72 Silicon chip Australia’s electronics magazine siliconchip.com.au
faces in the direction shown on the overlay diagrams, ie,
towards the top or left edge of the board.
Now install the 1W resistor(s) and a socket for IC1, assum-
ing you’re using one. You can then mount the two 100pF
capacitors and single 100nF capacitor. None of these are
polarised.
Follow with the terminal block, if you’re going to be us-
ing it, ensuring that it is pushed down flat onto the board
and that its wire entry holes face the nearest edge.
You can use a 3-way terminal block for all four config-
urations, however, with two of the configurations, only a
2-way block is required as shown in Figs.5 & 8.
If using a two-way block, make sure to solder it to the
right pair of pads.
Now fit the electrolytic capacitors. These are polarised
and must be orientated correctly. The longer (+) wires go
into the pads marked with a “+” on the PCB, towards the
top edge of the board. The striped side of the can shows
the negative terminal, so the stripes should all face towards
the bottom edge.
There are three different types of electrolytic capacitors
used, so don’t get them mixed up.
Finally, fit the RCA terminals and DC socket (if required).
In each case, make sure the connector is pushed down ful-
ly onto the PCB and lined up nicely with the PCB edge be-
fore soldering its pins. Be generous with the solder as these
pins are quite large.Testing
Before mounting it, it’s a good idea to test the unit. If you’ve
fitted a socket for IC1, you can leave IC1 out until you have
verified that the power supply is working OK.
It’s best to test the unit with the same type of supply that
you will eventually be using, however, if you intend to use
a centre-tapped transformer or split supply, you could use
a 9-16V AC plugpack for initial testing.
Apply power and measure the voltage between GND (eg,
the RCA connector shells) and pin 8 of IC1 (or its socket).
If using an AC supply, you should get a reading of around
+16V DC, or perhaps slightly lower if your AC supply is be-
low 12V. Similarly, pin 4 of IC1 should be at around -16V
DC. Pin 5 should be close to 0V.
If you’re using a DC split supply, you should measure
voltages at pins 8 & 4 of IC1 that are around 0.7V less than
the applied voltages, while pin 5 should be close to 0V. And
if using a single-ended DC supply, pin 8 should be around
0.7V less than your applied DC voltage, while pin 4 should
read 0V and pin 5 should be almost exactly half the read-
ing at pin 8.
If you get readings that are significantly different from
those described above, switch off power and check your
board carefully. Things to look out for are bad solder joints,
incorrectly orientated components or components that are
in the wrong location.
If the power supply checks out, switch off power, short
out pins 4 & 8 of IC1’s socket briefly (to discharge the capaci-
tors) and then insert IC1 in its socket. Re-apply power and
apply a signal to CON1, from a Blu-ray player, iPod, mobile
phone, PC or whatever’s convenient. Connect CON2 to the
input of an amplifier with its volume set to minimum, then
slowly ramp its volume up.
You should hear the input signal being reproduced clean-
ly. Disconnect CON2 from the amplifier and connect CON3
instead. You should again hear the input signal being re-
produced cleanly (the fact that its phase is inverted will
not be audible).
You can now do a final test, with CON2 hooked up to
one amplifier input and CON3 to another, and the speakers
connected across the amplifier outputs, as shown in Fig.1.
Again, you should hear the signal loud and clear. OnlyFig.9: if you’re mounting it in a UB5 Jiffy box, here’s where
to drill the holes required in the sides and base. The PCB is
attached to the base using untapped spacers and machine
screws (see parts list & text).
Fig.10: same-size label which fits the UB5 Jiffy box. You
can photocopy this or download it from siliconchip.com.
au/shop/11/4972