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 Forum index » DIY Hardware and Software » Jürgen Haible designs
Krautrock Phaser Mod = Voltage Control Input
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peng



Joined: Feb 23, 2006
Posts: 111
Location: Chicago
Audio files: 2

PostPosted: Fri Mar 17, 2017 12:57 am    Post subject: Krautrock Phaser Mod = Voltage Control Input Reply with quote  Mark this post and the followings unread

I'm assembling a couple Krautrocks and made some mods to it.
Want to share and get feedback from others.
Let me know if you see errors, have better/alternative ideas, etc.

I experimented and found a way to add a proper CV input for phase modulation. The module already runs on voltage control - the LFO and Manual pot put out voltages and are applied to the base of Q1 which controls the lamps. We simply add the additional circuitry and run a wire to the base of Q1.
Not quite that simple because the voltage levels that effect the lamp are between 4V and 12V. Those are approximate and probably change from one module to the next depending on lamps, LDR, etc.
We need to bias our CV input and get the range correct.
The two circuits below do this.

One is Unipolar and the other is Bipolar.
I am using only one and that is the Bipolar version because it adds the most to the module.
Adding the CV mod effects the internal LFO/Amount controls!
Not to a huge degree but...I made note of using a diode to keep them isolated but that won't work for the bipolar version.
The bipolar version is good because you can turn the internal LFO level down low and use the CV pot to change the center frequency up or down.

Other changes -
Modular levels distort the input badly.
I cut the input by using a 100K audio taper pot. A resistor of 100K was attached to the wiper and the other end is attached to the INPUT header.
I needed that 100K resistor to make the pot = unity when at 12 o'clock on the dial. I like having the option of a huge amount of gain because works to suppress the phasing effect. Used with a VCA this is pretty cool.

Another change is the output level. I want these MUCH higher.
I replaced the 22K and 2.4K resistors with 2K resistors.
I read on in a different thread that this may adversely effect the feedback.
I haven't noticed a difference but perhaps I need to scrutinize it more?


Please let me know what you think.
Let me know if you have any suggestions, changes, fixes, ideas, etc.

Thanks,
Phil
(forgive me the small print in the circuit diagram! I will make a PDF version of this for easy reference once I get feedback and make any changes if necessary)


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Cloudstache



Joined: Jul 06, 2017
Posts: 1
Location: USA/Portugal

PostPosted: Thu Jul 06, 2017 9:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks so much! I'm going to try it out...
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peng



Joined: Feb 23, 2006
Posts: 111
Location: Chicago
Audio files: 2

PostPosted: Thu Sep 14, 2017 10:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cloudstache wrote:
Thanks so much! I'm going to try it out...


Awesome!
cheers

The two I built before were for a customer so they are gone.
I need to build one for myself now!
but probably won't happen until 2018.

Post how it goes for you and any changes, suggestions.
I'd love to hear about it.
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