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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS35 - 47K output resistor
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Flareless



Joined: Jan 16, 2016
Posts: 20
Location: Ontario, Canada

PostPosted: Fri Mar 11, 2016 6:45 am    Post subject: CGS35 - 47K output resistor Reply with quote  Mark this post and the followings unread

Quick question;

In Ken's documentation of the CGS35 he states that if fitting the output level with a potentiometer "The associated 47K resistor can be replaced with a link". Does this mean it SHOULD be replaced with a link? Is there any benefit to using a link versus a resistor?

Since I plan to use a potentiometer for the output level I thought I should figure out my course of action before soldering.

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wackelpeter



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PostPosted: Fri Mar 11, 2016 11:44 am    Post subject: Reply with quote  Mark this post and the followings unread

i would omit the output potentiometer and therefore add attentuators for the input signals...

The 47k can be ommited and a link instead can be used... with a link you will have less gain at the output... at least the higher the resistance in the feedback path of the op amp is the more gain you have...

Well when self oscillating this thing can become very loud... maybe you just paly a bit around with it... until you find what suits your tastes... perhaps it's a good idea to keep a back door open to add an output pot afterwards or if you don't add attentuators for the inputs first some spare room to add them later on...

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Flareless



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PostPosted: Sat Mar 12, 2016 5:24 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
i would omit the output potentiometer and therefore add attentuators for the input signals...

The 47k can be ommited and a link instead can be used... with a link you will have less gain at the output... at least the higher the resistance in the feedback path of the op amp is the more gain you have...

Well when self oscillating this thing can become very loud... maybe you just paly a bit around with it... until you find what suits your tastes... perhaps it's a good idea to keep a back door open to add an output pot afterwards or if you don't add attentuators for the inputs first some spare room to add them later on...


Thank you for the tips WP! I've been looking around at various configurations of this board and I had a few more questions. I apologize if they are a bit naive but I'm still a beginner when it comes to electronics;

- In order to put attenuators on the audio inputs can I just replace the 47K resistors with variable resistors. Are 50K pots ok to use? Should they be linear or log?

- I would like to put a level potentiometer on the CV In. Can I replace the 220K resistor with a potentiometer to do this? If so what is the recommended value and should it be linear or log?

- I have seen some designs with an "All Pass" input. Can the CGS35 be modified to use this input?

Finally....

- Is there a wiring diagram available for these modifications? I have been searching all over yet can't seem to find one.

Sorry again for all the questions... I'm still learning Embarassed

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wackelpeter



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PostPosted: Sat Mar 12, 2016 9:08 am    Post subject: Reply with quote  Mark this post and the followings unread

When you will attentuate the input signals you should not remove the original input resistors but add a pot with wiper to that resistor one outer lug goes to gnd and the other to the signal input...

For audio signals i would use log and for CV lin pots... but it's not necessary to have log pots for the audio input... only because the human hearig is more close to a log response...

A good advice is to look over at Ken's other Steiner VCF design or Yves Yusson's design.... i've built both of these designs and i'm happy with them, liking the Yusynth Steiner VCF a bit more...
http://www.yusynth.net/Modular/EN/STEINERVCF/index-v2.html
http://www.cgs.synth.net/modules/cgs35_euro_vcf.html

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Flareless



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PostPosted: Sat Mar 12, 2016 1:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you for the tips! I will try them out and see what happens.
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