MUSIC
¼" mono jack
Switch
Sleeve
Tip
Volume 1kΩ
Sleeve
10Ω
AB
Speaker ground
Hot output (+)
C
Fig. A: There are many different styles of ¼" and
1"
switching audio jacks available. Fig. B: One common
connection configuration for a switching audio jack.
If your jack varies significantly from this layout, look
for a spec sheet online. Fig. C: Open the device and find
the speaker. (For safekeeping you can stick the screws
to the speaker magnet.)
MATERIALS AND TOOLS
3. Identify the speaker ground
and hot signal lines.
Two wires connect the speaker to the circuit board:
the hot signal that creates the fluctuating sound
wave and the stable speaker ground that estab-lishes the signal amplitude. The ground attaches
to the power supply (the negative contact in most
pro audio gear, but toys can run either way). Once
you’ve identified one wire, you know what the other
one is, and you can use some tape to mark them
both on your board. Here are clues to check for:
WARNING: Unless you’re experienced with
electronics, you should only work on circuits
that are battery-powered or use a very low-amperage power supply (50mA or so). Poking
around inside high-voltage and/or high-current
circuits can be fatal.
Audio toy, mono (single speaker) battery-powered
or very low amperage
Potentiometer and matching knob A 1kΩ or 10kΩ
pot usually works, like item #271-215 from
RadioShack ($3,
radioshack.com). Some people
prefer audio taper (logarithmic) pots, but regular
linear pots work fine, too.
Switching audio jack, normally closed (NC) Choose a
¼" jack for guitar cable or
1" ( 3.5mm) for mini/
headphone plugs.
Wire, stranded, 22 gauge
3' total is plenty. Scrounge
from anywhere, or RadioShack #278-1224 ($7).
10Ω resistor (optional) Attaches across the outer
legs of your potentiometer if your output is
distorted. RadioShack #271-013 ($1 for 5).
Soldering iron and solder
Drill or Dremel rotary tool
Continuity tester, ohmmeter, or multimeter
Screwdriver, pliers, masking tape, and pencil
Follow the leads to the power supply. »
Use a continuity tester. » Most multimeters have
a continuity setting marked with an image of a
speaker or sound waves. Disconnect the speaker,
touch one meter probe to the positive or negative
power supply, and then touch the other probe
consecutively to the speaker’s contact points on
the board. The speaker contact with zero resistance to either power contact is ground.
124 Make: Volume
24
