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Post subject: Re: Help! - Wireless mics signals bleeding into guitar amp!
Posted: Wed May 27, 2015 5:32 pm
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TimsAudio:
I built the shield for the inputs out of the 9V battery jacket per your instructions and grounded it to the front chassis just in front of the connectors. Incidentally, I actually have a hole punch, and made holes for the capacitors to stick through, so I was able to get it right down pretty much against the IC chip (of course, wrapped with electrical tape and siliconed in place). I performed the test you spoke of using a 100K resistor before and after installing the shield, and I was honestly able to tell an improvement in the amount of input noise here at home. So thank you for that!

Good news: In digging through my collection of old, forgotten gear, I actually found a 6' piece of XLR cable I used to use in an effects rack; and believe it or not, it has a foil shield (probably why I used it in the effects rack...). I sit right beside my amp at the theater with it tilted back on my left side, so the shorter cable won't matter, I only need it to reach around my chair.

So I am right now in the process of building your shielded guitar cable suggestion, but won't be able to test it out until Friday night. So stay tuned, wish me luck, and I'll let you know if it helps on Saturday.

I'll also check this thread a few more times between now and then in the event you or anybody else thinks of anything else to try.

Thanks!

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Post subject: Re: Help! - Wireless mics signals bleeding into guitar amp!
Posted: Wed May 27, 2015 8:52 pm
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It sounds like you're on track to better sound and beating the RF gremlins.
The only other thing I might suggest is to ground the speaker frames. Sometimes they act like RF radiators. Some speakers come with grounded frames, but I don't think these are.


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Post subject: Re: Help! - Wireless mics signals bleeding into guitar amp!
Posted: Fri May 29, 2015 10:03 am
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TimsAudio:
I grounded the speaker frames on the 212R with a grounding wire from the chassis to the frames per your suggestion.

The noise-cancelling guitar cable has been built and tested here at home to at least be certain of a signal, and to make sure the 2nd conductor was insulated at the guitar-end (accomplished this with a tiny bead of that silicone I used on the input shield from the 212R mod).

Additionally, and I don't don't know if this counts as a valid test or not, but as an experiment I ran an audio signal through my NADY wireless into my practice amp in the bedroom, and then plugged up the Strat and 212R near the transmitter in the living room using the noise cancelling guitar cable, and heard no RF bleed. -- I had the guitar cranked up all the way and tried each 5-way switch position, and had the volume on the amp at a substantially higher volume than I would probably ever use, reverb up also.

Now, I understand that with the NADY being an older wireless-unit I am probably transmitting at a substantially lower frequency than the newer wireless mics at the theater, but with the transmitter less than 2 feet away from the guitar and amp, and RF being RF, I would think I would have heard something; especially with the transmitter pack output level cranked up. -- Although it would've been nice if I had thought of trying this before any of the mods, to have a benchmark to compare to.

Then, as an experiment, I unplugged the noise cancelling guitar cable and plugged back in the Monster cable with the same results as above: No RF bleed-thru.

So now I'm wondering if perhaps grounding the speaker frames may have been what we needed to do all along?

Either way, I guess my setup is as RF-proof as it can be for now, thanks to your suggestions. I am going to go in early to the theater this evening to get set up and try the Monster vs the noise-cancelling guitar cable experiment all over during mic-checks, and will drop you a line tomorrow (Sat, 5/30) to let you know how it went.

Thanks!

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Post subject: Re: Help! - Wireless mics signals bleeding into guitar amp!
Posted: Fri May 29, 2015 10:16 am
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Best of luck -- it sounds as though you've done everything humanly possible to resolve the issue. Post a report after tomorrow evening's rehearsal.

Arjay

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Post subject: Re: Help! - Wireless mics signals bleeding into guitar amp!
Posted: Fri May 29, 2015 10:36 am
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I wouldn't expect that the speakers would the main culprit. Just trying to cover all the bases. Interference is usually not completely eliminated, just reduced. Every little change reduces it further.
The frequency differences between your NADY and the other packs could make a significant difference, so the acid test is at the theater.
The only other thing I can think of is to shield the cavity and cover of the guitar with copper tape.
But you've done as much as you can for now. I hope it works out and drops the interference to an acceptable level.


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Post subject: Re: Help! - Wireless mics signals bleeding into guitar amp!
Posted: Fri May 29, 2015 11:36 am
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Retroverbial (Arjay):
Actually tonight, tomorrow and Sunday are performances, audiences and all, not rehearsals. Thanks!

TimsAudio:
Just a quick FYI: The cavities and scratch plate of the guitar are already lined with copper tape, but thanks anyway for the suggestion!

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Post subject: Re: Help! - Wireless mics signals bleeding into guitar amp!
Posted: Fri May 29, 2015 8:53 pm
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Well, the RF bleed from the wireless mics wasn't completely gone, but we knocked out about 70% of the signal from what it was before using the short noise-cancelling guitar cable. I had to literally bend over with my ear next to my speakers to hear what signal was left; so I would call that a success.

With just the Monster cable there was still a very noticeable improvement. I could still very faintly hear the mic bleed while sitting in my chair, but if I stood up it was imperceptible, and nobody else in the pit could hear it at all -- so I would call that a success as well.

Most importantly, we satisfied the soundman. The overhead mics aren't rebroadcasting the bleed signal, and I don't have to listen to him complaining anymore!

I'm thinking it was a combination of the input shielding and grounding the speaker frames that improved the major signal bleed, and the noise-cancelling guitar cable had much less bleed-thru than the Monster cable. So I'm going to stick with the noise-cancelling guitar cable from here on out.

Thank you, TimsAudio for everything! I'm going to call this one solved.

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