Introduction: Squeal & Scrape (10 Acres of Sound Version)
This DIY electronic musical instrument consists of a piezo disc as a contact microphone, an amplifier and a loudspeaker. Feedback (Squeal) and overdriven textures (scrape) are easy to produce, difficult to control & fun to play with.
This instructable requires soldering.
If you need some advice about soldering, here are guides:
Work in a well-it space so you can see components and tools clearly.
Your work space should have good ventilation; a fume extractor is advised.
Have a first aid kit available in case of cuts or burns.
solder wire (lead free is preferable)
hot glue or epoxy
piezo disc / contact mic
jack plug (TS / mono)
jack socket (TS / mono)
IC (integrated circuit / chip) - LM386
IC socket (8 pin DIP)
2 x capacitors - 47uf
connecting cable (threaded/stranded or solid core)
Step 1: Piezo Disc / 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 (soldering & tinning) 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 shorter of the lugs), the other end to the centre (grey) crystal of the piezo disc.
The shield (outer sleeve) of the audio cable should be soldered to the lug of the sleeve of the jack (the longer of the lugs), the other end to the edge (brass) of the piezo disc.
Step 2: Circuit / PCB
The illustration shows the circuit board (PCB) from above.
All components should be added to meet the outlines of the components marked on the top of the board.
The capacitors have a stripe on the side of the package to signify
which leg is negative. This negative leg / stripe connects to the pad joined to the solid black portion of the symbol. The other, positive leg, connects to the pad with a white block with black outline and a + positive symbol.
Solder the IC socket to the PSB, note the position of the divot on the socket and PCB (see divot highlighted in red in the attached png), ensure they are aligned. The IC will be put in place later.
Measure the connecting wire before cutting. Use your enclosure as a guide. Make your wires long enough to connect the PCB to the jack socket, power switch and speaker then cut.
Strip approx. 1 cm of insulation from the end of the wires and tin the ends.
Attach the connecting wire in the positions shown in the illustration. Solder the black wire (negative power) of the battery connector to the PCB, cut the red wire in half (approx) solder one end from the battery connector to the centre lug of the witch, solder the rest of the red wire to connect one of the outer lugs of the switch to the PCB. 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.
Put the amplifier IC in the socket. The divot in the socket and IC must be aligned as per the illustration.
N.B.: illustration key;
rectangle block with pads, + symbol C1/C2, 47uf = polarised electrolytic capacitors
white wire = positive audio signal input
orange wire = positive audio signal output
red wire = positive 9v power
black wire = negative ground
Step 3: Enclosure
Once the circuit (amplifier) and sensor (piezo disc / contact microphone) have been assembled and tested, it is useful to have an enclosure to make the instrument easier to use, and safer to transport and store.
I have made enclosures from a range of recycled materials (cans / hi-fi equipment / plastic boxes). See example images.
Any sturdy container may be suitable. It is best to use something affordable, which can be manipulated with the tools you have available. If you are not confident with using cutting tools, find someone to ask for support.
Ensure that there is enough space inside your selected enclosure to accommodate the PCB,
speaker, panel mount hardware (input jack and power switch) and battery.
The best enclosure will afford easy access. In the video guide I use a cheap, commercially-available, plastic project enclosure (width x height x depth).
Place the instrument parts in approximate position to check there is enough space, use tape as needed.
Mark where any cuts are needed using a pencil or marker.
N.B.: Some enclosures will only need holes for input jack socket and power switch, others may require holes to let the sound of the speaker out.
Drill a small pilot hole, then increase the size of the hole using suitable sized drill bits (a stepper drill bit can be very useful here).
When the holes are drilled, remove any rough edges / burrs using a file.
Push the input jack socket and power switch into the holes you have made and attach to the enclosure, securing the hardware in place using the washer and nut provided.
Connect the contact microphone and experiment to find how may different sounds can be created.
N.B.: Don't select a metal enclosure if you don't have suitable cutting/drilling tools as this increases the chance of injury and damage to materials. STAY SAFE!
N.B.: if you use a metal enclosure (like a food tin) make sure that any exposed metal parts of the circuit are insulated (tape / glue / non-conductive material barrier) and do not touch the metal enclosure as this can lead to a short circuit, which can damage the instrument and potentially create a fire hazard. STAY SAFE!
Attached are a PDF & SVG file which were made with (free, open source software) Inkscape; a basic design to cut an enclosure from card, an example of which can be seen in the image from the first step. NB: the speaker you have been supplied may differ from the one used to base the design on - the SVG can be manipulated to create a customised enclosure to your taste. This video shows how to do some basic editing of an SVG file.
ATTENTION: It is essential to reach out to & check with your fablab technician to ensure that the SVG file is formatted to be suitable for the cutting hardware. Check that the parts you want to score & cut are set to the correct colour & stroke thickness as these vary from machine to machine.
Step 4: FINALE - Trouble Shooting / Play & Record
After making this instrument we would like to have two follow up sessions:
The first session is a trouble shooting - participants can send requests for assistance and receive feedback on their build.
The second session is playing and recording - we will play the devices together; to share techniques and approaches which produce enjoyable listening results.
During this second session participants are encouraged to record themselves playing (audio & video using a smartphone) and send the recordings to be edited into a showcase video which will be broadcast before live streamed performances as part of the 10 Acres of Sound
Enjoy the feedback and noise.