ca3080ota.lfo

[Christopher_List at Sonymusic.Com]

The Electronotes Tri-Square VCO is based on this design and is an excellent
1v/oct VCO - I should know, I've built 5 of them. Three for audio, and two
with less features and larger caps that I use as vc-lfos. Using a MAT-03
transisitor pair and a tempco resistor in the exponential converter results
in great tracking range and temp. stability (although I think the VCO in
the ASM-1is a little bit better).

You should connact Bernie Hutchins for the Electonotes Preferred Circuit
Collection - I think it will answer a lot of your questions, give you a lot
of these circuits, and it even describes a lot of the tradeoff in
standards. It's also not too expensive - well worth the investment. Both of
the above mentioned VCOs are in the PCC. It's almost like required reading
for this list!

Here's the address;

Electronotes
1 Pheasant Lane
Ithaca, NY 14850-6399

Anybody got the phone number?

- CList


To:
cc:        (bcc: Christopher List)
From:     martin.czech @ itt-sc.de @ WORLDCOM
Date:     02/07/97 04:50:29 PM CET
Subject:  ca3080ota.lfo




Has anybody made experiences with the ca3080 OTA/CA3140 buffer
Function Generator Circuit ?
(as proposed in data-sheet/app. note ca3080.pdf page 4,
(or in data-sheet/app. note ca3140.pdf page 9)

on the Harris web pages:

"http://www.semi.harris.com/datasheets/lin-tel/ca3080/"
"http://www.semi.harris.com/datasheets/lin-tel/ca3140/"

The Harris people claim a 1E6:1 sweep range  (they call it "super
sweep generator") and there is reason to believe this,
since an oszilloscope foto (1Hz - 1E6 Hz) is supplied in the data sheet.
Ok, they don't tell us about the linearity over such a wide range.
I guess , it'll be awfull and not useable for precision vcos,
but it might serve as a wide range vclfo if I tune it down with a larger
cap. A linear application could be vco in a pll circuit (tri,sin,squa).

Or one could combine this with an  cheap pnp-exponential generator (CA3096
array)
like in the old Formant ota-filters
to approximate an exponential scaling (the CA3096 has two pnps but
they are NOT matched (layout foto)).

I am currently thinking about how to combine this circuit idea
with the symmetry modulation idea in my last mail.
A symmetry modulation independent from frequency requires a very large
sweep range, so this could work (more or less).
The MAX038 can only sweep over a range of 500:1, and the frequency will
certainly suffer at both ends if the symmetry is at it's maximum of
90%/10%. The MAX038 is also quite expensive here in Germany (38,00 DM).


m.c.