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CGS VCO

CGS VCO

2004-03-15 by Bob

So,
has anyone got one of these VCO's up and running yet? I am really
curious to hear the what people think about the waveshaper, sub osc
features, and overall sound. I am working on making one up for my
system, but I can't decide if I want to add the kitchen sink or just
keep as a more basic vco... any thoughts would be helpful.
one final thought, there is no pot for Pulse Width on the
schematic, could that be added?

thanks

Howard

http://www.bobknarley.com/synth.html

Re: CGS VCO

2004-03-15 by Richard Brewster

Yes, actually. I got my first VCO board running on the bench
yesterday. I am building two of these, without the waveshaping
circuits. Mine only has the sawtooth and square outputs. It has coarse
and fine frequency pots, an FM input that switches between exponential
and linear, and a 1V/oct input. Also the sync and PWM inputs. I
changed a lot of the VC mixer resistor values, and also used an LT1013
op amp there. This fits in a 1U panel (still to be ordered from Front
Panel Express).

You would need another op amp (similar to the ASM-1 VCO) on the PWM
input if you wanted to add a PWM pot. There is no mixing on that input.

I do have a question for Ken. The sawtooth buffer amp shows a 330K
feedback resistor and a 240K bias on the schematic. I inserted pots and
adjusted to get a +/-5V sawtooth. The values turned out to be exactly
200K / 600K, just like the ASM-1. This is also just what you would
expect to convert the 0-5V signal out of the CA3140. Double the voltage
(200K/100K), then offset the 0 to -10V result back to +/-5. I think
maybe the 330K/240K values are for a +/-12V power supply.

-Richard Brewster

Bob wrote:
Show quoted textHide quoted text
>So,
> has anyone got one of these VCO's up and running yet? I am really
>curious to hear the what people think about the waveshaper, sub osc
>features, and overall sound. I am working on making one up for my
>system, but I can't decide if I want to add the kitchen sink or just
>keep as a more basic vco... any thoughts would be helpful.
> one final thought, there is no pot for Pulse Width on the
>schematic, could that be added?
>
>thanks
>
>Howard
>
>http://www.bobknarley.com/synth.html
>
>
>
>
>

Re: CGS VCO

2004-03-15 by sasami@hotkey.net.au

>I do have a question for Ken. The sawtooth buffer amp shows a 330K
>feedback resistor and a 240K bias on the schematic. I inserted pots and
>adjusted to get a +/-5V sawtooth. The values turned out to be exactly
>200K / 600K, just like the ASM-1. This is also just what you would
>expect to convert the 0-5V signal out of the CA3140. Double the voltage
>(200K/100K), then offset the 0 to -10V result back to +/-5. I think
>maybe the 330K/240K values are for a +/-12V power supply.

Yes, that would be the case :)

Ken
_______________________________________________________________________
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/>

Re: CGS VCO

2004-03-15 by sasami@hotkey.net.au

>I do have a question for Ken. The sawtooth buffer amp shows a 330K
>feedback resistor and a 240K bias on the schematic. I inserted pots and
>adjusted to get a +/-5V sawtooth. The values turned out to be exactly
>200K / 600K, just like the ASM-1. This is also just what you would
>expect to convert the 0-5V signal out of the CA3140. Double the voltage
>(200K/100K), then offset the 0 to -10V result back to +/-5. I think
>maybe the 330K/240K values are for a +/-12V power supply.

More thoughts on this - the ASM-1 sawtooth is centered around 0V, while the
output of mine SITS on 0V, so it is 0V-10V. The +/- 5V wave form is then
available from the AC coupled output. There may be slight offset
differences when running off 15V instead of 12V, but the above is the
primary reason for the somewhat different values.

Ken

_______________________________________________________________________
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/>

Re: CGS VCO

2004-03-16 by Richard Brewster

Ah, that explains it. I wanted a +/-5V sawtooth output. Also, I
DC-coupled the sawtooth to the square-wave comparator, so as to have no
lower limit on frequency of the square wave. This required the
symmetrical sawtooth as well.

-Richard Brewster

sasami@... wrote:
Show quoted textHide quoted text
>>I do have a question for Ken. The sawtooth buffer amp shows a 330K
>>feedback resistor and a 240K bias on the schematic. I inserted pots and
>>adjusted to get a +/-5V sawtooth. The values turned out to be exactly
>>200K / 600K, just like the ASM-1. This is also just what you would
>>expect to convert the 0-5V signal out of the CA3140. Double the voltage
>>(200K/100K), then offset the 0 to -10V result back to +/-5. I think
>>maybe the 330K/240K values are for a +/-12V power supply.
>>
>>
>
>More thoughts on this - the ASM-1 sawtooth is centered around 0V, while the
>output of mine SITS on 0V, so it is 0V-10V. The +/- 5V wave form is then
>available from the AC coupled output. There may be slight offset
>differences when running off 15V instead of 12V, but the above is the
>primary reason for the somewhat different values.
>
>Ken
>
>_______________________________________________________________________
>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/>
>
>
>
>

CGS VCO

2005-03-13 by dustin sedlacek

ok several questions about the VCO , first we are building a vco
are ceramic resistors ok (instead of the metal film ) ? and now what
about the staircase and sub osc ? does the stair case have a input as
listed on the schem ? "staircase in STI" what is this ? i do not know.

