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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)


JH Krautrock CV input mod v2.png
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Cloudstache



Joined: Jul 06, 2017
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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
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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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hububalli



Joined: Feb 15, 2014
Posts: 41
Location: UK

PostPosted: Wed May 20, 2020 6:29 am    Post subject:   Reply with quote  Mark this post and the followings unread

Great idea, not tried the CV mods yet but will do.

I implemented the gain modifications and get much more modular friends levels out of it and it sounds much better.

The only downside I found is when the bypass is activated, the output is very low.

My assumption from the schematic is when the bypass is activated, the input is routed straight through to the output. Since the input gain has been reduced with the modification the bypass output is very low.

Was easily fixed with a little strip board amp but wanted to mention it, in case I have done something wrong Laughing

Thanks,
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jacobsteel



Joined: Jun 21, 2020
Posts: 2
Location: Sweden

PostPosted: Wed Jun 15, 2022 12:31 am    Post subject: CV control, external LED-to-LDR control... Reply with quote  Mark this post and the followings unread

To test CV control quickly I've built a "Vactrol-on-a-String" dongle and a "Universal Driver".

• The Universal Driver (buffer opamp to gaincontrol to diode protected effect transistor + switchable LFO) can drive anything from a solenoid to motors to LEDs
• The Vactrol-on-a-String dongle (LED + LDR shrinkwrapped on a cable) gives a variable resistance with no galvanic connection ( = fewer grounding problems).

I tried this external LDR to a manual input I built into the Krautrock phaser and it worked OK. I did not get good pitch to phasing amount control, but I could get some interesting phasing synced to a beat.

Also, the driver can be split-fed audio and give you a crude envelope follower.

Here's the my Krautrock, https://modwiggler.com/forum/post-3776319.html#p3776319 with more details on the manual-potentiometer add.[img][/img]


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Universal Driver (red box; OP-amp buffer + gain control to diode protected effect transistor + Vactrol-on-a-String)
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jacobsteel



Joined: Jun 21, 2020
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Location: Sweden

PostPosted: Sun Feb 04, 2024 11:42 am    Post subject:
Subject description: ... Krautrock phaser, CV controlled (via vactrol)
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Here's the Krautrock Phaser CV controlled via Vactrol.

Controlling via programmed trigger points turned out a bit better AND adding an envelope between the trigger points and Phaser-control was a must!

Youtube demonstration:
https://www.youtube.com/watch?v=B2v5CDmOsLA

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