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Electric Viola Wiring


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So I'm actually going to try and start this project soon, but I decided that before I go and build the instrument I wanted to get all the electronics sorted out and working. So I have a couple uneducated questions about the Helmke circuit. The parts list he's provided is no longer up to date so I can't find the parts he suggested, I went through and found parts that I thought were similar, but I'm an electronic noob and don't know if the are actually parts that work. So my main question is whether you could checkout a couple of parts and make sure the are satisfactory.

He said on his page that, "The input and output capacitors (0.033uF and 0.1uF) should be something good for audio"

I found:



"The 4.7uF capacitor can be tantalum or electrolytic, doesn't have to be anything fancy"


"The 20pF capacitor is now 1pF - really just a tiny little value to shunt RF to ground. "


Those are the parts I was unsure of, if anyone has the time to check and see if they would work, or suggest better ones that would be really great.

Also has anyone tried the solder wire from Guitar Fetish? I'm going to be getting some other parts from the project from there and was thinking about getting that wire, but I was going to pick up a 25 watt iron from Mouser for cheap. Last question. Should I just pick up some insulated wire from radio shack or get my wire elsewhere?

Thanks again for all your help. I wouldn't even be this far without all the information on this forum.

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You might want to see if you can find a complete piezo system...I might have a bit of a search later...but there are some cheap things about for stringed instruments. The manufacturer Artec comes to mind. My daughter plays violin and I have two electric instrument here, on I bought for myself, looks like a pretzel...but only cost $60 new...it's made of plastic, but does play and actually sounds quite good plugged in. It has a piezo strip that sits under the bridge a preamp with volume and tone on the instrument, and can even power headphones from it...

On it's own it would probably be cheaper to buy something like this and scrap it for the electronics.

I know I ahve a few piezo systems for guitars around here of name brands with preamps with graphics and at least one branded fender and has a chromatic tuner in it...again, it wasn't that dear to buy...not sure if ideal for this application, but they are all shielded in metal boxes and ready to install with mini pone plugs and such for connections...

Otherwise, there are a heap of preamp kits about that might well do the job adequately...in the sustainer project and other things I have used the "PreCHAmp" preamp and intend to try it myself for an electric guitar piezo project I am working on. I know I ahve used them before for this application with a bit of success, so you may want to consider that too. On a basic level, you are really trying to get a bit of an impedance match, tone and such could be adjusted at the amplifier side of things outside of the instrument...

good luck


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Hmm... Well, the electronics in the plan are fairly inexpensive. I might by them and see if I can succeed in building my own before I buy a system, both for money reasons and just because I enjoy messing around with stuff like this (even though I have very little experience).

I did come up with one more question though. In order to add a volume control to the system would I just put the pot before the signal reaches the piezo buffer? and also what size pot would be suitable?

Edited by customguitar
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I did come up with one more question though. In order to add a volume control to the system would I just put the pot before the signal reaches the piezo buffer? and also what size pot would be suitable?

Put it after the buffer. Size is a good question. I would think that since it would be after the buffer that a 250K or 100K audio pot should work.

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