Modular Synth Panels

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

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
>
>

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
>>
>>
>>
>>
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>
>
>
>
>

LOL! Nope. It looked nice before I sent it :).

Richard Brewster wrote:

>(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
>
>
>
>

Hi,
Thanks to Richard and John (and Larry!) for the helpful replies. I wasn't
too sure what circuit was being mention for the All Pass input, but after
re-reading -

Do you mean each of the three existing inputs on the PCB (LP/BP/HP) would
need an opamp mixer in order to sum the All Pass to each of the three said
inputs? Is this because a passive mixer would load the inputs? Sorry for the
technician part of me showing. ;-)

I'm curious...Is there anyone reading this that would be interested in
ordering this Stooge CGS Synthacon panel? If not, I might just have to go homebrew.

Thanks everyone,
Andrew Sanchez


In a message dated 3/10/04 8:21:04 PM Central Standard Time, pugix@...
writes:

> 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?)

In a message dated 3/10/04 8:21:04 PM Central Standard Time, pugix@...
writes:

> Andrew, you meant a second 220K resistor, not 220 ohm.

Oops! Sorry, I was half asleep and going from memory (a scary thought!) when
I wrote that last night. Kind of like...NOW! lol!!!

Thanks again, :-)
Andrew

ixqy@... wrote:

> Do you mean each of the three existing inputs on the PCB (LP/BP/HP) would
>need an opamp mixer in order to sum the All Pass to each of the three said
>inputs?
>

Yes.

> Is this because a passive mixer would load the inputs? Sorry for the
>technician part of me showing. ;-)
>
>

Basically, yes. The Synthacon VCF inputs presume a single low-impedance
signal coming in. Injecting two signals at any of these inputs really
calls for a proper mixing circuit.

What's the opinion about the All pass feature? I know Cynthia Webster's
version of the Synthacon has it, but there is not a separate attenuator
for the All input.

-Richard Brewster

Reading all of this, I don't know why the wheel is try to be reinvented:

http://www.cyndustries.com/modules_synthaconfilter.cfm

> What's the opinion about the All pass feature? I know Cynthia Webster's
> version of the Synthacon has it, but there is not a separate attenuator
> for the All input.

The reason there is no "ALL INPUT" attenuator, is because it would not be
useful for anything AFAIK. You generally use "ALL INPUT" when you are not
using the other 3 filters TTBOMK.

The easiest thing to do would be to ask Cynthia directly about this. Also, she
is willing to sell stuffed boards separately. An excellent value IMO.

If that doesn't suite your fancy, try using a few of Peter G.'s Gizmo boards
with Ken's PCB. The Gizmos will take care of this for you with out all of the
fuss and bother.

Cheers!
Todd

__________________________________
Do you Yahoo!?
Yahoo! Search - Find what you�re looking for faster
http://search.yahoo.com

Got a link for information on the Gizmo board?

Tentochi wrote:

>If that doesn't suite your fancy, try using a few of Peter G.'s Gizmo boards
>with Ken's PCB. The Gizmos will take care of this for you with out all of the
>fuss and bother.
>
>
>

If you are doing it for the experience, then go for it. But I don't have
enough time in my day as it is. Ha!

I haven't tried them yet, so let us know if you use them. They look like they
will take care of business. And Peter was very helpful with me on another
project.

http://www.buzzclick-music.com/gizmotron.html

Cheers!
Todd

> Got a link for information on the Gizmo board?
> >If that doesn't suite your fancy, try using a few of Peter G.'s Gizmo boards
> >with Ken's PCB. The Gizmos will take care of this for you with out all of
> the
> >fuss and bother.

__________________________________
Do you Yahoo!?
Yahoo! Search - Find what you�re looking for faster
http://search.yahoo.com

I highly recommend you dedicate an Oakley Multimix with the Hendry triple
attenuator modifications to the Steiner VCF without attenuators. This gives
you three reversing attenuators for three different inputs to the Steiner
VCF, or use just one input through the Multimix to all three Steiner VCF
inputs to get the all pass mode.

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: Richard Brewster [mailto:pugix@...]
> Sent: Thursday, March 11, 2004 6:37 PM
> To: ModularSynthPanels@yahoogroups.com
> Subject: Re: [ModularSynthPanels] CGS Synthacon VCF Stooge panel
>
>
> ixqy@... wrote:
>
> > Do you mean each of the three existing inputs on the PCB (LP/BP/HP)
> would
> >need an opamp mixer in order to sum the All Pass to each of the three
> said
> >inputs?
> >
> Yes.
>
> > Is this because a passive mixer would load the inputs? Sorry for the
> >technician part of me showing. ;-)
> >
> >
> Basically, yes. The Synthacon VCF inputs presume a single low-impedance
> signal coming in. Injecting two signals at any of these inputs really
> calls for a proper mixing circuit.
>
> What's the opinion about the All pass feature? I know Cynthia Webster's
> version of the Synthacon has it, but there is not a separate attenuator
> for the All input.
>
> -Richard Brewster
>
>

In a message dated 3/11/04 8:35:54 PM Central Standard Time,
jloffink@... writes:

> I highly recommend you dedicate an Oakley Multimix with the Hendry triple
> attenuator modifications to the Steiner VCF without attenuators.

Yep, this sounds like the way to go. Thanks everyone for the input and
recomendations. If a Stooge panel were to be made, it might be best to delete the
All Pass and 1v/oct inputs from the panel graphic I uploaded.

Andrew

>
>Reading all of this, I don't know why the wheel is try to be reinvented:
>
>http://www.cyndustries.com/modules_synthaconfilter.cfm
>
>> What's the opinion about the All pass feature? I know Cynthia Webster's
>> version of the Synthacon has it, but there is not a separate attenuator
>> for the All input.
>
>The reason there is no "ALL INPUT" attenuator, is because it would not be
>useful for anything AFAIK. You generally use "ALL INPUT" when you are not
>using the other 3 filters TTBOMK.

There is no All attenuator because the attenuators are all POST MIXER. i.e,
you feed a signal into the all input, and adjust the three pots to give
different responses etc.

Ken (who was responsible for the All functionality in the first place).


_______________________________________________________________________
Ken Stone sasami@... or ken@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>