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Funky40
Joined: Sep 24, 2005
Posts: 875
Location: Swiss
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 Posted: Tue Jun 16, 2009 8:18 am Post subject:
Modifying the CGS29 Wave multipliers
Subject description: some questions |
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hi,
i like to use the unused IC2 d:
I make two triangle inputs with attenuator and just omitted the 10NF and the second 100K on the Square input, ( the whole PWM is not on the frontpanel )
those go to a first mixer stage ( IC2a) giving a inverted output, then to the CA3080.
I now like to go from after IC2a to the unused IC2d to invert again.
 should i go after the 100K and make another Mixer stage with feedback resistor,
or should i go bevore the 100K and then making just a common inverter without Feedbackresistor ?
Does it makes a difference ? (exept that i could adjust gainsettings when building with the resistors ) |
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andrewF
Joined: Dec 29, 2006
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Location: australia
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| Posted: Wed Jun 17, 2009 12:37 am Post subject:
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Would you be able to draw a schematic of your idea? can't quite grok it from the description 
cheers |
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Funky40
Joined: Sep 24, 2005
Posts: 875
Location: Swiss
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| Posted: Wed Jun 17, 2009 4:35 am Post subject:
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See the CGS29 Schematics ( edit: well i think i answered it myself )
In the middle left is IC2a.
One way i thought is going out after the 100K ( between the 2 OP amps), and to double the schematic of IC2a ( plus additional 22pF parallel to the Feedbackresistor ).
I call this "mixerstage". I think you call this inverting amplifier.
look on the top right the unused IC2d which i like to use. This is mostly allready a simple inverter.
The second option is to use this, going in on in+ but then without using the 100K after IC2a.
so the options are inverting amplifier vs. simple inverter.
hmm, i think i make a second inverting amplifier,
thank you |
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Serenadi
Joined: Jul 03, 2007
Posts: 89
Location: Germany
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| Posted: Thu Jun 18, 2009 12:57 pm Post subject:
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| Funky40 wrote: | | ...the unused IC2d which i like to use. This is mostly allready a simple inverter. |
hi Funky,
no, it is a voltage follower (non inverting, unity gain) with the input set to ground (pin12).
Get the signal from pin 1 of IC2a (before the 100k - this is - in combination with 220R - a voltage devider used to push down the signal for the 3080).
Then use the same config like IC2a - feedback resistor 100k and a 100k for the input signal to go into pin 13 (-), leave pin 12 at ground.
But - to be honest - I really don't see a reason why to invert the signal.
The multipliers output signal is such different to the input signal, so phase problems are not to expect.
ciao
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Funky40
Joined: Sep 24, 2005
Posts: 875
Location: Swiss
Audio files: 1
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| Posted: Fri Jun 19, 2009 10:56 am Post subject:
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| Serenadi wrote: |
But - to be honest - I really don't see a reason why to invert the signal.
The multipliers output signal is such different to the input signal, so phase problems are not to expect.
ciao
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I thought in some cases it may be better for comparisons to have uninverted signals when setting a unit to Bypass.
Well the module is built, and a very funny behave occours in Bypassmode, see later
| Serenadi wrote: | Get the signal from pin 1 of IC2a (before the 100k - this is - in combination with 220R - a voltage devider used to push down the signal for the 3080).
Then use the same config like IC2a - feedback resistor 100k and a 100k for the input signal to go into pin 13 (-), leave pin 12 at ground.
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I built like this, but took the signal after the 100K.
You say: take the signbal bevore 100K and give a own Feedbackresistor.
well, this migtht make the differenze.
What i have:
The Bypassed sound is a Square, perfect, and double the gain. Is it cause of the 220R ?
and funny thing: with the offset Knob and CV i can modulate this Square.
so in fact i have a perfect Squarewave waveshaper with Pulsewithmodulation with a Gain of around 2.5:1 |
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Funky40
Joined: Sep 24, 2005
Posts: 875
Location: Swiss
Audio files: 1
G2 patch files: 5
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| Posted: Fri Jun 19, 2009 10:57 am Post subject:
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this leads to the question:
could one build as simmple a Squarewave wavefolder with PWM or is this behave becaus eof the ciorcuitry around CA3080 ( more than just 220R ) ? |
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Serenadi
Joined: Jul 03, 2007
Posts: 89
Location: Germany
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| Posted: Fri Jun 19, 2009 12:25 pm Post subject:
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| Funky40 wrote: | | The Bypassed sound is a Square, perfect, and double the gain. Is it cause of the 220R ? |
No.
With the 100k in front, the 220R builds a voltage divider which attenuates the signal to a very small one. The CA3080 can handle very small signals only.
| Funky40 wrote: | and funny thing: with the offset Knob and CV i can modulate this Square.
so in fact i have a perfect Squarewave waveshaper with Pulsewithmodulation with a Gain of around 2.5:1 |
Funny. Indeed.
Not knowing really what you did, but I *think*, you build a "whatever-to-pulse-converter" - a comparator.
The Output of a comparator switches between negative an positiv rail - thats why the amplification.
| Funky40 wrote: | this leads to the question:
could one build as simmple a Squarewave wavefolder with PWM or is this behave becaus eof the ciorcuitry around CA3080 ( more than just 220R ) ? |
See above. It IS very simple to build a PWM circuit. But it's not a wavefolder.
And it has nothing to do with the 3080.
It would be nice if you could make a little drawing of what you did.
To get more into it.
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Funky40
Joined: Sep 24, 2005
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Serenadi
Joined: Jul 03, 2007
Posts: 89
Location: Germany
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| Posted: Fri Jun 19, 2009 11:08 pm Post subject:
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| Funky40 wrote: | finally i did this, see attachment.
the attachmnet is the drawing i got from you. |
I remember vaguely.
Ok, forget my thoughts on comparators and pwm. Seems its not what you did.
| Funky40 wrote: | ... without having the 100K in front of it.
Seems to give radical gain |
Yes.
While gain is given by *feedback res. divided by input res.* and your input resistor is 0 Ohm, you created max gain which results in hard clipping.
With the offset pot you add a dc shift to the input signal. This causes a shift of the clipping point on the timeline and therefore a changing in pulsewidth.
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