Re: CGS VCO

2005-03-14 by sasami@hotkey.net.au

>ok several questions about the VCO , first we are building a vco
>are ceramic resistors ok (instead of the metal film ) ?

Metal film are needed in the core and CV sections for both accuracy, AND
stability. If you are just building a "noise box", ceramic resistors are okay.

>and now what
>about the staircase and sub osc ? does the stair case have a input as
>listed on the schem ? "staircase in STI" what is this ? i do not know.

STI is the input for the staircase generator. You can either connect it to a
panel socket, OR hard wire it to the VCO output.

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

Re: CGS VCO

2005-03-14 by dustin sedlacek

pardon my ignorance , what would be use be of connecting it to a jack
? would it follow a input signal ?

Show quoted textHide quoted text

On Tue, 15 Mar 2005 06:58:25 +1100, sasami@...
<sasami@...> wrote:
>
>
> >ok several questions about the VCO , first we are building a vco
> >are ceramic resistors ok (instead of the metal film ) ?
>
> Metal film are needed in the core and CV sections for both accuracy, AND
> stability. If you are just building a "noise box", ceramic resistors are
> okay.
>
> >and now what
> >about the staircase and sub osc ? does the stair case have a input as
> >listed on the schem ? "staircase in STI" what is this ? i do not know.
>
> STI is the input for the staircase generator. You can either connect it to a
> panel socket, OR hard wire it to the VCO output.
>
> Ken
> _______________________________________________________________________
> Ken Stone sasami@... or sasami@...
> Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
> Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>
>
>
> See the following URLS for the CGS Modular Synth home page:
> Main: http://www.cgs.synth.net/
> Secondary: http://otherunicorn.0catch.com/synth/
>
>
> Yahoo! Groups Sponsor
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--
Dustin

Re: CGS VCO

2005-03-15 by Scott Stites

Hmmm...cake-and-eat-it mode -

If you're a 1/4" or 1/8" kinda guy, you could normal the jack to the VCO
output, allowing the VCO to drive the stepped output. Then, by plugging an
external signal into the jack, you could then drive the stepped output
externally.

Cheerio,
Scott


----- Original Message -----
Show quoted textHide quoted text
From: <sasami@...>
To: <cgs_synth@yahoogroups.com>
Sent: Monday, March 14, 2005 6:37 PM
Subject: Re: [cgs_synth] CGS VCO


>
>
> >pardon my ignorance , what would be use be of connecting it to a jack
> >? would it follow a input signal ?
>
> It would. The signal could for example be from a digital noise generator
or
> an LFO.
>
> Ken
>
> _______________________________________________________________________
> Ken Stone sasami@... or sasami@...
> Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
> Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>
>
>
>
> See the following URLS for the CGS Modular Synth home page:
> Main: http://www.cgs.synth.net/
> Secondary: http://otherunicorn.0catch.com/synth/
> Yahoo! Groups Links
>
>
>
>
>
>
>

Re: CGS VCO

2005-03-15 by dustin sedlacek

ok now this makes sense, i wasnt sure if i was over looking something
on the schem or not im new the diy scene and i appreciate all of the
help from everone , i had another question also ...... 2N4856 where
can i find this ?

Re: CGS VCO

2005-03-15 by mbedtom@aol.com

Dustin,

2N4856A is in stock at Newark Electronics as stock number 13C1994 at $2.06
each. www.Newark.com will get you there. Punch in either 13C1994 or 2N4856
into the "Search For" text box.

A kissin' cousin is the PN4391 (Fairchild) available from Mouser for $0.22
each: www.Mouser.com The 2N4856A is a wee bit faster than the 4391 and has a
wee bit better RDSon figure. The purist in me would say go for the 2N4356 part
but I'd bet you could get away with a PN4391 with no trouble.


As an aside... your name seems familiar to me. Does the address 121 Addison
Avenue (one-way street) mean anything to you? Please reply to that bit
off-list if it does.


Keep the pointy end up!
Tom Farrand


[Non-text portions of this message have been removed]

Re: CGS VCO

2005-03-15 by sasami@hotkey.net.au

>
>ok now this makes sense, i wasnt sure if i was over looking something
>on the schem or not im new the diy scene and i appreciate all of the
>help from everone , i had another question also ...... 2N4856 where
>can i find this ?

There are quite a number of FETs that will work here. 2N4091 installed
backwards is one. Any of the ASM suggested subs will work. Also a MPF102 (or
something like that - I forget the exact number). Basically you want a fast
FET with a low RDS.

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

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