vco optional octave switch

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Widy75
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vco optional octave switch

Post by Widy75 » Wed Feb 27, 2013 2:07 pm

hi

introduction :)
im new to this forum :) ( first post ) however i'm planing/building a smale okley system ..... but i have some questions ... one for now:

is it possible to exchange one Tune Poti with a octave switch ( e.g octave switch from elby design ) just a rotary with generates 0 - 8 V in 1V steps

Is the Tune Poti just a poti with is connected to 0 and 10 V and generates the input voltages for the freq... if that is so i can do a octave switch instead

or is it possible to add another flying resistor to the sum input of freq cv control to get another control input :)

normaly i can find out such stuff by myself but i did not own the pcb yet and i need to think about this during panel layout design ( i build panels by my own in 3he ) because for the octa switch i need some extra space

lg widy

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sonicwarrior
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Re: vco optional octave switch

Post by sonicwarrior » Wed Feb 27, 2013 2:34 pm

A coarse tune poti is always a variable voltage divider so: Yes, you can replace it with a 'stepped' switch (with several resistors instead of a poti), e.g. an octave switch.

In fact: You can always replace potis with a switch made with resistors. Even if the resistors are unselected 1% that is more precise than a poti. Selected ones are used for mastering equipment to get a precise stereo signal and reproducable values for EQs, compressors and maybe other stuff.
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Synthbuilder
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Post by Synthbuilder » Thu Feb 28, 2013 5:08 am

The coarse pot is actually slung between the +10V and -10V reference voltages. But you could easily use a rotary switch with 0.1% resistors to make an octave switch. I would use +10V and ground as the resistor chain end points. Octave trimming can simply be done by fine tuning the +10V reference voltage with the PSU trimmer on the board.

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jack multiple
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Post by jack multiple » Tue Apr 02, 2013 11:48 am

i'd really like to just carry this on a bit just to learn more stuff.

you say that the tune pot is basically a variable voltage divider and can be changed into a stepped divider by using a switch.

could u or how could you take it further and make it a variable stepped divider using a pot or rotary switch, where each step was an exact semitone?

i have no desire to do this, merely interested . thx

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Dr. Sketch-n-Etch
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Post by Dr. Sketch-n-Etch » Tue Apr 02, 2013 11:38 pm

I just built ianross a 12-position octave switch which generates voltages from 0 to 11V in 1-V steps. I built several of these for myself and Danjel from Intellijel for calibrating Dixies and Rubicons. For Ian, I put the whole thing behind an 8hp euro panel with some very basic graphics. Sorry, I never snapped a picture of it, but it turned out rather well, I thought. It has a hole in the panel for inserting a screwdriver for calibration.

The hardest part of building these is finding a dozen or so matched resistors. In my case, I buy 100 1% 30k resistors on a tape, and then sit in front of the TV and measure each and every one with a DVM. I make a little mark on the tape next to every one which is within 0.1% of the stated value, and then use those for the switcher. For the switch, I use a 24-mm Alpha switch. It is pretty high-quality, and very nice to wiggle.
Last edited by Dr. Sketch-n-Etch on Tue Apr 02, 2013 11:43 pm, edited 1 time in total.
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Dr. Sketch-n-Etch
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Post by Dr. Sketch-n-Etch » Tue Apr 02, 2013 11:43 pm

...Here's a graphic of what the stuffed PCB looks like:

Image

That stuff on the right is where the jack is attached.
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jack multiple
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Post by jack multiple » Wed Apr 03, 2013 8:10 am

that looks pretty interesting.
i want to at some point , when i understand it all a bit more, to put something like that on an analog sequencer in place of the normal cv outs .calibrated to 1 semitone per step, think it would be great, with a separate octave swich by each one.

anyway, going to copy that diagram into my list of 10 billion things i dont understand, then pull it out when i do. thx

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