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Need help-piezo only picks up inner strings.

Hey, guys.

I was a member of the old Yahoo group, and just joined this one. I recently built a 4 string, fretted baritone CBG tuned BEAD, low to high. The piezo pickup is imbedded in the bridge plate (a piece of red oak) and insulated with a piece of thin foam. The two inner strings come through great, but the outer two can barely be heard through the amp. I wouldn't think the piezo is defective since it picks up two of the strings, but I'm not sure.

Any ideas? Thanks,

Seane

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Permalink Reply by Don Thompson on November 21, 2010 at 8:15am

New bridge, two piezos. What is your saddle material? Wire up two and connect to jack, slip under bridge if possible, test. The vibrations of your outer strings are not enough to excite the single piezo.
Don

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Permalink Reply by MichaelS Country Boy Guitars on November 21, 2010 at 9:15am

I have done a single in bridge 3 string and it worked fine, but I don't put any foam in it when its in the bridge. Double does work better for me as Don suggested, give it a try. Make sure one of the piezo's is close to or under the low string, this helps.

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Permalink Reply by Josh Gayou (SmokehouseGuitars) on November 21, 2010 at 4:18pm

If the piezo is picking up the two inner strings then it isn't defective. It sounds to me like the foam is damping out a lot of the string's vibrational energy. Is there any part of the disc that is floating (not anchored to the wood)? If two strings are transferring through to the disc okay then all four should be working. This is a really bizarre issue.

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Permalink Reply by Skeesix on November 21, 2010 at 5:43pm

If the string spacing is wide enough that the piezo is directly under the two inner strings, but not directly under the two outer strings, that could be the problem causing the uneven response. If you want to keep a piezo under the bridge, then a solution would either be 2 piezos wired in parallel, or one wider piezo such as piezo film.

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Permalink Reply by Seane Crews on November 22, 2010 at 3:36am

Since there are a few different theories here, let me go into a little more detail on the pickup construction.

I made a cavity in the top half of the bridge with a 1.25" forstner bit, put some Elmers into the cavity, and placed the piezo in bras side up. Next I put a piece of thin foam on the ceramic side of the element to keep it good and snug, then sealed up the back with another thin piece of wood.

I have seen several references to using foam this way. SInce it is on the ceramic side of thee piezo, I wouldn't think it would affect the sound, but ya'll know a lot more about this than I do.

Should I have used C/A glue instead of the Elmers?

Seane

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Permalink Reply by Robert John Spotti on November 22, 2010 at 6:12am

Seane,I would think the glue just might be the problem.I would use silicone it will hold it in place and allow for some vibration.I'm curious to see what the final solution will be.Good Luck!

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Permalink Reply by Seane Crews on November 22, 2010 at 6:33am

Should I put ANYTHING (silicone or glue) on the brass side of the piezo, or just put it on the ceramic side? Would this hold it against the wood (bridge plate) firm enough?

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Permalink Reply by Robert John Spotti on November 22, 2010 at 12:10pm

Seane,I have found that everybody has different ways of doing things that is what make this so much fun.I have had some success with sandwiching my piezo with two pieces of furniture pads those little things you place under the feet of chairs and such to protect the floor.Piezos seem to work better under pressure if your firmly attaching your bridge just make a sandwich of foam.

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Permalink Reply by Don Thompson on November 22, 2010 at 12:21pm

http://www.artecsound.com/acou/piezo.htm
As I stated before your saddle is not in contact with the piezo, the vibrations on the outside strings are being damped by wood . The simple drawing shows what I mean, the saddle contacts the piezo therfore the string vibrations are equally transmitted to the piezo. Yours doesn't. No amount of changing glues will change the way your bridge behaves. A single piezo would certainly work on your soundboard but in your situation I would go with two and be done with it.
Don

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Permalink Reply by Robert John Spotti on November 22, 2010 at 10:52pm

Seane,When I built my first two guitars they were identical except for the amount of strings one being 3 the other a 4 on the second I put silicone around the piezo the response was vastly different.So much so I took it apart and removed the silicone.It made a huge difference.I finally had two similar sounding guitars.I'm speaking from experience only it worked for me.Both piezo were in exact placement,neck,box,scale length ,tuners and string brand were identical the only variable was the silicone once it was removed the problem was solved.Good Luck!

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Permalink Reply by Seane Crews on November 23, 2010 at 4:19am

OK, as Don suggested, I am going to first try using two piezos instead of one. What are the pros and cons of wiring the two in series vs. parallel? Just by looking at the diagrams, I would think that parallel would be hotter, but series would take the edge off a little bit. Then again, all of my prior experience has been with one so it's just a guess.

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Permalink Reply by MichaelS Country Boy Guitars on November 23, 2010 at 5:43am

Wire them parallel. Sounds better.

Seane Crews said:

OK, as Don suggested, I am going to first try using two piezos instead of one. What are the pros and cons of wiring the two in series vs. parallel? Just by looking at the diagrams, I would think that parallel would be hotter, but series would take the edge off a little bit. Then again, all of my prior experience has been with one so it's just a guess.