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Tricky octave shifting module
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Wed Apr 18, 2007 3:01 pm    Post subject: Tricky octave shifting module
Subject description: only 2 sockets !
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I wonder if anyone ever need this in a patch, for octave shifting :

Posted Image, might have been reduced in size. Click Image to view fullscreen.

The trick is to generate perfectly-calibrated-voltage sources (1V, 2V or 3) with a standard gate (from 5 to 12volt, no matter)

It's roughly a ken stone’s LED driver, without LED, but with a voltage divider at the output, one for each desired outputs :

http://www.cgs.synth.net/modules/cgsld.html

It can be done without ken triggering circuitry, feeding an analog switch with one of these “quantize” sources, controlled by a gate.

I guess I will put this three little sockets somewhere…

Posted Image, might have been reduced in size. Click Image to view fullscreen.

(when I play arpeggios on my SH I often manually tweak the three-position octave switch on the fly Cool )
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6079smith



Joined: Jan 18, 2007
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PostPosted: Wed Apr 18, 2007 4:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I made this as a module in itself, and I find it great for tuning VCO's. Lots of other uses. Basically adds or subtracts 1 volt from the input. Made a nice front panel and all...
As for multiple outputs (minus 1, minus 2), there's an idea...
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blue hell
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Joined: Apr 03, 2004
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PostPosted: Wed Apr 18, 2007 5:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

6079smith wrote:
I made this as a module i


You posted a link to your G drive .... I can't reach that through it's drive letter Laughing

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Jan
also .. could someone please turn down the thermostat a bit.
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6079smith



Joined: Jan 18, 2007
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Location: Mark of the Dane
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PostPosted: Wed Apr 18, 2007 5:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
You posted a link to your G drive


Gah!
Sorry, not so used to these forum things yet. Here it is. The whole project's been made into a .pdf file now. Worth a look.
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blue hell
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PostPosted: Wed Apr 18, 2007 6:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

6079smith wrote:
Gah!


You'll be a pro in no time Very Happy

Above your posts, on he right side, you'll see an edit button. You can use it to fix old posts, if you want to.

Saw some nice details in the design you posted, like decoupling on the power lines and a 5v1 zener. Good ideas.

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Jan
also .. could someone please turn down the thermostat a bit.
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Uncle Krunkus
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PostPosted: Mon Apr 23, 2007 8:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, very nicely executed project.
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funkyfarm



Joined: Jan 21, 2007
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PostPosted: Fri Apr 27, 2007 7:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Brilliant !

here I've tried to fire 1,00V and 2.00V (connected to VCO CV input) with the CGS Analog Switch Matrix

Once again I hope I've made a mistake (wiring or else) or this module is real shit...

First, when switch is open, about 240mV are present at output. (not a real problem here, just fed the switch with 1.24 and 2.24 volts...)

Then, when all 's fine calibrated, closing one switch have a real bad effect on any other "closed" switch (as back in the old days, your vco ain't stable)

I would call it "gating interference" ; the module is based around a 4066...is this a clue ? or is this a too poor control network ?

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funkyfarm



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PostPosted: Tue May 15, 2007 12:09 pm    Post subject:
Subject description: 4066 IC
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Is 4066 CMOS switch supposed to "click" with audio waveforms (DC for control) ?
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blue hell
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PostPosted: Tue May 15, 2007 12:21 pm    Post subject:
Subject description: 4066 IC
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funkyfarm wrote:
Is 4066 CMOS switch supposed to "click" with audio waveforms (DC for control) ?


Yes ... unless you switch at zero crossings of the signal you'll get clicks.

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Jan
also .. could someone please turn down the thermostat a bit.
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para



Joined: Oct 16, 2006
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PostPosted: Tue May 15, 2007 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

i've had fair luck with adding a 100n for DC offset post switch. its not 100% but it helps a lot.
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funkyfarm



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PostPosted: Tue May 15, 2007 2:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

para wrote:
i've had fair luck with adding a 100n for DC offset post switch. its not 100% but it helps a lot.


Yeep !

Quote:
unless you switch at zero crossings of the signal you'll get clicks.


Can you explain a little further more bit ? I'm afraid I don't understand...
at zero crossings of the signal ?
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blue hell
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PostPosted: Tue May 15, 2007 2:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

funkyfarm wrote:
Can you explain a little further more bit ? I'm afraid I don't understand...
at zero crossings of the signal ?


Yes I did mean the zero crossings of the signal, but the thing actually is that when you switch from one signal to another and they are not at the same level at that particular moment you'll get a sudden jump in the output voltage. That jump will sound like a click.

The zero level actually is for switching an audio signal on or off at a moment that the current value of the signal is not zero. You'll then get such a jump as well - which is actually the same thing as in the previous paragraph except that one of the signals happens to be zero. So that is a special case of the above.

You could indeed soften the click by using a capacitor after the switch, but that will filter high frequencies out as well - I don't know how bad that would be though for the application you have in mind.

There are ways to avoid the clicks, but that's way more expensive than a simple switch. A cross fader instead of a switch could make it go smooth, but that's a lot more complicated.

Another option could be to wait till both signals have the same value and then make the switch. That one lends itself more for digital audio, as the moment of sameness might never come and you'll want to make the switch then anyway, so you need a timeout to handle that situation.

Hope that helps?

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also .. could someone please turn down the thermostat a bit.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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Uncle Krunkus
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PostPosted: Tue May 15, 2007 4:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

What about if you used the same 4066 and some kind of simple short delay circuit to temporarily switch a cap in for the switching and then switch it out? I'm just thinking out loud here. Actually the switching in of the cap might make more clicking. Sad Oh well, just an idea. Laughing
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