|
3D MODEL
This Compact VCO started out life as
a replacement for the original VCOs in Ken's
'73 Serge, so it replicates a lot of the
functionality of that module. Of course there
have been numerous enhancements to the design
as well, making it right at home in a
1V/Octave synthesizer. The core chosen is the
well known Electronotes ENS-76 VCO Option 1 as
used in the ASM-1, Modulus, etc.
This core was an obvious choice due to the
amount of information, lists of suitable
substitutes and so on that are available on
the web.
It has AC and DC linear CV inputs as
well as 1V/Octave inputs and
scalable/reversible CV inputs. It has sawtooth
and pulse/square outputs, as well as a
waveshape that is variable between sawtooth
and a "sine-like" shape, and a fixed
"sine-like" output too. It also includes a
simple sub-oscillator for those who wish to
experiment with that.
The [FINE] control is wired as a dual
function control:-
- Between its mid-position (12
o'clock) to fully clockwise position (5
o'clock) the frequency range of the VCO is
from around 8Hz to over 14kHz
- Between its mid-position and fully
anti-clockwise (7 o'clock) the VCO can be
driven down to LFO speeds as low as 1 cyle
per 4 seconds
The sub-oscillator is based on that
from an LM3900 application note (AN-72), but
will not cover the full range available from
the VCO core itself.
This Compact version omits a handful
of features/functions dictated by the
requirement of the smaller panel space:-
- There is only one 'voltage
processor' input - [VC F]
- There is only one 'frequency
modulation' input [1V/OCTAVE] (J103 is
assigned to the [FREQUENCY] control)
- There is no DC copy of the
[VARIABLE] waveshape
- There is no [PLS] output from the
staircase generator
- There is no [STEPS] control for the
staircase generator. This is fixed to a
defined number of steps as part of the
calibration process. As such, the
[STAIRCASE] output is a fixed sub-octave of
the main frequency
- There is no external input to the
staircase generator, this is hardwired to
the [PULSE] output
- There is no [SYNC] input to the
staircase generator .
Note that the "sine-like" waveform
is not a pure sine wave. There is a
significant glitch in it that is almost
impossible to trim out. As this is the
recreation of a module that had such a
waveshape, this is appropriate. If you
require an accurate sine wave, this module
is unsuitable for that purpose.
|
