ok, for the last few days I've been thinking of how to add VC-Res. I've
got a few ideas, but I'd like to hear other people's opinions.
1. easiest (I dont' like it much). use a Vactrol in place of the res
pot. This would be slow.
2. replace the 2n2222/2n2907 amplifier section of the filter with an OTA
based VCA. From my calculations, It seems the amplifier has a gain of
about 1.2 with the res pot at minimum, and a gain of about 2.3 with the
res pot at maximum (I made many approximations when I did it). The Nyle
Steiner paper that describes this VCF states that the an opamp can
replace the amplifier and the gain of that amplifier determines the Q of
the filter. Since some people have shown interest in a VC-Res mod, I
thought I'd ask what you think about replacing the 2n2222 and 2n2907
with an opamp.
3. I'm still thinking of more possible ways. one might be to build a new
voltage/current controlled amp out of discrete transistors. or a
discrete transresistance amp with a OTA in front of it. thats basically
like idea 2 without an opamp. I haven't came up with a good circuit for
this yet. dont' know how easy it will be to do.
I'm a bit hesitant about using an opamp because it seems that the
transistors have an effect on this filter's character. I'm afraid of
messing that up.
,ryan
got a few ideas, but I'd like to hear other people's opinions.
1. easiest (I dont' like it much). use a Vactrol in place of the res
pot. This would be slow.
2. replace the 2n2222/2n2907 amplifier section of the filter with an OTA
based VCA. From my calculations, It seems the amplifier has a gain of
about 1.2 with the res pot at minimum, and a gain of about 2.3 with the
res pot at maximum (I made many approximations when I did it). The Nyle
Steiner paper that describes this VCF states that the an opamp can
replace the amplifier and the gain of that amplifier determines the Q of
the filter. Since some people have shown interest in a VC-Res mod, I
thought I'd ask what you think about replacing the 2n2222 and 2n2907
with an opamp.
3. I'm still thinking of more possible ways. one might be to build a new
voltage/current controlled amp out of discrete transistors. or a
discrete transresistance amp with a OTA in front of it. thats basically
like idea 2 without an opamp. I haven't came up with a good circuit for
this yet. dont' know how easy it will be to do.
I'm a bit hesitant about using an opamp because it seems that the
transistors have an effect on this filter's character. I'm afraid of
messing that up.
,ryan