[sdiy] Frustrating RF Interference

[harry bissell]

Well todays yer lucky day, Jimmy...

Here is what I found...

The noise comes in on the OUTPUT cables... and it rides down the shield, 
through the
sheet metal. It does not really get to ground until it has run four or 
five inches through
the inside of the box.. to a "bus" pc board.

What I did was

1) Disconnect the RCA line out jacks, permanently
2) Add a ferrite bead (a BIG one - clamp on style) to the wires going to 
the 1/4" Phone and
XLR outputs.
3) Made a cable to go from the XLR outs to my recorder unbalanced input. 
You can wire
the XLR so that you get 2x the signal level. This lets you run the mixer 
1/2 as 'hot' and improves
the signal to noise ratio.

with these fixes I was able to record my CD direct to DAT with no hint 
of radio noise background.

There is no 'good' fix for this that I know of. Redesign from a really 
EARLY stage would be the only
way...

Hope this helps

H^) harry

Jimmy . wrote:
> So I got a used Tascam M-2516 mixer and now it is picking up FM radio 
> country music in my monitors/headphones. I've tried disconnecting 
> everything down to just the mixer and a single keyboard running off 
> the same power outlet to no avail. Everything works fine with my old 
> crummy Behringer mixer. Just can't figure this out.. I don't think 
> there is a ground loop and I'm using a short, high-quality shielded 
> cable.
>
> I've heard that Tascam back in the day didn't do much in their designs 
> to provide proper shielding and RF rejection. Now to my knowledge the 
> lowest FM station is 88.1 mhz; the signal somehow gets rectified 
> inside the mixer and becomes audible. Is there anyway I can filter out 
> say everything above 50khz on the line inputs and prevent the FM 
> signal from getting rectified? I've tried ferrite chokes, but I think 
> it will be too expensive for so many connections. Can anyone advise me 
> on how to add simple RF filtering on my mixer inputs?
>
> Thanks,
> Jimmy
>
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