Syntrillium Backup Forums :: View topic

amoore · Posted - Tue Jul 29, 2003 3:33 pm

I am recording our church services onto our soundbooth computer through our record out on the mixer. I have tried using dollar store cables and with what we had already and it worked alright but with a hum. I assumed I was loosing the balance going from (board-->cpu) XLR--->down to a single RCA then to split into red and white and mixed into a stero mini jack. Yeah I know its like there you go, so I purchased a cable 1/4"--> stereo mini and added the 1/4'-->XLR adapter to plug into the board. I still get the hum. I have read several articles on this and would like to know how to fix it. I read about using the same power source, to grounding the cpu case(which would be already, through the power cord). Anyways of course I can remove the hum using the noise reduction but as all of u would agree the less u have to remove the closer the quality to the real sound. Anyways please let me know. This would save me 10-15min a service.

twright · Location: USA

SteveG · Location: United Kingdom

If, (and it's a big if) this hum is caused by a grounding hum loop, one thing that you can try with relative safety is to remove the signal braid ground from the mixer feed to the pc, and just leave the PC signal ground connected - in other words it will end up looking as though you've not connected the signal outer braid at the mixer end.

This will break the hum loop without removing the main safety ground connections, which is what you shouldn't do under any circumstances. Strictly speaking, you don't need to join the braid to both the mixer and PC if they are sharing a common ground, because it's only a screen, and not a return signal path. But if this cures the hum, you will have a slight problem, because there's a fairly good chance that extra 'hash' will be introduced into the signal by using the common ground as a signal return. The correct fix for this is to use an isolating transformer in the signal line, which will keep the grounds artificially separated, whilst retaining the connection integrity.

And if the mixer and PC are both running from the same supply, it's worth checking the supply cables anyway to make sure that the grounding really is intact.

Graeme · Member Location: Spain

The source of a hum can be a real problem to find. The only practical way to approach the problem is to take it step by step until you find the part of the system where it is getting in.

Unhook all the connections, mic, mixer, etc. Start with the computer - disconnect everything from the soundcard inputs and try a recording - should be silence, of course (other than the base noise of the card itself).

Now connect the mixer output to the card and try again. Still no hum, then connect a mic to the mixer and see what that does. Take it slowly and methodically, the object is to isolate which bit of the system (when connected) cause the problem.

When you know which bit it is, you're half-way there.

motorhead6 · Posted - Wed Jul 30, 2003 7:13 pm

It could be your monitor too. Or about 90,000 other things. Flourecent lights etc...