Wiring shown overleaf will disconnect the battery when you remove
the jack plug from the input, and also when a DC plug is inserted.
Snap the little metal tag off the pots to mount them flush in the box.
You should use some kind of heat sink on the legs of the diode and
transistors when soldering. They aren’t keen on heat. Any more
than 3-4 seconds of iron and they’re toast.
I’ve incorporated the Current Limiting Resistor for the LED into the
board for your pleasure.
Once its all built and hooked up to test (see next page), adjust the
trimmer. You’re aiming to have the voltage at the Drain of Q5 at
around 50% of the supply voltage. Note - the diode will drop the
voltage going to the circuit by around 1V.
So.. get your multimeter and hook it up to a convenient GND point.
Measure the voltage at the negative side of D1
(A)
. Now, measure
the voltage at the Drain of Q5
(D)
and adjust the trimmer until you
hit around 50% of
(A)
’s voltage. That’s your starting point. Now fine
tune by ear until its perfect for you.
1 2
3
D
A
