92 Silicon chip Australia’s electronics magazine siliconchip.com.au... Screen17: the
crossover mode screen.
By default, it’s Stereo, as
shown here, but you can
change it to...Screen18: Bridge mode,
where the second output
is an inverted version of
the first output, for using
two mono amps (or one
stereo amp) to drive a
speaker in bridge mode.
Pressing S2 again...Screen19: cycles through
the same set of options
for the next band,
starting with the lower
-3dB point adjustment
and then all the different
settings and bands until
it loops back to Band 1.
Screen20: here’s the
main menu again,
and this time we have
selected the Parametric
settings. Pressing S2
takes us to...Screen21: this screen
lets you choose which
parametric equaliser
band to adjust. There
are four bands which
apply to both channels,
plus two that only
apply to each of the two
individual channels....Screen22: The rotary
encoder lets you select
any of these eight
equaliser bands. Here
we have selected the first
band which applies only
to Channel 1, and here...
Screen23: we have
selected the second band
which applies only to
Channel 2. Pressing S2
on any of these options
takes you to...Screen24: this screen,
which lets you switch
on or off each equaliser
band. Pressing S2 again
takes you to...to apply neutral-cure silicone sealant in these areas so that
they are not a shock hazard if you operate the device with
the case open, during testing.
It is somewhat easier to drill a hole to suit a wired-in
mains cable, and that is a valid approach; just make sure
you fit a proper ‘safety’ fuseholder wired in series with
the active lead, and that you provide adequate clamping
to ensure the mains cord can’t be accidentally pulled out,
even if the unit is dropped.
The best way to do this is either using a cord grip grom-
met (although this does require a properly profiled hole to
be made) or an appropriately sized cable gland. If using a
cable gland, it’s best to fit the part which tightens up around
the cable on the inside of the case, so it can’t be loosened
from the outside. Alternatively, apply superglue (cyanoacr-
ylate) to the threads before tightening it up.
Another thing that’s necessary if you are using a mains
power supply in a metal case is to properly Earth the case.
Run a short green/yellow striped Earth wire (stripped from
a section of 10A-rated mains cable) directly from the mains
input socket to a chassis-mounting eyelet or spade lug. If
the case is painted, scrape the paint away around the lug
mounting point.
Use the largest diameter screw possible to attach this
lug, along with shakeproof washers and two nuts. If using
a captive mains cord, simply separate its Earth wire and
run it to this chassis Earth lug. You do not need to make
an Earth connection anywhere else in the device.
You also need to ensure that there is good electrical con-
tinuity between the various case panels when the case is
assembled. This may require removing some paint where
the panels are screwed together, or otherwise attached.
Verify that you have a low resistance between any ex-
posed metal on the case and the mains Earth pin before
powering the unit up.Mounting the modules
Once you have made the holes in the rear panel and at-
tached and wired up any required power supply compo-
nents, you can mark out the mounting hole positions for
the power supply board, CPU board, ADC board and DAC
boards. Drill these to 3mm, deburr, then attach the modules
using machine screws and tapped spacers. You can then
wire them back up, as you did during the testing.
That just leaves the LCD and front panel control module
to mount. You need to make a rectangular cutout 82mm
wide and 52mm tall in the front panel for the LCD screen
to fit through. (See Fig.22).
Make sure it’s centred vertically on the panel, and at
least 5mm from any protrusions on either side, as the LCD
board is slightly larger than the screen (92mm x 70mm).
You can draw the required outline on the panel and
then cut it out using a rotary cutting tool like a Dremel. Or
you could drill a hole and then use a nibbling tool. Either
way, file the edges smooth and make sure that the panel
fits, then mark out and drill the four 3mm corner mount-
ing holes. You can then attach the panel using 16mm M3
machine screws, nuts and washers.
Extra nuts and/or washers can be used to space the LCD
board out from the panel (see the photo on page 86).
Finally, drill the holes for the rotary encoder, pushbut-
tons and mounting screws as shown in Fig.21(a). This can
be used as a template, but make sure it’s far enough away