Uses a Vu Meter as a tiny percussive hammer.
Checkout this video; rB5UPjEjBlM of me assembling a vu-perc module, it will help you assemble yours.
There is a mod available for the blue vu perc kit here.
Solder small components (NOT jack sockets, switch and potmeter).
Put all big components (jack sockets, switch and potmeter) in the circuitboard and mount them with the nuts to the front panel, after this you can solder them to the PCB.
Making the vu meter, remove the vu meter enclosure with a cutter, and carefully cut a peace of the side to make it smaller (see images below).
Look at the images below and improvise.
There is shrink tube around the copper flap, this helps protect the vu meter hammer from not connecting to GND via the copper flap.
Wires connect as shown. I spray painted white paint over the piezo element so it cannot oxidise.
On the end of the copper flap there is dampening attached, this will remove high frequencies.
There are also more then one extra copper strip soldered to the back on the copper flat. This can
result in a snare like ratle when the metals strips vibrate and hit each-other.
A spring is soldered to the the end of the copper flap, the sound in generates is much different from
the hitting of a copper strip.
The spring is made of a material that cannot stick to solder, so its not easy to make it stick to it, you
can use a pin from a LED or resistor and use that to hold it in place with excessive solder.
To prevent the vu-meter hammer from connecting to the spring you can slide a peace of sleeve from
the wires over the end of it.
You can also use different vu-meters, most will work.
This is a mod for VU-Perc Blue. it will make the extra gate input respond to 5v signals. before it only responds to 10v gate signals (negative voltages are ignored by this input).
Basically you add a 10k resistor in series with a diode (i used a 4148), and grom from the middle gate input to the vactrols switch input on the jack socket.
You can also remove the smd 4148 from the PCB, but it wil function the same with it on it, if you leave it on it the LED from the other input wil light up.