Dual mono 20W class-A amplifier wanted
Could you do a follow up article to the Class-A amplifier with
details to make it into a dual mono design? I think that would interest a lot of
readers, as that is what I intend on doing.
The only problem I have is that the specified transformer is
$90. So that makes $180 (one per channel). Could you recommend any other
toroidal transformers that will do the job?
Point Cook, Vic.
Comment: the extra power transformer will not be your only
added expense. At the very least, you will need two power supplies, two chassis
and two loudspeaker protectors. Harbuch Electronics (02 9476 5854) may be able
to supply suitable transformers.
Fair go for
As a long-time reader of your magazine from the first issue, I
write again for you to reconsider your position on publishing a good tube
amplifier design based on the classic Mullard principles.
From "never ever a valve amplifier project stance" at
SILICON CHIP we have had everything but,
as I recall a project to convert computer power supplies to use in valve
projects, a 12AX7 preamplifier, the Mudlark single-ended valve amplifier, a
Nixie clock and even a 3-valve radio.
Please go the whole way and give us a valve amplifier project.
You may be pleasantly surprised how popular this would be. Not all of us want to
build Class-A amplifiers and many of us would like to express our individuality
and not purchase mass-produced commercial items.
Don’t forget: nothing too exotic, eg, EL34s, 12AX7, 12AU7,
20-30W per side, negative feedback and on the roll-your-own principle.
Project to erase watermark logos
I have been reading the ABC TV forum which has lots of negative
views on the use of watermarks in general and the new ABC watermark logos in
particular. Australian free-to-air channels are using them now and they are
truly annoying to a significant percentage of viewers.
Nobody is listening, it seems and it’s time to act. Watch less
TV is one solution. Another is to tape a piece of grey paper to the screen! Yet
another is to blot the watermark out electronically.
How about a device that takes in the signal (SCART, CVBS, etc)
and inserts a rectangle in the picture, then outputs the modified video signal
to the TV? Two front-panel pots could set the position and its hue and luminance
could be an average of the picture composition in the area near the
This could be your most popular project! It would be pretty
easy too, with an LM1881 sync separator, some line counters, a monostable or
two, a video mixer, etc.
P. K., via email.
Comment: watermark logos are very annoying but there is no easy
way to remove them and your suggested cure might be more obvious than the logo.
Some stations smear over the logos of overseas networks and then place their own
over them (eg, SBS on their news bulletins).
It will also be problematic to do it with component video
signals and probably impossible with HDMI signals from HD set-top boxes. We will
have a look at the idea though.
We think that your idea of watching less TV may be the best plan and the one
that networks would be the most sensitive to.