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OT: Help please! Piezo Contact Mic feedback issue


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I have wired up two piezo contact mics internally to my kalimba to make it electric. I did this quite a while ago. They are coated with an epoxy and both wired to the output jack. (EDIT: There is a hollow body to this instrument that you can't really see in the photo) I use two to capture the top and bottom sections of the Kalimba. Sounds killer, but I CANNOT play this instrument live because I have severe feedback when distortion is applied. Or even mild volume. No Feedback Exterminators help, even really good ones: see SPAM thread.

 

Is it feeding back because I have two piezos? Or is the amount of metal involved picking up every vibration in the room?

 

What solution would you suggest? I would try magnetic pickups if they actually fit, but when you look at the design, you'll see the impossibility of me using them.

 

img_0128.jpg?w=560&h=746

 

Sustain and bass is insane. Just wish I didn't have to worry about squealing speakers while I played!

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I also have a very limited understanding of acoustic pickup systems. I have a Barcus Berry but it was a very localized pickup and doesn't come close to the piezos. Mic'ing doesn't seem to pick it up well. Is there something I am missing? It IS directly wired to the jack... is their some component I am unaware of? Those of you with acoustic guitars: What is your experience with contact mics and do they feed back on you?

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I can think of a few things.

 

Sounds like you're using a guitar amp to amplify it? This could be part of the problem IMO. The frequencies emphasized by electric guitar amps are prone to cause more feedback issues IMO. Adding distortion will just make this worse.

 

also, are you using a preamp? Those piezos probably would sound better with a high input impedance (10M) preamp like a SHO.

 

I would use a SHO into a DI box into the PA, one with decent channel EQ will let you sweep the midrange to find any troublesome feedback freqs and eliminate them. Or dedicate a good rack EQ to really sculpt the tone. I suppose a decent EQ pedal with 10 bands or so might be an option too.

 

Also you do have to realize that acoustic instruments do have a "saturation limit" IMO, you can only get things so loud with them until they do start resonating with every noise and feeding back. I suspect you might need to turn down some or direct the sound away from you and towards the audience more.

 

One more thought, consider adding a phase switch to the piezo setup, sometimes unruly feedback can be squelched quite nicely by inverting phase.

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Thank you for replying.

 

Currently I just have it setup as Distortion into Amp, so that's probably not helping.

 

I have tried an Boss AD-5 as my preamp/eq. It had a preamp, feedback control, eq, and phase switch. Didn't do much to stop the problem. It did fatten the tone on the bottom end, but it didn't justify keeping the pedal.

 

I have the the Sabine SL620 in spam right now. Again, adds plenty of volume but doesn't stop the howl entirely. I suppose the distortion pedal is the problem, and when disengaged I can get a bit more volume, BUT this kalimba just sounds perfect with it. Could it be having two piezos?

 

Will be working on moving the amp position later today, but would like to eliminate the problem entirely.

 

Is their anything I could add (diodes, resistors) to the current simplistic wiring?

 

You have really gone out of your way to answer, so thank you.

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"Feedback eliminators" are junk IMO, a good 31 band EQ and a good set of ears is the true feedback eliminator

 

But that boss pedal should have been helpful, I suspect you're just at the limit of volume/feedback threshold.

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Thank you. Will try volume/positioning experiments.

 

Separate question: should I have a different pickup system for the kalimbas I am building? Would want buyers to not encounter these problems at all. Like, what would you install on this puppy?

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So I tried a different configuration, and even put the speaker outside the studio. At anything above a 5 on a 15w amp with this pedal: feedback. It's a Digitech PDS1700. I have used this pedal in line with my line input stuff, and of course no FB because there was no Mic situation. I am perplexed. Those who know: how would you put a pickup on this kalimba? Any type or brand?

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