[sdiy] ASM-1 VCO / keyboard

[patchell]

Jimmy Gogas wrote:

> Hello guys,
>
> I was wondering if anyone can explain me what the asm-1 vco inputs are
> exactly? Looking at vco schematic, I noticed that there are 6 CV, 2 linear
> FM, 2 pulse width and 1 sync input. I know what the CV inputs are (why do we
> need 6?), but I'm not quite sure what the rest are.
>

    Linear FM: These are frequency control input, but they control the frequency
linearly.  These are used to frequency modulate the signal....although, I am at
a loss for words to explain exactly why this is desireable (I know why, the old
brain just can't seem to come up with a way to explain it...)

    The pulse width inputs control the width of the pulse output  As you change
the pulse width, the relative amplitude of the harmonics change.  For example,
50% width has only odd harmonics.  25% will have odd and even harmonics,
although some of them will be missing (don't remember which ones off the top of
my head).

    The sync input is used to synchronize the oscilator to another signal.
When the sync input makes a transistion (can't remember if it is rising or
falling edge), it will reset the oscilator saw tooth back to a particular state.

    And you need 6 frequency CV inputs because one will probably be course tune,
one will be fine tune, one will be your primary pitch input, and perhaps another
will be from an LFO to give a bit of vibrator, and maybe other input will come
from an envelope generator to give a momentary oscilator sweep...you can never
have too many inputs on you VCO frequency control.

>
> I still haven't built my cv keyboard with interface yet, so I still don't
> know what the outputs of that are going to be. Is there actually a simple
> interface I can built that will output all these vco inputs? If yes, can I
> have the schematic? If not, should I buy myself a MIDI keyboard and a
> MIDI/CV converter? Will that be enough? Any suggestions on what MIDI
> keyboard and MIDI/CV converter I should get?

    Generally, the only output from a Midi->CV converter that your VCO will be
interested in will be the pitch output.  The other other that is pretty
important is the GATE output, which indicates when a key is pressed.  This will
generally go to an envelope generator.  Other posible outputs from a Midi->CV
converter might be VELOCITY, which indicates how fast the key was pressed.  This
might be used for controlling a filter parameter.  PRESURE is another output you
could posibly have, which would indicate how hard you are pressing on the
keyboard.  PITCH-BEND is another posible output, this would of course probably
go to the VCO, but you could also run it to the filter as well....many many
posibilities.

>
> Thanks in advance.
>
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--
 -Jim
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