negative rails are close, but are not quite perfectly
Finally, it was time to hook everything together. I
started staging the boards roughly where they mount
inside the enclosure and hooking it all together. Wiring the
boards together was a bit tedious, but uneventful. I did
find the holes for the wires to be a bit small — especially
the speaker output leads. It took several tries to remove
the right number of individual strands from the bundle
before they seated nicely, but otherwise it wasn’t too bad.
On the power supply board, a screw-down terminal
block holds the DC power wires. On the amp modules,
those wires are soldered in. Audio input is a screw-down
terminal, and speaker outputs are soldered in place.
By now, you’re thinking “all this plastic, it’s not
shielded at all — how is it going to protect against noise
and interference?” And, you’d be right. It is all plastic, but
luckily interference and noise aren’t an issue as the signal
path is fully shielded — from the input jacks through coax
to the volume control with a grounded metal body, and
through more shielded coax to the amplifier input.
Luckily, there was no smoke on the fully assembled
test run, either. I did do a couple of tests. First, with no
input signal, I turned the volume to max and listened for
white noise in the speakers. It was nearly completely silent
— very nicely done. Then, I hooked it up to my meters. I
got about 12W with low to virtually no distortion into an
8 ohm load (less than 0.06% THD), 15W with moderate
distortion (<2% THD), and past 15W up through 25W
measured power with distortion starting about 30%.
With confirmation it was working well, I zip-tied and
bolted everything together. Some of my wire routing was
a bit longer than I liked, but with the fully shielded audio
path, I wasn’t too worried about an extra inch or so in a
couple of places.
The case itself is beautiful. It’s a laser cut piece of
transparent blue acrylic with a very interesting etching
pattern to let it wrap around and form rounded corners.
The entire main section of the case is made of a single
piece of acrylic, with separate front and rear panels with
laser cut holes for the inputs and outputs. It came with a
Figure 18. First full system test. Figure 17. Mounting the hardware.
Figure 20. Completed amplifier, rear. Figure 19. Completed amplifier, front.
December 2014 55