54 December 2014
bottom were a bit narrow, but were easy enough to work
with using a fine point on the soldering iron.
With both amplifier modules built, it was time to
move on to the power supply.
The power supply board is shared with a few other
Boxed Kit Amps projects, so has some extra pads that
aren’t meant to be populated in this version of the kit. It’s
a straightforward power supply — a toroidal transformer
feeding a bridge rectifier, filtered by 4,700 µF capacitors to
form a bipolar power supply. One nice touch are the LEDs
across the filter caps as bleeders. They could be replaced
by a resistor if you don’t want another light source in the
First power-up and no smoke! The LEDS are cool
sitting there on, and the power switch lights up when
turned on, too. A quick check of the voltages shows
they’re within spec. The power supply might benefit from
a little better voltage regulation — the positive and
Figure 12. Mounting the bridge rectifier, terminals, and LEDs.
Figure 14. First power supply test.
Figure 16. Laying out the components.
Figure 13. Adding the transformer.
Figure 15. Measuring the unloaded output voltage.