Joined: Nov 20, 2006
Location: The Automotive Capital of Canada
|Posted: Tue Jul 10, 2012 1:27 pm Post subject:
VCO-1 on +/- 12V?
Just wondering if anyone is successfully using Thomas' VCO-1 on a 12V supply?
I know R23 and R43 change, is there any other changes that anyone would suggest making?
Joined: Aug 16, 2011
|Posted: Thu Jul 12, 2012 1:22 am Post subject:
|Time ago I wrote this:
The basic idea is to look for current and voltage references, offsets and amplitudes.
The number references of the components refer to the schematics of the VCO1 that you can find here: http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html
R43 provides a current reference. You change it with a simple rule of three, so if for 15V is 1.5M for 12V is 1.2M
The coarse and fine controls will see reduced their span.
Look that with a +15V/-15V supply, the coarse control does span 30 octaves. So maybe in this case you don't need to change it. With a +12/-12V supply it does span 24 octaves.
However, if you desire decrease or increase the span, it is achieved increasing or decreasing R28.
About the fine control, it could be useful to change it. For example for a +15/-15V supply R46=3M, it does span one octave. So, for a +12/-12V R46=2.4, it does span also one octave.
This could be useful useful for all expo converters... like the one in the VCF1
At this point I bread-boarded the VCO1 core and its waveshapers.
I measured the triangle output and the amplitude was about 8 p-p , I achieved it to be close to 10Vp-p with:
Then, for the sine output I achieved 10V p-p with:
For the pulse output I expected also a smaller output, since the comparator goes from one rail to the other.
I achieved 10V p-p and 1KΩ of standard output impedance with:
Finally, we have R41. It decides the pulse width span of the potentiometer.
In my breadboard, I noticed that with R41=265K, the pulse goes from approx. 5% to 95% . Other folks could prefer other configuration.