[sdiy] CEM 3340 as lfo, CA3080 as tri->sin (barry klein) hey that rhyms...

[Scott Bernardi]

To lower the frequency range, try increasing the integrating cap. I think they
typically use 1000pF, try 0.1uF. Use a good quality 0.1uF though, not a ceramic
disc.
I've done three types of sine converters:
3080 based, see http://members.home.net/sbernardi/elec/og2/og2_lfo.html
FEET based, see http://members.home.net/sbernardi/elec/og2/og2_ssm2033_vco.html

2 1N4148 based, see http://members.home.net/sbernardi/elec/og2/og2_cem3374.html

The 1N4148 based is the easiest. The 3080 based seems to give the best output.
The key to a well shaped sine is that you need two trimmers - one to adjust the
amplitude of the triangle you are going to warp, and the other to adjust its dc
offset.

TooManySynths wrote:

> Hi All,
>
> What's the correct way to scale a 3340 down to LFO
> range?  I tried just summing -15 through a 10k
> resistor with the other CV inputs, but it still only
> goes down to about 2hz.
>
> I added the tri->sin converter from barry klien's
> book. If you have the book it's on page 105.  At any
> rate the 3080 just pumps out a huge square wave.  This
> circuit has been sitting for a couple of weeks and I
> thought perhaps I'd look at it again and be able to
> see what I was missing.  I can't!  If I increase the
> resistance to pin 5, which I thought this would lower
> the current, hence lower the gain, it still looks like
> a square wave.  If I just touch pin 5 and the input
> resistor lightly, it seems to settle down a bit, but a
> five meg resistor didn't change it at all.  So, I
> thought maybe the input level is too high, and lowered
> that by feeding it through a voltage divider to
> ground.  It eventually just stops working.  Any ideas?
>
> Thanks
> Daryl
>
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--
Scott Bernardi
sbernardi at home.net