Cgs synth

on 1/25/02 5:34 PM, sasami@... at sasami@... wrote:


8brain@... wrote:

>Tonight I finished my first psycho LFO. I made a few
>modifications:

I've done some extensive playing around with the Psycho LFO too.

>1)put a 1 meg pot on every oscillator, copying the circuit for the
>lowest one on the schematic. This provides a great deal of
>variety.

1 Meg pots, along with 4k7 fixed series resistors give a range that goes up
into low audio rates.

>2)I found the 1meg pot/2.2uF to provide too much slew, so I
>changed the cap to .22 uF.

2.2uf really needs 100k pots. I explain that in the text. The 1 meg lets you
really flatten it out to almost nothing - not the sort of effect every one
is after, though of use in some instances. In the last one I built, like
you, I went to .22uf when I accidently purchased 1M pots.

>3)Added an LED, plus an LED driver that's probably overkill.
>(That's what I get for hanging out on the MOTM mailing list.)
>Schemo is here:

I tried a similar arrangement on one, and it did work, nicely cancelling out
the LED voltage drop, though I needed to run several at once, and the chip
from which I was driving them was getting too hot. It may be fine with one
LED per chip, but using a quad op-amp and driving two LEDs is not
recommended. I abandoned them in favor of a transistor wired as an emitter
follower, running from a special power rail set at -2.2V to bias the LED to
start glowing at just above 0 Volts. The advantage of the circuit you've
listed though is if you use a bi-color LED (of the back to back two - leaded
package type) you should have a LED that lights green for positive levels
and red for negative levels. That would be of no use in the Psucho though,
because its output remains above 0 all the time.

>I'm very happy with the module. It's a very interesting modulation
>source. Driving a VCO with the portamento turned up a bit and
>the oscillators going at different frequencies I get really cool
>pseudo arabic folk melodies. Hours of fun!

Good to hear! We need more people to share their ideas and experiences here.

Ken
_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>


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[Non-text portions of this message have been removed]

>I tried your suggestion using 5.1K resistors. Nice! Adds just the right
>amount of extra range.
>
>One request I have for this PCB - if you re-release it, please add an LED
>driver on the main PCB. A driver for each oscillator would be even nicer.
>Emitter follower circuits don't take up much space, so 5 little drivers
>would be cool~! Just a fan of visual feedback, I guess.
>
>Love this little module. Finished the second one today.
>
>R.

_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>