in the record for anyone searching the forum for ideas.

Yep, It was a fluorescent bulb.