[sdiy] PAIA VCO, LM13700 diode temp comp.

[phillip m gallo]

Karl,

After decades of staring at the National "app note" and wondering what it's
result would be, PAIA's publishing of their VCO implementation based upon
the technique finally caused me to break down and try the approach.

I built a pair of VCO's based upon the PAIA scheme for the sawtooth core
(but used different wave shapers).  As Jim points out the Gm of the OTA is
what temp. compensates the core.  My variance from the PAIA implementation
was;

1)using a REF-02 for expo, comparator and waveshaper references.
2)used MAT-03's for the expo pair,
3)used an AD823 for the integrator buffer on one VCO and a LF412 for the
alternate.
4)implemented a POT for the Hi-Fz tracking adjustment.
5)"leveled" the MAT03's to the height of the socketed '13700 so they could
share a piece of aluminum as a common radiator.
6)As is my general practice i used 1% and 2% film resistors (for what that's
worth).

I implemented the VCO's on perf board so i could wire separate ground star
networks for the AC and DC circuit components (meeting at supply input).
Given the parts, you can build the core in an evening to analyze your
impression of the circuit.

I was quite pleased and testing exhibited better results than that reported
by Ian but one set of test i didn't do was swap a variety of '13700's into
place to note their effect.  Both VCO's did perform similarly.  The VCO's
and notes from testing are still in storage although i moved nearly a year
ago (those who've visited my garage understand).  I'll be digging the VCO's
out of storage for project reasons in a few weeks and re-run the tests if
you're interested.

regards,
p

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of karl dalen
Sent: Monday, October 17, 2005 4:42 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] PAIA VCO, LM13700 diode temp comp.


Long time ago there was discussions on the PAIA
VCO temp drift compensation using the diodes of
the LM13700, how did that turned out?

Was it a good idea of temp compensation?

REG
KD


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