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Permalink Reply by Clark Rowden on November 15, 2015 at 10:38am

Paul, I recently tried just that - already having a blend pot that is commonly used on a bass guitar, one of these to be specific:

http://www.stewmac.com/Pickups_and_Electronics/Components_and_Parts...

Two piezos were used on a tuna tin (small) resonator CBG, one right under the bridge and one on the sound board 1/3 the distance from the neck in the middle of the box.

The result was that the sound board piezo was rather dull and the bridge piezo was really brittle and bright and the only usable tone was dead in the middle.

Better placement of the piezos would definitely worked out well but I had already hot glued the piezos in place so, I just yanked out the blend pot, wired the piezos in parallel and used a volume pot.

Any way, the concept is very doable but you need to tape the pickups in place and test until you find they're sweet spots.

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Permalink Reply by Paul Craig on November 15, 2015 at 12:06pm

I've learned that a piezo under the bridge is very bright. The bar type piezo work better in that position to my ears. Placing a piezo on the low/wound string side and one on the high/solid string side half way between the bridge and neck would probably work best. You could blend more to the low side for rhythm and blend to the high side for solo time or just mix to get what you want out of it. I'm thinking that 500k is the highest value for those pots, 1meg would be nice. Could use a balance pot from a old stereo if you have one lying around.

I like to use double sided tape for putting the piezo to the sound board. It easier to move around to find the sweet spot and you can double or triple the tape if one layer doesn't take enough harshness out of the response. Put a layer over the top to stop feedback.

At least you proved that it works. Thanks, I didn't have to lift a finger except to type. LOL

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Permalink Reply by Paul Craig on November 15, 2015 at 12:33pm

Thinking more on this, not sure that a balance pot and a blend pot work the same way or not. I think a balance just diverts signal from side to side and both in the middle like a on/on/on toggle switch while the blend pot increases/decreases signal from one side to the other once it moves past the middle position.You could still use the balance pot, but with a different result. Some car stereos had a Fader pot that acted as a blend for the front to rear speaker mix, but you would have to have an old one to have individual pots.

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Permalink Reply by RTZGUITARS on November 18, 2015 at 7:36pm

Originally Fender cut the treble of Telecasters by mounting caps on the volume pots input and output. You can fine tune tone many ways when you have volume and tone pot with caps.

You can make a amp out of a LM386 chip with just 2 caps on the speaker output this is where you set the tone for the amp. Some really good responses here.

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Permalink Reply by Paul Craig on November 18, 2015 at 9:28pm

Good info, thanks for that.

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Permalink Reply by darryl kernaghan on November 18, 2015 at 10:49pm

A piezo is effectively a capacitor in a way,Maduro Bob did a piece on it a couple of years ago,i've tried a piezo in a tone circuit,[in place of a cap], a couple of times with varied response,and messing with how you mount it in the box,it can bleed some treble off,and double as a secondary pick up at the same time which opens a whole other can of worms,so if you are going to try it,make sure you mount your piezo where it doesn't introduce highs that in turn need toning down,discs are notoriously variable in output,so it's hard to measure and duplicate,cheap caps vary a bit too,but better than discs

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Permalink Reply by Scott aka Farmer Ted on November 19, 2015 at 7:40am

This is a basic testing rig as described in a Youtube video on tone capacitors, to help builders check which capacitor may work best for any given guitar that does not have a tone pot/cap installed already.

The different colored parts at the top center represent the builder's chosen assortment of capacitors based on capacitance (how many uF, for example 0.01uF) and also different brands of capacitors. Yes, different brands and quality will make a difference in overall tone variations. As the drawing shows, there is an "in" and "out" jack. Each jack is mounted and grounded to the chassis (metal box). The + lugs of those jacks are connected to each other...AND to one side of a 180k ohm resistor ( a 1/4 watt value is fine). The other side of the resistor is connected to an alligator clip lead, so it can be connected easily to the "in" lead of any one of the capacitors. The "out" side of each capacitor should already be soldered to the chassis/ground.

Once a capacitor is chosen and connected to the alligator clip, plug the guitar into the "in" jack, and the "out" jack to your amplifier.

In effect, this test rig will save time and frustration when deciding which, if any, tone control & capacitor you may want. Remember one thing...guitars can have many combinations of components, woods, strings, boxes, scale, etc. and each combo can manifest it's character differently through any single or combination of pickups, and even the specific amplifier used.

Add to that the idea that each of us hear/experience the sound of a guitar differently. In other words, what sounds good to me can sound different to another person.

Hope the diagram & info helps.

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