Advertising Index
AEE ElectroneX........................... 34
Altronics.................................75-78
Analog Devices............................. 9
Dave Thompson........................ 111
Digi-Key Electronics...................... 3
Emona Instruments.................. IBC
Hare & Forbes............................... 5
Jaycar.............................. IFC,53-60
Keith Rippon Kit Assembly....... 111
Lazer Security........................... 111
LD Electronics........................... 111
LEDsales................................... 111
Microchip Technology.............OBC
Mouser Electronics....................... 7
Ocean Controls........................... 10
PMD Way................................... 111
SC SMD Test Tweezers............ 109
Silicon Chip Shop............ 106-107
Silvertone Electronics................. 65
Switchmode Power Supplies..... 11
The Loudspeaker Kit.com.......... 67
Tronixlabs.................................. 111
Vintage Radio Repairs.............. 111
Wagner Electronics....................... 8
around Q1-Q4 would help to diagnose this fault further, but given that
they are inexpensive devices that are
relatively easy to replace, if you can’t
find a soldering problem or component
value error in that area, you could just
replace all four.
wide. This can also damage the ignition coil that could arc over internally
and short out the windings. That fault
is more difficult to check; the easiest
method is to swap the coil and see if
that fixes it (after checking the IGBT
using a resistance meter).
Jacob won’t climb his
ladder anymore
Modifying EA Active
Crossover frequencies
We bought our son a Jacob’s Ladder kit for Christmas. We separately
bought the coil recommended in this
kit.
Upon original completion, the kit
worked fine. While using it, it stopped
working and has not worked since.
We asked the retailer about this, and
they agreed that we had built the kit
correctly. Still, they were concerned
by the age of the kit on their shelves
(which they stated may have been
there for many years) and the possibility that components may have
dried out over this period, leading to
the failure.
Do you have any experience with
regards to which components regularly fail? (G. D., Redcliffe, Qld)
● Electronic components sitting on a
shelf should not fail after less than ten
years. The only parts that are likely to
age significantly are electrolytic capacitors, and we have plenty of 30-plusyear-old electros that are still fine.
Modern electrolyte formulas handle
ageing much better than much older
devices.
The semiconductors, resistors etc
will definitely still work.
Check fuse F1, which may have
blown. The most likely failure is
the IGBT (Q1). Usually, when these
fail, they end up with a short circuit
between the gate and collector (left
and centre pins) or the collector and
emitter (centre and right pins).
The IGBT is most likely to be damaged due to the spark gap being too
I recently came across several Twoway Electronic Crossover kits I started
assembling about 10 years ago that I
would like to complete. They were
sold by Altronics, Cat K5570.
The problem is that I have lost the
instructions that came with them.
Also, they were initially designed for
crossing between mid-high and high
elements. I would like to use them for
crossing over at 100Hz. Can you suggest the component values required for
sub-bass applications? (M. O., Croydon, NSW)
● Those kits are based on the Active
Crossover for 2-Way Speaker Systems project from Electronics Australia, May 1992. A scan of that article is available for purchase from
our website (siliconchip.com.au/
Shop/15/6072).
To change the crossover to 100Hz,
the component values can be scaled
using the original crossover frequency
versus resistor value tables. You can
change the 2043Hz value to 100Hz
by multiplying the resistor values by
10 and the C2-C7 capacitor values by
2.043.
So R2-R4, originally 39kW, become
390kW and R5-R7 become 470kW
(from 47kW). The original 2.2nF
capacitors can be 3.9nF in parallel
with 560pF (4.46nF total, within
1% of the required value of 4.49nF).
Capacitor tolerance (typically at least
±5%) will be the main cause of frequency shifts from the required crossover frequency.
SC
Notes & Errata
Vintage Radio, February 2022: the 100nF capacitor directly below the 6K8M valve in Fig.8 should connect to the GND rail instead
of the AGC line. In that same figure, there’s a 33μF 600V HT filter capacitor missing from the 250V rail to GND.
USB Cable Tester, November & December 2021: in the circuit diagram, Fig.1 on page 30 of the November issue, the numbers
for pins 8 and 10 on IC1 are swapped. Pin ANE2/RE2 connecting to USBU-GND via a resistor should be pin 10, while pin ANE0/
RE0, connecting to USBU-ID via a resistor, is actually pin 8.
The April 2022 issue is due on sale in newsagents by Monday, March 28th. Expect postal delivery of subscription copies
in Australia between March 25th and April 15th.
112
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
