Posted by jeremy lee on October 11, 2009 at 9:41pm
i'm a shop teacher in chicago. i've started my kids on a lap/slide guitar project fashioned out of a piece of lumber and amped with a piezo. we are trying to figure out how to connect the piezo to the guitar and electric guitar amp with out all the feed back and squealing. i've heard it's impossible to run a (non-magnetic pick up) piezo to an electric guitar amp. some say it has to be an acoustic amp.
the piezo does run with out squeal on clean channel, but to the kids, it is not nearly as awesome as running it through distortion. can you guys help me save this project? any ideas? solutions?
(using a male head phone jack as opposed to a guitar chord or female jack)
Thanks for the useful knowledge every one. I greatly appreciate it.
I tried sealing the piezo with a with an old school gummy eraser and that seemed to work.
I was able to tinker with the volume and the gain enough to get some good crunchy distortion with out the squeal.
Like N. King mentioned, it seems like a little squeal just comes with territory.
Showing the photo using the "camera" icon on the editor:
I would definitely look at isolating the piezo from the "room sounds". Maybe you could route a pocket for it under the bridge, and cover with a thin piece of plywood? The primary signal should be strongest right at the bridge, too. You should be fine running into most guitar amps, although some are reported to have problems with the high impedance: in that case, there are plans out there for "FET buffers" which can help out, e.g.: http://scotthelmke.com/Mint-box-buffer.html
I got some decent results out of a piezo by mounting it onto a small piece of hard wood befor e mounting it to the body (inside), as it seems to make the tone a bit softer without using an extra preamp or eq.
This was done after several rounds of experiments. Maybe you could use the experimental stage as part of your course for the kids?
In the courses I put on I found that the use of self discovery keeps the kids interested in the build they are doing, especially those who are not so gifted in the handicraft aspect..
I just got mine to work on a typical Cigar box body. My first attempt did not work well, too much hum, and not enough guitar. Some have suggested you need to solder it properly for it to work right. but on your instrument it is all out in the open. I encased my piezo in dense foam rubber and it sits in the box under the bridge. Perhaps it needs more isolation from the environment,
In my experience, you can plug a piezo into any typical guitar amp. The clean channels seem to work out pretty well, but once you start adding distortion or gain is when you start getting that squeal, and it seems to be more or less unavoidable. The suggestions Jkevn provided can help to cut down on the squealing, but depending on the volume, how close you are to the speaker/amp, and the amount of distortion used, that squeal will still be there. Nature of the beast, I suppose?
On a side note, the body shape you have got going there is really cool!
As was already mentioned, piezos act as microphones rather than picking up movement of the strings like a magnetic pup. If you are getting good sound where it is now mounted (except for the feedback of course) try cutting a square of mouse pad large enough to cover the piezo and temporarily using it to shield from vibrations coming from other sources (speaker etc) A thick layer of silicone or hot glue covering the piezo will block unwanted vibs from hitching a ride, a thin piece of wood will make it look better.
All of that is meant to say that you only want the sounds from the guitar's vibrations to be "heard" by the piezo, you want to block it from everything else. Turn the speaker away from you and then turn your back to it and see if there is any improvement.
So what kind of squealing are you getting? Pizos act like mics so unless they are getting feedback from something...
Piezos can connect to a standard guitar amp and we usually solder the piezo to a 1/4" mono jack (radio shack brand perhaps) and use standard 1/4" cord to the amp. I personally use a preamp, but that's not mandatory (I don't think). Yep, looks from the picture you have a 1/8" cord. Where did you get the piezo from?
... unless the headphone jack is stereo and you have some cross wires or bad connection.
Replies
I tried sealing the piezo with a with an old school gummy eraser and that seemed to work.
I was able to tinker with the volume and the gain enough to get some good crunchy distortion with out the squeal.
Like N. King mentioned, it seems like a little squeal just comes with territory.
I would definitely look at isolating the piezo from the "room sounds". Maybe you could route a pocket for it under the bridge, and cover with a thin piece of plywood? The primary signal should be strongest right at the bridge, too. You should be fine running into most guitar amps, although some are reported to have problems with the high impedance: in that case, there are plans out there for "FET buffers" which can help out, e.g.: http://scotthelmke.com/Mint-box-buffer.htmlThis was done after several rounds of experiments. Maybe you could use the experimental stage as part of your course for the kids?
In the courses I put on I found that the use of self discovery keeps the kids interested in the build they are doing, especially those who are not so gifted in the handicraft aspect..
On a side note, the body shape you have got going there is really cool!
All of that is meant to say that you only want the sounds from the guitar's vibrations to be "heard" by the piezo, you want to block it from everything else. Turn the speaker away from you and then turn your back to it and see if there is any improvement.
Piezos can connect to a standard guitar amp and we usually solder the piezo to a 1/4" mono jack (radio shack brand perhaps) and use standard 1/4" cord to the amp. I personally use a preamp, but that's not mandatory (I don't think). Yep, looks from the picture you have a 1/8" cord. Where did you get the piezo from?
... unless the headphone jack is stereo and you have some cross wires or bad connection.