[sdiy] my VCO OSCILLATING!

[Michael Ruberto]

Whoa!!! I just hooked the output to speakers. This is one FAT PIG BEAST of a 
VCO!!! It makes my old ASM1 type VCOs sound anemic. Holy ground shakers 
Batman!
Comparing with some samples of an actual SEM it has the same dry character 
but mine seems a bit brighter and has a bit more "edge" to it. Most likely 
the recording had the life MP3ed out of it.

On the scope the waveform has an exponential curve to it's slope prior to U3 
and a rounded log type slope from U3s output. Tri and Sine waves are all 
messed up but I haven't touched the trimmers for the shaping circuits yet. 
Although, the messed up waves do sound kinda cool.

I connected a perfect 1 volt ramp from my Tektronix Test Display Generator 
to the CV input and I'm not quite getting an octave. When I get done 
drooling over what's coming from the speakers I'll attempt to adjust the 
tracking again. Droooooooollllll....

M. A. Ruberto


>From: "Michael Ruberto" <frankentron at hotmail.com>
>To: synth-diy at dropmix.xs4all.nl
>Subject: [sdiy] my VCO OSCILLATING!
>Date: Sat, 10 Dec 2005 00:41:16 -0500
>
>Sometimes if you stare and make threatening faces long enough analog 
>circuits start to work. But not this time. Like Tim pointed out there was 
>an error in the original schemo that I didn't catch. However, following 
>that correction came a freaky streak of failed parts. On my work bench I 
>have a small graveyard of transistors. They were all brand new parts too.
>
>Anyway, The VCO is now making a nice glitch-free saw but the frequency 
>range is very low. The pitch knob is only giving me around 1 - 50 Hz. I 
>toyed with the trimmers for awhile but could only manage to reduce the 
>range even more. I'm too tired to figure out this issue tonight. I suspect 
>the 2SC1583. Some resistor values will probably have to change. That will 
>be tomorrows chore after I work on the car.
>
>M. A. Ruberto
>
>