[sdiy] ASM1 VCO input question

[Happy Harry]

Hi Roman

(looks at ASM1 schematic) Yes, that is a summer. It will not
matter if you ground or float the inputs, because in either
case, no current will flow...

An example of the 'other' method is the EFM VCO3 (i think its
a Rogue clone). This works OK in a prepatched synth where the
sources are always connected.  I was doing routing of an LFO
where a toggle selects the destination VCO/VCF. When you switched
it to 'off' the VCO would change pitch... because a teeny tiny
current no longer had a path to flow...

The inverting summer would have cured this... OTOH I was already
in the box (1U) and out of room so I used a straight voltage follower
so that the input to the VCO was zero volts (and low impedance) when
off.

Nice to hear (think) that I might have been able to use a different
switch (to ground) or even a low value resistor to eliminate / minimize this 
effect.

H^) harry

of course some folks might noy agree with the semantics of a difference 
between 'summer' and 'mixer'...


>From: Sowa Roman <Roman.Sowa at upc.com.pl>
>To: "'harrybissell at prodigy.net'" <harrybissell at prodigy.net>,   
>buchi at takeonetech.de, synth-diy at dropmix.xs4all.nl
>Subject: RE: [sdiy] ASM1 VCO input question
>Date: Fri, 17 May 2002 17:56:08 +0200
>
>Hi, my comment below
>
>__-----Original Message-----
>__From: Happy Harry [mailto:paia2720 at hotmail.com]
>
>__
>__The resistors described in the start of the thread constitute a
>__'mixer' but are not a summer.
>__
>__Those CV inputs that go direct into the expo tranny are really
>__a mixer... to remain in scale you MUST terminate them in a low
>__impedance (ground unused, etc).
>
>b... b... but in ASM1 VCO schemo I've got, CV inputs use
>inverting opamp, don't go directly to expo tranny. :)
>So it is a summer then, huh?
>
>Roman
>
>
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