Silicon Chip – April 2019

siliconchip.com.au Australia’s electronics magazine April 2019 43

ing the chassis-mounting type, attach
them to the board using the specified
M4 machine screws and nuts, as shown
in Fig.16.
Now all that’s left is to solder the
small electrolytics capacitors in place,
followed by the large ones. In both
cases, the longer (positive) leads must
go into the pads marked with a “+”
on the PCB.

Initial checks

Before installing the three ICs on
the preamp board, it’s a good idea to
check the supply voltages. You will
need to wire up a transformer to your

power supply, then connect the power

supply’s +15V, 0V and -15V outputs to

the relevant inputs on the main pream-

plifier PCB.

It’s safer to use a 15VAC plugpack

for testing if you don’t already have

the transformer and power supply

installed in an Earthed metal chassis.

Just connect one wire from the plug-

pack output to either of the low-volt-

age AC input terminals on the power

supply board, and the other wire to

the centre tap transformer connec-

tion point.

Plug the plugpack into a GPO and

switch it on. Now check the voltages

Making the interconnecting cables

To connect the three boards, you need to

make two IDC cables. These diagrams show

how these cables are made.

Pin 1 on the header sockets is indicated

by a small triangle in the plastic moulding

and the red stripe of the cable must always

go to these pins.

You can either crimp the IDC headers to

the cable in a vice or use an IDC crimping

tool (eg, Altronics T1540 or Jaycar TH1941).

Don’t forget to fit the locking bars to the

headers after crimping, to secure the cable

in place.

Having completed the cables, it’s a good

idea to check that they have been correctly

terminated. The best way to do this is to plug

them into the matching sockets on the PCB

assemblies and then check for continuity be-

tween the corresponding pins at either end

using a multimeter.

300mm x- 14 WAY IDC RIBBON CABLE

14-WAY CABLE EDGE STRIPE

IDC

SOCKET

14-WAY

IDC

SOCKET

200mm x0 1 -WAY IDC RIBBON CABLE

CABLE EDGE STRIPE

1- 0 WAY

IDC

SOCKET

1- 0 WAY

IDC

SOCKET

LOCATINGSPIGOTUNDER

LOCATINGSPIGOTUNDER

on pins 8 & 4 of the four 8-pin IC sock-

ets (IC1-IC4) on the preamp board; ie,

between each of these pins and the

0V (centre) terminal of CON6. You

should get readings of +15V and -15V

respectively.

Similarly, check the voltage on pin

14 of IC5’s socket. It should be between

+4.8V and +5.2V.

If these voltages are correct, switch

off and install the ICs. Note that IC1-

IC4 face one way while microcontrol-

ler IC5 faces the other way.

Remote control/switch testing

The remote control functions can

QUICK

CONNECT

M4 x 10mm

SCREW & NUT

M4 FLAT

WASHER

M4 STAR

WASHER

PC BOARD

Fig.16: here’s how the

single-ended male spade

quick connectors are

secured to the power

supply PCB. Vertical

spade terminals with

solderable pins can also

be used.

An assembled “full” power supply capable of

handling both an amplifier and this preamp. Watch the polarity of

electrolytic capacitors, diodes, LEDs and regulators.