74 Silicon chip Australia’s electronics magazine siliconchip.com.au
machine screws up through the bottom
of the box and set it on a flat surface
so they won’t fall out. Next, drop the
6-7mm untapped spacers over the screw
shafts and lower the board into the case.
To do this, first insert the RCA socket
barrels through the holes in the case,
then drop the opposite edge down
into the box. You may have to push a
little, getting the box to flex, to get it
into place. Once all four screw shafts
are through the holes on the board, use
thin-nosed pliers to hold a nut on top
and do up each screw one at a time.
This is a bit tricky since initially,
the other three screws will be loose, so
you can’t just lift up the box, or they
will fall out.
We did it by sliding one corner of
the box over the edge of the desk while
holding that screw so it couldn’t fall out,
then carefully rotating it so it threaded
onto the nut, then moving on to another
corner. Each nut you thread will make
it easier to do the next one.
Alternatively, you could use Blu-
tack, silicone sealant or some other
Fig.11: this is how you can use an SPDT switch to allow an amplifier to be easily reconfigured as either stereo or bridged
mono. This makes a lot of sense when building the unit into an amplifier; when building it separately into a box, you can
easily achieve the same result by re-plugging cables. The switch is shown here as a toggle type, but it could be a push-on/
push-off, slide or even rotary switched.
type of glue to temporarily hold the un-
tapped spacers over the holes in the box
while you insert and do up the screws.
Do them all up tight, then put the lid
on the box and affix the label. The art-
work for the label can be downloaded
from the SILICON CHIP website in PDF
format and then printed out.
For information on how to make a
label, see: http://www.siliconchip.com.au/
Help/FrontPanelsMounting it in an amplifier
If you want to integrate it into an
amplifier, this is quite easy. You can
use longer tapped Nylon spacers and
mount it to the bottom of the chassis
using eight short M3 machine screws.
It’s then just a matter of wiring up
the AC or DC power supply connec-
tions to CON5 and connecting the au-
dio signals using cables terminated with
RCA plugs.
You could make these by simply buy-
ing two RCA-to-RCA plug cables and
then cutting them in half and stripping
off the insulation.Fig.11 shows how you can use a
standard SPDT switch (toggle, latching
pushbutton, rotary or slide) to allow
the amplifier to be reconfigured as ei-
ther stereo or bridged mono at any time.Using it
If you’ve built the unit into an ampli-
fier with the switch as described above,
you can apply a stereo signal to the am-
plifier’s left and right input channels,
with the switch in the STEREO posi-
tion, and it will operate normally as a
stereo amplifier.
Or apply a single signal to the left
input channel and put the switch in
the MONO position, then connect a
speaker wired as in Fig.7 for the bridged
mono mode.
Or if you’ve built the unit into a Jif-
fy box, connect it to a stereo amplifier
or pair of mono amplifiers as shown in
Fig.1, for mono mode.
If you want to use the stereo amplifier
in stereo mode, merely disconnect the
unit and wire up the inputs and speak-
ers as you usually would.Here’s
what it looks
like mounted in
the UB5 Jiffy box (sans
lid!), drilled as shown in Fig.9.
If CON5 is used, access holes would
also be needed on that side.And here
is the finished
device, complete with
a panel (see text). The beauty
of this design is that no extra holes
are required in the panel itself –
they’re all in the box sides.SC