<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<div class="moz-cite-prefix">Ah, the original dude himself appears
:-)<br>
Thanks for describing the procedure! I'm sure I would have fried
at least one IC otherwise - well I might still, but maybe fewer
:-D<br>
<br>
Thanks also to the others who replied with some interesting
comments.<br>
<br>
<br>
Steve<br>
<br>
Am 29.02.2016 um 15:05 schrieb Rick Jansen:<br>
</div>
<blockquote cite="mid:56D45011.8070501@xs4all.nl" type="cite">
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<div class="moz-cite-prefix"><font face="Helvetica, Arial,
sans-serif">Well, talking about a blast from the past :-)<br>
<br>
It's hardly my circuit though, it's from the AN-299
application note.<br>
<br>
Heating up the 3046 does not cost much power, it's mass is
just a few grams, and the chip is not hot to the touch.<br>
<br>
This is what I wrote in my documentation:<br>
<br>
1. Heater adjustment<br>
<br>
First make sure the heater is switched off by shorting D2.
This way the base of the heater is grounded and Q5 switched
off. Now measure the voltage present at the +-input of A1.
This must be done with a digital voltmeter (DVM) or another
voltmeter with high input impedance. A regular multimeter will
not do. The voltage measured must be about 650 to 700mV, being
the Ube of the sensor Q3. <br>
<br>
Do not apply power unless the heater is adjusted or switched
off!<br>
<br>
With every degree temperature rise this be drops 1.9mV. In
operation A1 will make Q5 heat up the 3046 array until the
voltage at the plus-input is the same as the (set) voltage at
the minus input of A1. So, you now need to adjust P1 so that
the minus-input of A1 is fed with the voltage that goes with
the elevated temperature. should with the elevated
temperature. To compute this set voltage subtract the
temperature rise (in Celcius) times 1.9mV from the measured
voltage. <br>
Example: you want a 30 degrees temperature rise and the
measured Ube is 695mV. The desired drop in Ube therefore is
30x1.9=57mV. The minus-input of A1 must be set (with P1) to
695-57=638mV. </font><br>
<br>
rick<br>
<br>
On 29/02/2016 01:33, <a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:sleepy_dog@gmx.de">sleepy_dog@gmx.de</a> wrote:<br>
</div>
<blockquote cite="mid:56D391EF.4010301@gmx.de" type="cite">
<pre wrap="">Hey there,
first a question about thermistors (this is what "tempco" are, correct?)
In circuits for voltage control of a VCO or VCF which use a tempco, how
much could one deviate with the coefficient, say for instance in Thomay
Henry's newest VCO based on the TLC555 timer? I think it was spec'd at
3500 - what if I could get one with 3470 or 3600 more easily?
Also, I find Rick Jansen's Moog VCF schematic interesting, which uses 3
remaining transistors in a 3046 transistor array as a controlled "oven"
for the NPN matched pair, to get rid of temperature sensitivity.
How come I don't see this kind of solution more often? Is the tempco
solution "better"?
How much current will the "oven" draw, and does this reduce the lifetime
of the IC?
Regards,
Steve
_______________________________________________
Synth-diy mailing list
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:Synth-diy@dropmix.xs4all.nl">Synth-diy@dropmix.xs4all.nl</a>
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://dropmix.xs4all.nl/mailman/listinfo/synth-diy">http://dropmix.xs4all.nl/mailman/listinfo/synth-diy</a>
</pre>
</blockquote>
<br>
</blockquote>
<br>
</body>
</html>