Introduction: Squeal & Scrape
This project can be made by milling a PCB using files found on github or by using vero board as per the illustration.
Some soldering is required so the usual equipment is needed:
IC - LM386N
2 x capacitors - 47uf
Step 1: Contact Microphone
Cut audio wire (coaxial) to desired length (I usually try for at least 1 meter).
Strip the plastic insulation from ends of the cable, twist the copper wire and tin (step 3) the ends of the two cores.
One end of the centre core of the audio cable should be soldered to the lug of the tip of the jack plug, the other end to the centre (grey) crystal of the piezo disc.
The shield (outer core) of the audio cable should be soldered to the lug of the sleeve of the jack, the other end to the edge (brass) of the piezo disc.
Step 2: Amplifier Circuit
The illustration shows the circuit from above. The copper traces of the vero board should be on the bottom.
Prepare the vero board by cutting to size (7 x 11) and cutting the tracks under the IC (LM386 amp chip) with a sharp blade or drill bit.
Solder the IC socket to the vero board, note the position of the divot. The IC will be put in place later.
Check the orientation of the capacitors to ensure they are attached to the circuit with the correct polarity. They will have a stripe on the side of the package to signify which leg is negative. This stripe relates to the grey portion of the pink circles in the illustration.
Attach the connecting wire in the positions shown in the illustration.
Solder the battery connector, take care to match the positive (red) and negative (black) wires to the correct locations.
Solder positive and negative connecting wires to the input jack and output to speaker.
Ensure common negative ground connections are made.
Put the amplifier IC in the socket. The divot in the socket and IC must be aligned as per the illustration.
N.B.: in the illustration;
pink circles with grey portion = polarised electrolytic capacitors 47uf
white wire = positive audio input
orange wire = positive audio Output
red wire = positive 9v power
black wire = negative ground
Step 3: PCB Option
I have made gerber files available which can be used to generate a stencil for etching a PCB or g-code for a CNC machine to mill a PCB. The files can be downloaded from github. The approach to populating this PCB is as in line with the rest of this instructable. Note that the symbols which show the orientation (positive and negative).
Step 4: Invitation
If you make this instrument and have recordings to share, please forward them to
Enjoy the feedback and noise.
Step 5: Enclosure
Files to 3D print an enclosure can be found here:
Designed using tinkercad: