[sdiy] NEWBIE REQUEST; PIEZOS

[harry]

Hi all  (newbie or not)

I use piezos IN the plastic case.  I use a small "wadcutter" pellet
(pellet gun ammunition with a flat nose) epoxied to the center of
the piezo disk. This lowers the resonant frequency and makes the
low-end response much better.

The piezos are usually about .01uF... so if you know the input impedance
of the mic input, you can predict the point where the low end rolls off.
This makes a natural highpass filter. Better response means higher impedance, so

an opamp buffer is a good idea.

Voltage can EASILY exceed 30V....  I use series (connected anode to anode)
zeners to clip the signal at a reasonable voltage, way above the normal clipping

range (like 6-12 volts).

You can make a capacitive divider to lower the voltage... but it will mess up
the
frequency response. If the shunt cap is small, this might be GOOD by limiting
the HF response.

Now you kids go away and don't bother yer elders. I KNOW you are gonna
put these on I-Beams and Anvils and Tuned Brake Drums (yeah try it) and keep
me up all night with yer bangin' on em with ball-peen hammers... and then
AMPLIFY
the result...

...and call it "music"

ok I'm down with it  ;^)

H^) harry

Toby Paddock wrote:

> NIKOLAS,
> I've been doing some of that lately too. Fun stuff.
> I used 1/4" mono jacks and plugged them into my radio shack mixer
> mic inputs set to -20dB. They are very sensitive. Insanely sensitive.
> I'm hoping that I don't blow the mixer input. It also worked using the
> line input to make it less sensitive.
>
> For the mono jacks, the metal base disk went to the sleeve for ground
> and the top thin metal contact went to tip. For stereo, both base disks
> to sleeve, one top contact to ring, the other to tip. Mmmmm... stereo.
> I'm having good luck with 2 mics on one metal thing for stereo.
>
> I will probably add back to back diodes across it to limit the voltage to
> 0.7V for protection. If I held the piezo around the edge and thumped
> it with a pen, I got something like 30V.
>
> I think you should be able to add a capacitor across it to lower the
> voltage. My (questionable) theory is that they are a charge source
> and capacitor. Adding capacitance will lower the voltage and not
> change the frequency response (much). Also should make it less
> sensitive to loading by the resistance of the mixer input.
> Haven't tried it yet.
>
> Good luck and I'd like to hear how things work out.
>
>  - -- -  Toby Paddock
>
> ----------
> From:   PATTERSON[SMTP:sanpatts at ozemail.com.au]
> Sent:   Saturday, June 02, 2001 3:39 AM
> To:     synth-diy at node12b53.a2000.nl
> Subject:        [sdiy] NEWBIE REQUEST; PIEZOS
>
> Hey all,
>
> My first post to this list!
>
> To cut to the chase, I am looking to 'mic' up some metal, and associated
> materials. I have some Piezo Electric Transducers, and some 1/4" jacks, mono
> and stereo.
>
> I can solder alright, and that is no trouble.
>
> My question is; is it okay to wire the Piezos to the jack, and patch that
> into my mixer, amp, speakers? Or, do I need a circuit, power (psu) or
> something else? Can you please offer your suggestions, circuits, or
> what-not?
>
> Further, what is the ring/tip/sleeve configuration on a standard 1/4" jack?
>
> Any, and all help would be great!
>
> Thanks heaps,
>
> NIKOLAS