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 -=> Roy J. Tellason said to Greg Mayman
 -=> about "POWER SUPPLY" on 01-08-04  04:06.....

 RJT> I don't even *try* to troubleshoot surface mount stuff, it's just not
 RJT> economical...

When it is a free modem, and you just *KNOW* that it should be
able to work properly... and you don't have a replacement...

 RJT> Heh.  Too bad what used to be an industry leader of sorts (as in
 RJT> "Hayes Command Set"!) is now gone...

Yes indeed :-((((
 
 GM> *  a 350w audio power amplifier

 RJT> There was a time when I'd have enjoyed that much power,  but having

That sort of thing is absolutely no use to me either.

 RJT> Motorized?  No kidding.  I'd like to have a decent _simple_ circuit
 RJT> for an electronic volume control of some sort that didn't involve the
 RJT> use of special chips,  and still haven't found it.

The advantage with a motorized one is that it is still at the
setting you left it at, next time you switch on.

 RJT> About the closest I've come to that would be an abortive experiment I
 RJT> started once that involved CMOS switches and pulse-width modulating
 RJT> chopping the signal.  It distorted horribly,  I'm pretty sure because I
 RJT> should've been using a bipolar supply and watching my signal levels
 RJT> more carefully,  but perhaps I'll get back to that somewhere along the
 RJT> line.

Yes, it could have been. I've seen some very low distortion
circuits, but most of them used specialized chips or modules.

But one that worked well used a junction-gate FET to shunt the
signal. Normally the FET is non-linear due to the amount of
signal between drain and source, but this circuit fed a selected
amount of signal back to the gate -- approximately 50% of the
amount on the drain -- which reduced the distortion by a factor
of up to 100 in some cases.

I saw this done in various ways, but the easiest was to take the
signal from the drain to an emitter follower or a unity gain
op-amp and take the feedback to the gate from the output of that
stage.

 GM> *  a 0-80A LED ammeter for cars

 RJT> No zero in the middle?  :-)  I've seen an article or two like that,

Actually it used 4 LEDs on one side and 5 on the other with the
"middle" one as the zero. The heart was a LM3914 chip, fed from
an op-amp amplifier measuring the drop on the battery earth
cable. I bought this unit as a kit from Dick Smith Electronics,
but I haven't made it up yet... doesn't that sound familaiar? 

 RJT> I've yet to get my hands on any of those "white" ones so far.

Our three main "hoppyist" suppliers in Aus all have them at
reasonable prices. And they all do mail order around the world.
Look for jaycar.com.au, altronics.com.au and
dicksmithelectronics.com.au on the internet. AFAIK they all have
on-line catalogues.
 
 GM> *  an efficient power supply for a 1W ultrabright LED "star"

 RJT> Yes?  What would that be all about?

The "star" is a 1 watt white LED. The original project in Silicon
Chip drove one with a linear constant current suppl from a 9-18v
source. This later article uses a flyback supply from two "D"
cells, and claims it will give near normal output down to 1v per
cell, if I remember correctly. The total current on new cells is
about 300-400mA which is about the same as an incandescent torch
bulb, but this thing gives a LOT more light!

 RJT> Sounds like you've got a fairly decent magazine there.  The ones here
 RJT> have all gone to hell,  pretty much,  with little of interest to me in
 RJT> them in recent years.

Silicon Chip was the "poor" relation back about 10 years or so
ago. The leaders were Electronics Australia and Electronics
Today International.

Then EA absorbed ETI. then a couple of years back, EA turned
itself into a yuppie cocktail table magazine -- "40 PAGES OF MUST
HAVE TECHNO TOYS" and the like -- and died after about 2 or 3
issues!

So SC is the only one left...

Check out their internet site at siliconchip.com.au and you will
find a table of past articles.

 RJT> I guess he wanted to build some serious machinery,  or something.  Me,
 RJT> I'll be happy if I can get something of a "tabletop"
nature going --
 RJT> something that'll mill circuit boards for me,  so I don't have to mess
 RJT> around with applying resist and etching with chemicals.

Yup, me too!
 
 GM> Bronze is usually considered as a better bearing material, and
 GM> sintered bronze bushes aren't all that hard to buy off the shelf!

 RJT> I haven't the foggiest idea where I'd go for something like that
 RJT> offhand.  I do have a bunch of these nicely smooth steel rods that came
 RJT> out of old printers,  and they did use bronze or something pretty close
 RJT> to it to slide on those,  but I don't know that I kept any of those
 RJT> bits.  It'd sure save me some trouble if I could do that sort of
 RJT> thing...

Yep. The bits that come out of photocopiers are even more
substantual than the printer bits, especially if you can find one
of the really old machines where the master page was slid back
and forth on a pretty substantual glass table!

 RJT> I think mine was around $60,  probably fairly comparable?  I got it at

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