12 Silicon chip Australia’s electronics magazine siliconchip.com.au
that government’s program was crystal
clear. Nothing bad could be said that
day about the NBN.
Yet the program to replace a copper
voice network with a fibre data net-
work over which we will carry voice
is a huge and revolutionary program.
To attempt to replace in just 15 years
what has taken almost 150 years to
evolve is ‘crazy brave’.
One of the costs of doing it is the loss
of the ‘baked in’ emergency phone sys-
tem. If only we could have reasoned
debates about national issues, and so
have most of us understand much of
this revolutionary program.
While the whole NBN system does
away with the fail-safe phone system,
your correspondent attaches his ire
to the HFC variety. Paradoxically, the
HFC system does provide a solid cop-
per connection into the home, and in
theory, at least, could provide its own
power supply.
That will never be done, of course,
and even with HFC, we have no choice
now but to find alternative strategies
for emergencies. Relying on mobile
phone technology is not an intelligent
emergency strategy.
Max Williams,
Ringwood North, Vic.
Comment: we did not add a footnote
to that letter because the implications
should be clear to anyone reading that
letter (and indeed, this one).Combining two preamp designs
I have recently finished building
the Studio Series Stereo Preamplifier
from October 2005 (siliconchip.com.
au/Article/3203).
I modified the circuit to use NE
op amps instead of OPA2134s, as they
are easier to get and cheaper, with
similar performance. I also changed
the component values around them to
those specified for the Ultra-LD Stereo
Preamplifier, November & December
2011 (siliconchip.com.au/Series/34).
The reason I didn’t simply build
the 2011 design is that I need more
than three stereo inputs. The 2005
board suited my requirements, with
six inputs.
I did not fit the 1MW resistors at the
input to the preamp, and I am fitting
6.8kW resistors between the wiper and
ground ends of the 10kW logarithmic
volume control potentiometer (VR1). I
calculate that this will provide a suit-
ably low impedance to the input of the
second op amp, in line with your 2011article’s tweaking section. To make
all these changes, I had to cut several
tracks on the PCB.
I am building two of these preamp-
lifiers. The first is to use with a modi-
fied Hifi Stereo Headphone Amplifier
(September-October 2011; siliconchip.
com.au/Series/32). To simplify power
supply arrangements, the headphone
amp will be run off a ±15V supply.
The second preamp is used in con-
junction with powered studio monitor
speakers. It will be interesting to see
how the preamps perform once both
projects are up and running.
Many thanks for a great magazine.
My copies date back to 2002. I hope
that your interesting and well ex-
plained designs can continue and you
are not forced to restrict/dumb down
projects to plug-pack only operation.
I fear this may be the case after read-
ing your April 2019 editorial on com-
plaints about publishing mains-pow-
ered designs.
Richard Kerr,
Cessnock, NSW.
Comment: the only real benefit of us-
ing OPA2134 JFET-input op amps in
the Studio-series Preamp over the
good old NE5532s is that they allow
the relatively high (1MW) input imped-
ance, but this is not required for most
equipment.Suggestions for UPS battery
replacement
I saw Peter Allica’s request in the
Mailbag pages of the March issue, for
help with information on Datasaver
UPSes, as he was planning to upgrade
them to use modern batteries.
Googling “Datasaver” yields a lot of
irrelevant hits, so that’s not going to be
an easy avenue. I tried a reverse lookup
of the old phone number, it’s now in
Mount Nelson and looks residential.
So we’ve struck out there.
But, a few days ago, I was looking at
Jaycar’s latest flyers online. They have
just released a range of LiFePO 4 batter-
ies they say can be used as a straight
replacement for lead-acid batteries.
I have no additional information on
these products apart from what’s in
Jaycar’s flyers and website where a
brochure can be downloaded.
I am in a similar boat to Peter. It ap-
pears that my UPS needs its third SLA
battery. It died about the time of the
bushfire scare here. I am trying to find
out whether I could put one of these
new LiFePO 4 batteries into my UPS;For Wholesale prices
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