Speaking of Merlins

[Tony Clark]

>         If memory serves correct, zeners drift with temperature. Is this so
> and by how much? The point Paul made about using an external reference on a
> 723 is not lost on me at the moment. I'm working with battery power and even
> though we're talking 12 volts, I'd like an extremely low reference. About 3
> volts. So I'm toying with the idea of using an externally pumped reference.
> But I don't want it to drift too much with temperature. The idea is that it
> won't drop out till the battery, a small 12 volt SLA, gets below 3 volts.

   How exactly do you plan to get 3V out when your battery is down to 
that level?  Now utilizing an LM4040 buffered through an op-amp will 
allow you to get down to less than 4V before the reference starts losing 
it and that's pretty good if you ask me.
   Granted, you have a couple of problems.  In order to have any 
reference regulate with a small voltage overhead (i.e. 3V ref, 4V 
supply), you have to use a small current reference resistor (usually 1K 
will suffice).  At 'higher' voltages, this will cause the reference to 
eat up more power and your battery won't last as long.  But if you use a 
larger reference resistor, you can get more battery life, but it will 
start losing regulation sooner (say 5 or 6 volts instead of 4).  You'll 
have to choose the best optimal performance.
   I forget if there is a LM4040-3.0V, but I use 4.1's at work and you 
can get the voltage down to 3 by dividing the output with a 20K and a 
60.4K resistor.

> Also, This little package will get quite hot under certain circumstances so
> I want to put a temperature controlled fan on it. I've got an old CPU fan I
> can adapt. I was wondering if anyone has any good ideas about sensing the
> heatsink temperature with a transistor so that it can control the fan. It
> doesn't necessarily have to even switch the fan in and out. If it's easier,
> it could just redirect current to the fan as the heatsink gets hotter. The
> hotter it gets the faster the fan turns. The idea is that if there's no need
> for cooling it can save a bit of battery by not running the fan.

   This seems to be a really complicated for a simple battery powered 
circuit.

> It would take me too long to explain what this is all about but trust me,
> it's electronic music related. Juergen's 5 volt EGs and LFOs are concepts
> not lost on me at this point. But as usual I wannna get this thing out of
> the way as quickly as possible so I'm hoping that someone could point me at
> something that will do the job.

   Good luck and let us know if it works.

   Tony

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I can't drive (my Moog) 55!        |     The E-Music DIY Archive
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Tony Clark -- clark at andrews.edu    | aupe.phys.andrews.edu/diy_archive
http://aupe.phys.andrews.edu/~clark|     Contributions welcomed!
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