How do I test a piezo pickup in an acoustic?

[Mincer]

OK, this is for an Alverez, and the specfic preamp model is a System 600T MK II. There is no output, although it is a fresh battery. The tuner doesn't pickup the strings, and there is no signal out of the jack. The preamp appears to be working, but I am not sure. I'd like to test the pickup itself, which is where I am guessing the problem is, but I am not sure. How do I test it by itself, and furthermore, if the pickup is working, how would I test the preamp? The preamp is plugged into the jack of the guitar by a 1/8" TRS plug...the piezo is plugged into the preamp with a much smaller mono plug. Any ideas?

 

[Mincer]

Re: How do I test a piezo pickup in an acoustic?

OK, I figured out what it is...somewhere in the cable from the pickup to the preamp (it is a braided 2 conductor cable) the braid and the core are touching. So, it is grounding itself out. I tested this by testing for continuity on the meter...on the tip and sleeve of the tiny jack on the end of the braid. Inside the jack, it is soldered correctly, so I am not sure where in the wire this break is happening. Possibly the whole wire or pickup needs to be replaced I am guessing.

 

[tone4days]

Re: How do I test a piezo pickup in an acoustic?

i am guessing a disconnected wire inside the body leading from the piezo to the output jack

that, or a hosed wire/connector

but i am a bit confused ... is the preamp onboard or outboard? ... is the tuner onboard or outboard? is the piezo a bridge transducer? if so, does each string have a separate piezo signal from its own transducer or is it a common one for all 6 strings? or is the unit a body transducer? or something else?


edit: we cross posted ... yeah a short or open would do it ... can that wire be replaced with a fresh, sturdier one?

 

[Mincer]

Re: How do I test a piezo pickup in an acoustic?

Preamp and tuner are onboard, attached to to piezo with a tiny wire and a tiny jack on the preamp. Single strip piezo for all strings, under the bridge, with the braided wire 'hardwired' to the bridge. Possibly changing the wire might work, but it is pretty delicate work in there.

 

[tone4days]

Re: How do I test a piezo pickup in an acoustic?

hmmm ... i am not so sure now ... i am not 100% sure of how you tested continuity ... if you tested the wire - all by itself - not attached to anything, then it is a valis test ... but if you tested it while one end was hardwired to the bridge, you might have gotten conductance through the piezo itself ... we are actually talking very small voltages needed to activate the piezo, so the meter itself mightve given you a false positive for a short between the conductor and braid

 

[Mincer]

Re: How do I test a piezo pickup in an acoustic?

the jack on the other end of the piezo is a mono 2.5mm plug. one of my tests for continuity was to connect the tip and the sleeve via the meter, and it beeped. i unscrewed the plug, saw where the wires were soldered (the braid to the sleeve, the inner wire to the tip), and tested the wires themselves...and got a beep. so my guess is something is connecting those 2 wires, somewhere.

 

[tone4days]

Re: How do I test a piezo pickup in an acoustic?

yeah, thats how i interpreted what you wrote

what i am trying to say is that your continuity test might be misleading you

as i understand it, a continuity test sends a dc voltage/signal out one probe and measures the resistance (i.e. voltage drop) that is observed across the probes ... if there is no voltage drop detected, the box beeps ... the thing is, the piezo crystal might not cause a voltage drop at all ... (in fact, thats kinda exactly how a piezo crystal works - google piezo electric effect in a crystal lattice) ... this could lead you to think there is a short between tip and sleeve (or braid and conductor) ... the cable might be fine, not shorted ... and yes, it also mightbe shorted and your diagnosis is correct ...

so the trouble might be the piezo itself, or something else 'downstream' from that source

if you can replace that little cable, that could help diagnose it

 

[Mincer]

Re: How do I test a piezo pickup in an acoustic?

gotcha...this is kinda what I feared...i might try to replace the cable and see if that changes things.