ASM-1 and Tempcos

Joe Farler joef at roland.co.uk
Tue Jan 28 22:56:18 CET 1997


I've been building up the ASM-1 VCO so I thought I'd share one problem
with you in case anybody else comes across this.
The oscillator works fine but I had a problem when I put the 1K
tempco in.  It made things worse.
I didn't understand this at first but when I measured it it was
slightly over 1K at room temp.  So I put my finger on it to warm 
it up and the resistance went down.

So be warned: the Tempco's from Farnell have a negative coefficient

If you put them in they will double the error rather than correct 
it.

These were 3,000 ppm 1K resistors, part number 143-584.

A call to Farnell Tech Support confirmed this.

The catalogue lists them as 3000 ppm ( no minus sign ) but the small 
print gives a ratio of resistance at 25'C to 125'C as 1.37 i.e. a
negative coefficient.  Oops :(


On a slightly different note, anybody building the ASm-1 type osc as a 
separate module please note that pins 1 and 4 on the 311 are 
connected together.  I don't think this is shown on Gene's original
schematic.


Joe.



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