Andrew, you meant a second 220K resistor, not 220 ohm. I'm about to
build my dual Synthacon VCF (two in 2U), and I'll be trying these CV
resistors values, based on a suggestion by Mr. Loffink: 680R from base
of 2N2222 to ground; 430K for the initial freq pot; 360K for the
"1V/Oct" input'; 150K for the FM input with attenuator pot.
I see from your proposed Stooge panel that you would put mixer pots on
each of the inputs. If you make three simple mixers for the inputs, you
can easily add an attenuator pot for the Allpass input. The mixer
circuit is easy to visualize. The phase is inverted, but it probably
doesn't matter. (Now will this drawing come through?)
LP input section:
------[100K]---------
| |
| - TL072 |
From LP attenuator ------------[100K]------o--------|
\ |
| | \ |
From Allpass attenuator ---------[100K]------| |
>--------o--------> LP IN (47K on board)
+ | /
------| /
|
///
Repeat for BP and HP inputs. The allpass input connects to each mixer.
-Richard Brewster
John Loffink wrote:
>1. Yes, just scale the input resistor, but don't expect steady tracking.
>This filter is all over the place in pitch when it self oscillates.
>
>2. Yes.
>
>3. No, you need three mixers IIRC. One each for LP, BP, HP, Allpass goes
>to all mixers. LP, BP and HP inputs go to each individual mixer.
>
>John Loffink
>The Microtonal Synthesis Web Site
>http://www.microtonal-synthesis.com
>The Wavemakers Synthesizer Web Site
>http://www.wavemakers-synth.com
>
>
>
>
>>-----Original Message-----
>>From: synthasaurus [mailto:ixqy@...]
>>
>>
>> Hi all,
>> I was thinking of have a 2U Stooge panel made for the CGS Synthacon
>>filter. I uploaded a tentative layout (a .jpg) in the files section of
>>this list's Yahoogroups (now LaunchGroups?) webpage:
>>
>>http://launch.groups.yahoo.com/group/ModularSynthPanels/files
>>
>>or the short, direct link:
>>http://tinyurl.com/28tlm
>>
>>
>> I was talking to Larry Hendry about some adding some features that I
>>saw on other Synthcon VCF panel designs. Can anyone help with the
>>following questions, please?
>>
>>1. Can a 1v/oct input be implemented without too much trouble?
>>
>>2. Could a second FM Input be added by using a second 220 ohm resistor
>>tied to the base of the 2n2222?
>>
>>3. Could an All Pass input jack be added by using three extra 47K
>>resistors tied to the LP/BP/HP inputs and a pot?
>>
>>
>> Thanks in advance for any help. I'm hoping these features will be
>>easy to add on, so that others might want to order a Stooge panel.
>>
>> The ever-so technically challenged,
>> Andrew Sanchez
>>
>>
>>
>>
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