Advertising Index
Altronics.................................19-22
Blackmagic Design..................... 37
Dave Thompson........................ 103
Emona Instruments.................. IBC
Hare & Forbes............................... 7
Icom Australia............................. 10
Jaycar............................. IFC, 30-33
Keith Rippon Kit Assembly....... 103
Lazer Security........................... 103
LD Electronics........................... 103
LEDsales................................... 103
Microchip Technology.............OBC
Mouser Electronics....................... 3
OurPCB Australia.......................... 6
PCBWay......................................... 5
PMD Way................................... 103
Rohde & Schwarz........................ 97
SC Micromite Explore-40......... 103
SC PIC Programming Adaptor... 72
Silicon Chip Back Issues..... 45, 88
Silicon Chip Battery Checker.... 66
Silicon Chip PDFs on USB......... 57
Silicon Chip Shop...........90, 98-99
Silicon Chip Songbird................ 51
Silicon Chip Subscriptions........ 73
The Loudspeaker Kit.com.......... 89
Wagner Electronics....................... 9
Errata and on-sale date
Vintage Radio – Emerson 888,
May 2025: Ian Batty quoted his
favourite “weak signal” station
as 3WV at Warrnambool. Fellow
HRSA member Bob Forbes
informed him that the station at
Warrnambool is actually 3WL
(1602kHz), ABC South Western
Victoria. His reference is actually
3WV (594kHz), ABC Radio
Wimmera at Horsham, around
300km from Rosebud.
Next Issue: the September 2025
issue is due on sale in newsagents
by Thursday, August 28th. Expect
postal delivery of subscription
copies in Australia between August
27th and September 12th.
104
Silicon Chip
It seems like the plugpack power
supply is not delivering power or there
is a short circuit or something drawing a lot of current in the circuit. Start
by checking the plugpack output. Is it
capable of delivering 2A? If it seems
OK, perhaps there is a component
drawing extra current. It would get
hotter than expected.
The fact that the power LED flashes
suggests that the plugpack is switching
on and off, and is possibly overloaded.
We recommend using an Altronics
M8945A (15V DC, 2.4A) or M8945B
(15V DC, 3.5A) plugpack to power the
Precision Turntable Driver. Jaycar’s
MP3492 could also be used, although
its 2A rating is only just high enough.
As for the inability to reduce the
speed, we think it is likely a fault with
the button or its wiring.
Editor’s note: the reader later replied
that the plugpack was at fault.
RIAA Preamplifier
wanted
I have been asked to restore a 1950s
chest-type valve radiogram that has
great sentimental significance to its
owner. Unfortunately, the existing Collaro record changer looks to be beyond
help, with perished rubber parts. The
only solution is to retrofit a newer turntable/record changer.
I envisage using something like a
later model Garrard fitted with a magnetic cartridge. The radiogram won’t
have sufficient audio gain to be driven
directly from a magnetic cartridge, but
I can easily add a solid state preamplifier, hidden inside the cabinet of the
radiogram.
Have you published a design for
a mono (or stereo) RIAA magnetic
phono preamp that can provide up to
300-400mV output? If so, do you have
PCBs available for it?
The equalisation curves are different between LPs and 78s. I don’t know
what the record playing expectations
of the radiogram’s owner are as yet.
I am assuming that 78 magnetic cartridges are still available, should the
owner plan on playing 78 records. I
am aware that the output level of the
preamp depends on the output level
of the cartridge.
Assuming there is a suitable design,
can I tweak the preamp’s output level
by changing the amount of feedback on
the preamp’s IC, or is the feedback loop
entirely dedicated to the equalisation
Australia's electronics magazine
components? Also, what are its power
supply requirements? (P. W., Auckland, New Zealand)
● We published a Magnetic Cartridge Preamplifier in August 2006
(“Build A Magnetic Cartridge Preamplifier”; siliconchip.au/Article/2740).
This is a stereo preamplifier and
its gain should be suitable for your
required output level. This level
depends upon the cartridge signal output with record groove modulation.
The PCB is available from our
Online Shop (siliconchip.com.au/
Shop/8/860). You can adjust the gain
by changing the components. We
also have a SPICE simulation file that
can be used to check the response
if changes are made. Changes to the
gain shouldn’t be necessary normally
unless a low output cartridge is used,
such as a moving coil type.
It can run from a 12V AC 250mA
plugpack. The circuitry has onboard
12V regulators to provide the required
±12V rails.
How to make a whistle
filter
I am trying to build one of your old
projects, but it uses parts that are no
longer available. Can you tell me how
to make a 9kHz whistle filter coil and
a 15.625kHz whistle filter coil? (W. O.,
Miller, NSW)
● The 9kHz notch filter would be for
an AM receiver, while the 15.625kHz
filter would be to remove the horizontal scan frequency from an analog CRT
TV. The components used can include
an inductance, a capacitance and a
resistance, or simply resistors and
capacitors, with or without op amps.
For passive filters, go to siliconchip.
au/link/ac79 and scroll down to RLC
notch filter. That will give you the
details and equation to relate the notch
frequency to the component values.
You can work out the details for
winding an air-cored inductor, if
required, using the online calculator
at siliconchip.au/link/ac77
Or, for a ferrite-cored inductor, use
the online calculator at siliconchip.au/
link/ac78 (you will need to know the
AL value of the ferrite core).
Active filters can be easier to build
than passive filters using an inductor, since these can just use resistors
and capacitors, as described on Rod
Elliott’s website at https://sound-au.
SC
com/articles/notch-filters.htm
siliconchip.com.au
