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 Forum index » DIY Hardware and Software » Jürgen Haible designs
Switching jacks in JH designs
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numbernone



Joined: Aug 16, 2006
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Location: new york city

PostPosted: Wed Apr 14, 2010 10:22 am    Post subject: Switching jacks in JH designs Reply with quote  Mark this post and the followings unread

I am planning to incorporate a bunch of JH stuff into a standalone unit, and have a pretty general question that might apply to lots of other things as well.

Many of the jacks are of the switching style, often times closed to ground. As I am going to be using bananas, I am wondering where this might present a problem? Should I expect some instability if I leave an input hanging ungrounded? I would really hate to have to add a ton of extra switches to something like the Filter/Phaser as it already has so many.

Thanks!
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The Peasant



Joined: Nov 13, 2009
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PostPosted: Thu Apr 15, 2010 1:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've built the Living VCOs, Filter/Phaser, Tau Phaser, Polymoog Resonator, and Solina Chorus without switching any inputs to ground, and they all seem to work fine for me.

Take care,
Doug

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jhaible



Joined: May 25, 2007
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PostPosted: Fri Apr 16, 2010 12:46 am    Post subject: Reply with quote  Mark this post and the followings unread

The Peasant wrote:
I've built the Living VCOs, Filter/Phaser, Tau Phaser, Polymoog Resonator, and Solina Chorus without switching any inputs to ground, and they all seem to work fine for me.

Take care,
Doug


I never tried to leave things open, but with reasonable lenght of wires I don't expect a problem.

There are a few exceptions, though.
Sometimes I have LFO rate and depth CV inputs that allow the connection of a simple (passive) potentiometer as an alternative for applying a control voltage. Don't ask me *which* inputs on *what* modules that applies to (I would have to go thru all schemos again, myself); but you can easily detect this from a "pullup" resistor of 100k or 200k or something like that, connected from the input to +15V. The idea is that connecting a variable resistor (potentiometer) to the jack, the CV is created right in place. And for CV = 0 you need Resistance = 0, so normalizing the input to GND via the switch contact is what I did.
If you don't need that function, or if it gets in your way with banana jacks, simply omit the pullup resistor.

Jh.

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