•
While the MJL21193/94 transistors
from ON Semiconductor are recommended, they are now obsolete and
difficult to get. We recommend the ON
Semiconductor NJW21193/94 transistors instead.
You could use MJL1302/MJL3281.
As you mention, they have a higher
cut off frequency. This might or might
not be a problem.
They may give better performance,
but it’s also possible that the amplifiers
could oscillate. If you find the DC fuses
are blowing for no reason, try increasing the value of the 100pF 500V compensation capacitor. However, as that
value is quite high, it should be OK.
According to the circuit, you need
seven of each type of transistor, regardless of which types you use.
Power supply cable
stripe polarity
I use figure-8 speaker cable (eg,
Jaycar WB1703) in many projects.
Should the black stripe for polarity
identification be used for positive or
negative?
I originally thought black indicates
negative, but then I noticed that most
plugpacks have the striped side of
the wire indicating positive. Now I’m
thinking that as positive is the wire I
want to be identified, perhaps I should
always use the black striped wire for
positive.
I use the wire for motors and Arduino projects, but if anyone was connecting speaker wire to the black and red
terminals on a speaker box, surely the
wire with the black stripe would go to
the black terminal. Is there a standard
for this? (J. B., Benalla, Vic)
•
If you have red and black wires,
then usually red would be positive
and black would be negative. But it’s
a bit more tricky when you have a
stripe. Sometimes you have a white
stripe, sometimes a red stripe and
sometimes a black stripe (and possibly other colours).
Usually, the stripe is used to indicate positive, but that certainly is confusing when the stripe is black.
Ultimately, it doesn’t matter as long
as you are consistent so that there is
no confusion. As you say, plugpacks
tend to use the stripe for positive
(usually a white stripe, though), so
it would make sense to follow that
convention.
Probably the best solution would be
to use Jaycar Cat WH3057, WH3087
or similar cable which has red and
black insulation for the two wires in
the cable.
Flashing lights wanted
for model railway
I am trying to find a railway crossing flashing light kit, or at least a PCB
for it. I am sure I have seen something
like it in past magazine issues. I have
searched your site without success.
Could someone point me in the right
direction? (P. C., via email)
• We published a two-lamp flasher
circuit (January 1998; siliconchip.
com.au/Article/4748). You can download its PCB pattern from the following page: siliconchip.com.au/
Shop/10/2362
Jaycar also sells a kit for that project, Cat KJ8070. This design runs
from 12V and so is suitable for 12V
SC
lamps.
Advertising Index
Altronics...............................89-92
Ampec Technologies................. 19
Dave Thompson...................... 111
Digi-Key Electronics.................... 3
Emona Instruments................. 101
Jaycar............................ IFC,53-60
Keith Rippon Kit Assembly...... 111
LD Electronics......................... 111
LEDsales................................. 111
Microchip Technology.............. IBC
Mouser Electronics...................... 7
Ocean Controls......................... 39
Rohde & Schwarz.................. OBC
SC Micromite BackPack............ 47
Silicon Chip Binders............... 106
Silicon Chip PDFs on USB..... 111
Silicon Chip Shop.................. 100
Silicon Chip Subscriptions....... 88
The Loudspeaker Kit.com......... 99
Tronixlabs................................ 111
Vintage Radio Repairs............ 111
Wagner Electronics..................... 5
Notes & Errata
Balanced Input Attenuator for the USB SuperCodec, November-December 2020: the photo shown halfway down the lefthand column on page 71 of the December 2020 issue, showing the wiring to the power connector, is incorrect. The positive
(red) wire should be shown going to the bottom-most pin in the socket, with the black (negative) wire to the top. Also, in the
circuit diagram on pages 50 & 51 of the November 2020 issue, the centre (ground) pin of CON3 at upper right should only be
connected to the junction of the two zener diodes, the negative end of the 100µF capacitor next to switch S1 and the negative
ends of all relay coils. The junction between this ground and the other grounds in the circuit is on the main SuperCodec board.
Two LED Christmas Stars, November 2020: in the parts lists on page 41, there is no such part as a 75HC595. It should read
74HC595 instead.
D1 Mini LCD BackPack with WiFi, October 2020: in the circuit diagram (Fig.1), the connections to pins 7 & 8 on the LCD
module via CON1 are swapped. The drain of Q1 should go to pin 8 (LED) while pin 7 is the display SCK line and also connects
to pin 10 on the LCD module and on to the D5 pin of MOD1.
The February 2021 issue is due on sale in newsagents by Thursday, January 28th. Expect postal delivery of
subscription copies in Australia between January 27th and February 12th.
112
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
