Audio Systems: Ac buzz, gauge wires, video cart

Question
QUESTION: Hi Cleggsan
I'm having trouble with ac buzz.  I have some multi conductor, mogami cable with 2-18 gauge wires, 1 video, and 2-audio.  I'm sending ac down the 18 gauge wires.  I would like to use one of the audio lines to send a mic signal.  I have a 1.5v lapel mic. at one end, feeding a small battery powered amplified speaker on the other end.  All sounds good..... until I plug in the AC.  It's not powering anything yet, just present in the line.  It will power a video monitor in the future.
How can I filter out this noise.  I am only using hot and neutral, ground lifted.

I've tried 16v 100mf caps to eliminate the buzz but it brings my level way too low to hear.  

Thanks for taking the time to help novices such as myself.  It truly is appreciated.  

Let me know if you need more info.

Ed

ANSWER: I don't understand the setup - equipment on the other end and how you have it grounded, line lengths, etc.

Buzz or what is actually diode rectified current spikes running around is from either improper grounding, improper shielding or equipment malfunction (or faulty installations!).

If you are running a mic line parallel to a power line (which is a very bad thing to do!) you need severe shielding.

When you say "until I plug in the AC", which AC are you plugging in? The mic preamp?  Have you checked its ground and making sure the grounds are common so there is no ground loop? A ground loop is caused when two different circuits are drawing more than trivial currents and are grounded in two different locations.

So, these are some things to take a look at and see what you can learn about the buzz origins.  Then , let me know the results and we can take it to the next level.



---------- FOLLOW-UP ----------


wiring items   QUESTION: Sorry,   There is not much of a setup yet.  

Here are some pics and here is my goal.

Using this Mogami cable, 100', I will send video, audio and ac power to a video monitor from my video cart.   I will also be sending back a mic feed from the monitor so I can listen to the "director" as he watches the monitor.  It will feed the mini pre-amp/speaker.

I have had no problems with this setup while send DC power, but now I need AC.  I know sending mic signal next to AC is bad, but It the only way I've found to do what I need.


I've just connected the 2 18 gauge wires to an ac outlet (no ground).  I haven't connected anything to the other end yet.  It will power the video monitor at a later date.

I'm attaching the mic to one of the audi lines to feed back to my cart.  I can put the mic power switch at the monitor end or the cart end.  I found putting it at the monitor end was worse and am trying it at the cart end now.
It feeds directly to the mini speaker.  Both the speaker and the mic have their own power, isolated from the AC lines.

So my question is.....Can I filter this AC buzz.  I do know someone is doing something like this, but I am unable to ask their solution.

Answer
No, forget the filtering idea. You must find out what is causing the buzz coupling or grounding problem.  Best if you can put the mic or low level audio wires in their own cable but they MUST be shielded.  And, preferred that the mic wires also be twisted in order to cancel the induction from the power wires.  If you can check the mic at one end before it travels to the end of the line and see if you still have the buzz - which indicates a connection problem or a malfunction of something that is putting the buzz on the line.  A bad power supply with open electrolytic capacitor, for example, will do it.  Also, these little power pods that plug into the wall do not have filtered dc so using on of them has buzz on it by definition.

Cheers.