[sdiy] uA726 temp setting

[Barry Klein]

Is there means to measure current through pin 8?
I would think that you could then set your trimmers all to say 75K and
monitor current through pin 8 for max and min frequency (the operational
range).  You then would have to look at the temp C' vs supply current graph
in the ua726 spec to set the trimmer to get this operational range totally
above the worst case temp. inside the synth case.  Change all trimmers to
this new value, and then maybe set freq. to midrange and match all currents
of all circuits.  Sound like a plan?

Barry



-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Grant Richter
Sent: Friday, March 18, 2005 8:47 AM
To: Kevin Lightner; synthdiy
Subject: Re: [sdiy] uA726 temp setting

Hi Kevin,

May I suggest looking at the setup procedure for the Moog Source
oscillators?

Those are based on a thermostated CA4046. The procedure is given for setting
the internal temperature to 130 degF, by measuring the millivolt drop at the
expo transistor base-emitter junction. The BE drop increases by 2.2
millivolts per degree, so you can measure the internal temperature by
measuring the BE voltage. The formula is given in the Source service manual.

Reliability of solid state devices is directly related to temperature. Using
a lower temperature will extend the uA726 lifetime.

> 
> So, does anyone have any idea what this should be set to?
> I don't care how it's expressed: resistance, voltage or current.
> One would guess the setting to be somewhere 150K or over, or they
> would have installed a 100K trimmer (or expect 726 tolerances to be
> very different from each other.)
> 
> Any clues would be nice.
> Getting a Sonic Six to track well is hard enough when the temp IS set
> correctly, but it's almost impossible if it's off.
>