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5 February 2012

Taming the Piezo

Not too far back I fitted a piezo pickup to one of my ukuleles. It was a cheap and fairly painless exercise. Today I'm going to talk about some of the mechanics of amping the instrument.

First let's get some technical stuff out of the way:

"Piezoelectric fields result predominantly
 from atomic layer displacements along
 the nanowire axis within both the core
 and shell materials."
 - American Chemical Society

Piezo pickups (AKA Piezoelectric pickups) work in a slightly different way to magnetic pickups. Magnetic pickups rely upon vibrating steel strings affecting the pickup's electromagnetic field whereas piezo pickups rely upon changes in pressure affecting the pickup's ceramic core. So in a nutshell, Piezo pickups are reliant upon picking up vibration through contact with the strings. This is why you fit piezo pickups under an instrument's saddle. And this is why you need a nice tight fit for the piezo to work at its best.

A feature of piezo pickups is that they output a far higher frequency range than magnetic pickups. You need to manage this if you want to get a good sound out of an amplifier. Piezo pickups are famous for producing clipping and buzz. And whilst this might sound ideal if your only interest is in recording punk ukulele, it is actually far from ideal.

If your piezo is passive (i.e. no pre-amp), then the job is all yours to fix. I've never managed to get a good sound out of an instrument with a passive piezo. If you have a pre-amp as I have with the UK2000, then you might be lucky.

The conventional solution to this problem lies in a device called a Direct Injection box. There are different flavours of DI box available, but they all roughly do the same thing: to match input/output impedence between pickup and amp, and to deal with pickup grounding issues. I've never owned a DI Box and they're expensive!

A selection of DI Boxes

The King Uke approach to this problem is to experiment with less conventional solutions.

It takes around 5 seconds when investigating a lot of pickup problems to discover that most hums, pops, clicks and buzzes can be solved by touching your finger onto something metal on your instrument. On my ukulele I can cut out all inteference by touching the jack socket or jack lead plug with human flesh. This is usually a good indicator that I've got a grounding problem. Whilst it's fairly easy to fix grounding issues with magnetic pickups, I haven't come up with a long term way of doing it with a piezo.

My solution then is to simply make the dirty hack a bit easier; Pressing flesh to the jack socket is not easy to do while you're on your knees delivering electric ukulele retribution. In the past I've used bits of wire, tin foil, basically anything metal to hand that I can use to run a line between the instrument and my body. One end usually ends up hooked inside my pants, but let's not dwell on that right now...

Today I present a new, more elegant version of the dirty hack.

I recently bought myself an anti-static wristband. It cost 99p off ebay and I had to wait about a month for it to arrive from Hong Kong. And it works!

Anti-static wristband

Wired up and dangerous!

And finally...

Whilst I hope that this post has made you smile, I also hope that it offers some insight to anyone who might be struggling with similar problems. What I'd really like - and the main reason for this post - is for some of the cleverer people out there in internetland to share some specialist knowledge. If you've got something to say... If you know how to tame the piezo... then please let me know!

1 comment:

  1. Tin foil and sticky tape for me