Double Bass How to test a broken K&K Bass Max pickup?

[pod222]

I think my K&K Bass Max pickup died at the last gig. It crackled for a while and then gave no signal to the amp. The cable was brand new, no dead batteries in the signal chain, etc.
My guess is a short or broken wire between the piezo element and the 1/4 inch connection. Anyone know how to test this, perhaps with a multimeter? Thanks.

 

[Francois Blais]

It may be the jack, which is quite cheap.
Move the plug in the jack to see if the sounds come back.

 

[Bob Gollihur]

I think my K&K Bass Max pickup died at the last gig. It crackled for a while and then gave no signal to the amp. The cable was brand new, no dead batteries in the signal chain, etc.
My guess is a short or broken wire between the piezo element and the 1/4 inch connection. Anyone know how to test this, perhaps with a multimeter? Thanks.

If it crackled that would typically point to the connection between wires at or near the piezo, located where the straight cable meets the circular piezo section. If they fail at all, it's usually due to stress at that joint, and if you don't get any noise by gently manipulating (gentle squeeze and/or very slight bend) I would suspect the jack - complete failure (no signal at all) is very rare.

A multimeter (VOM, use the resistance scale) at the other end of a known good cable plugged into the Bass Max should show significant resistance. If there is no reading it would indicate an open circuit, meaning that either the jack connections or piezo area connections have failed. I'd go for the jack, trimming back any shrink wrap so you could get at the jack connections to inspect and use the multimeter to directly measure resistance at the wires from the pickup.

 

[pod222]

Thanks Bob. Funny that you would respond - after reading everything on your website, I decided to start using my Fishman Pro-Eq again. Being a newbie, I though I should stop using it after I got the Genz Benz Shuttle 6.0 - why have an external preamp when it has an onboard one, I thought? Your article on impedance convinced me I should use it again. (Not that I understand very much about impedance, notwithstanding the excellent article). Anyhow, at a gig this weekend, I ran through the Fishman and in the Aux In on the Genz Benz. Worked like a charm. Now I need a bigger cab...

Thanks for all your help.

 

[agedhorse]

A multimeter (VOM, use the resistance scale) at the other end of a known good cable plugged into the Bass Max should show significant resistance. If there is no reading it would indicate an open circuit, meaning that either the jack connections or piezo area connections have failed. I'd go for the jack, trimming back any shrink wrap so you could get at the jack connections to inspect and use the multimeter to directly measure resistance at the wires from the pickup.

In the name of accuracy, if the Bass Max is a true passive piezo pickup (and no surrounding circuitry or buffer), there should be almost infinate resistance when measured with a DC ohm meter. (note that some multimeters use an AC test signal and may give inaccurate DC resistances on incuctive or capacitive loads)

A piezo pickup is essentially an open circuit at DC (and very low frequencies). It's a capacitor with a piezo-ceramic dielectric that generates a voltage under mechanical stress. It's impedance would have to be measured with an AC signal and the impedance will decrease as frequency increases. That's how you tell if a piezo element is electrically intact. You can also measure it's capacitance and compare it with a known good unit or a manufacturer's test spec, though the reading must be adjusted to whatever standard cable length the standard was measured to as cable also has capacitance but the dielectric is different and it doesn't (hopefully) generate any signal on it's own.

Hope this helps clarify what's going on inside the pickup itself.