Tempcos

[Roland U K Ltd]

FROM:	 101574,2042 at compuserve.com
TO:	synth-diy
DATE:	5/7/96 9:29 AM

Re:	Tempcos

Hi list,

Has anybody actually tried using tempco's in the Electronotes VCO circuits?   I
put a couple of 1k's ( all I could get over here ) in place of the 2k metal film
in the EN76 tri-square and it made things worse.  The osc definitely became less
stable and started to drift .  Now, the tempco was the correct type with 3300ppm
rating so what could be going on?   It's a feedback system that seemed to add
instability, and taking them out resulted in the osc. going back to its normal
behaviour.   I'm using an Elantec quad PNP dil package  ( only L2.60 ) so I
wonder if it is just not so sensitive to temperature changes.   You can
certainly touch it for quite a while without hearing any drift whereas , with a
discrete transistor, touching it instantly affects it.  ( As I learnt while
matching up transistors for the Moog type VCF ).
So maybe the tempco is reacting much quicker to slight fluctuations in
temperature whereas the Elantec PNP's do not due to their construction.  This
would cause errors would it not?
Any ideas?  It's not really a problem as the OSc is very stable as it is ( ie no
tempco ).  But it worries me that the tempco made things worse.

Thanks

Joe Farler