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CV keyboard's specific note voltages?
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bigtex



Joined: Mar 30, 2006
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Location: Cupertino, California

PostPosted: Mon Apr 10, 2006 7:49 pm    Post subject: CV keyboard's specific note voltages?
Subject description: looking to make (or rebuild) a simple V/oct keyboard
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I made the mistake of trying to clean my Octave Kitten's keyboard and now it has crapped out on me. I'm thinking of re-mounting the thing in a smaller case anyway, so maybe I could make a smaller keyboard out of simple push buttons.

If I wanted to try to make a very simple push-button CV keyboard, I'd need to know the right voltages for the notes. Does anybody have a good link or info on note frequencies and corresponding voltages? I can't seem to find any info on this, but maybe I'm not looking in the right places.

Also, has anybody ever seen the inside of an Octave Kitten? I'm sure the Cat has the same keyboard build as well. It's this really cheezy thing with wires that touch buss bars as the keys are pushed down. All I did was rub the wires and bars down with alcohol (some notes were scratchy or warbly before) and now every key makes the same note. What?

I should take pictures of it so you'll understand what I mean.
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Blue Hell
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PostPosted: Mon Apr 10, 2006 8:16 pm    Post subject: Re: CV keyboard's specific note voltages?
Subject description: looking to make (or rebuild) a simple V/oct keyboard
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bigtex wrote:
and now every key makes the same note. What?


One of the switches makes permanant contact I guess, should be visible if so.

When I read your descrption correctly you have Kimber Allen key contacts or lookalikes, it's quite easy with those to set the moving wire contact on the wrong side of one of the fixed fires.

Re. the voltages. Its usual is to have 1 Volt per Octave, which means 1/12 of a Volt per semitone. This basically means all resistors are equal and in series. You set the voltage accross the whole series such that each set of 12 has one Volt over it. You'll want to make this tunable. An alternative approach is to make a tunable current source. When you use 100 Ohm resistors (which is typical I guess) the current should be 1 / 1.2 exp 3 or 0.83(repeat 3 indefinitly) mA.

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also .. could someone please turn down the thermostat a bit.
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bigtex



Joined: Mar 30, 2006
Posts: 321
Location: Cupertino, California

PostPosted: Mon Apr 10, 2006 8:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh, right 1/12. Duh. I guess if I had really thought about that I would have figured it out.

Is there a specific voltage that is supposed to correspond to a specific frequency, thought? Like is 440Hz (the A note) exactly 3 volts or something like that? I guess with a tuning knob on a synth it doesn't really matter...

I just found this great resource for the Kitten
http://www.tribalsmile.com/kitten/
so maybe I just need to re-tune it. Or maybe some of the wires are stuck, like you said. I need to take another look at it. It was certainly out of tune and not scaling properly even when it was working. But, hey, it was pretty cheap, too. And it sounds AMAZING.

That 1/12 volt per note thing, being so simple, gives me a great idea for a sequencer. The pencil is hitting the paper!

Hey, thanks for the help.
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bigtex



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PostPosted: Mon Apr 10, 2006 11:33 pm    Post subject: Re: CV keyboard's specific note voltages?
Subject description: looking to make (or rebuild) a simple V/oct keyboard
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Blue Hell wrote:
bigtex wrote:
and now every key makes the same note. What?


One of the switches makes permanant contact I guess, should be visible if so.

When I read your descrption correctly you have Kimber Allen key contacts or lookalikes, it's quite easy with those to set the moving wire contact on the wrong side of one of the fixed fires.


I should probably post this on a board more dedicated to vintage keyboards and their repair, but you seem to know a little about this.

Here are some pictures of the keyboard mechanism.

http://www.flickr.com/photos/57919133@N00/tags/keyboard/

Sorry that they are a little dark, but you should get the idea. Each key has a 3x3 grid of holes in the plunger part that goes down. The two wires are inserted into opposite corners, so one is high and one is low. Both are normally not in contact with the keyboard, and I think they are supposed to both make contact with their respective bus bars at the same time. By "bus bars" I mean the thicker, stationary wires.

Any idea how this is actually working? I see the voltage divider network of resistors of equal value. They are all 1k (brown, black, orange). There are some SIP packages that I assume are capacitors for debouncing the switches. It looks like that's it. I don't understand how the keys could be making the same pitch tone if there would be a different voltage at each key's wires.

Do you know how these work?
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ian-s



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PostPosted: Tue Apr 11, 2006 4:15 am    Post subject: Reply with quote  Mark this post and the followings unread

If one of the cv contacts is stuck, then the keyboard should still work above or below the stuck key, but the pitch will jump back to the stuck one. The resister chain should be at some +V at one end, ground at the other. Closing a switch will form a divider and give a +V on the bus. There will also be some additional circuit before the CV gets to the VCO, a sample and hold is used to keep the CV at a constant level so the pitch wont drop on sounds with a long release.

The first thing I would check are any connections between the KBD and main PCB. Look for loose wires.
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bigtex



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PostPosted: Tue Apr 11, 2006 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

g2ian wrote:
If one of the cv contacts is stuck, then the keyboard should still work above or below the stuck key, but the pitch will jump back to the stuck one.


I think I understand what it is doing now. When all of the keys were making the same pitch, it was because only the gate wire was getting triggered. After adjusting more of the key wires, I've discovered that the pitch scaling is now way off, with the difference between keys being much more than 1/12 of an octave.

I'm at work now, but when I get home I'll try to finish readjusting all of the key wires, and then re-tune the keyboard.

Thanks for the suggestions!
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Blue Hell
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PostPosted: Tue Apr 11, 2006 11:59 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm glad you found a cause. The keyboard is not quite what I had in mind, I thought you'd have switches like the ones pictured here Funny during the day I watched the pics on a CRT and couldn't make much from it, on this LCD it's much better.

Got the pic from http://www.kimberallen.8m.net/photo.html

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also .. could someone please turn down the thermostat a bit.
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elektro80
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PostPosted: Tue Apr 11, 2006 12:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is the one, isn´t it?


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bigtex



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PostPosted: Tue Apr 11, 2006 12:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

That does look somewhat similar, though mine only has two wires per key. It certainly is an interesting mechanism.

The problem, though, at least on mine on mine, is that the wires bend a little over time. This puts them out of position, so some will only hit the trigger wire and not the CV wire, or some will just barely hit the CV wire, so the response is kind of wonky.

All I can really do to fix it is try bending the wires around until they happen to be *just right* to hit the keys the right way. Pretty frustrating to adjust, especially on a keyboard that is approaching 30 years old. Plus, they're close enough together that I sometimes hit other wires trying to get to one.

Oh well. I'll eventually get it working.
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Blue Hell
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PostPosted: Tue Apr 11, 2006 12:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

elektro80 wrote:
This is the one, isn´t it?


Hey, yes, but, but where did it go, I mean I had it in my post Question Question

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also .. could someone please turn down the thermostat a bit.
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PostPosted: Tue Apr 11, 2006 1:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

That hosting service does not like deep linking. Very Happy
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PostPosted: Tue Apr 11, 2006 1:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmm, it could have figured that out when I did the preview Evil or Very Mad
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PostPosted: Tue Apr 11, 2006 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

You probably already had a page from that site open in the background or the site had your cookie in the jar or something.
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PostPosted: Tue Apr 11, 2006 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Actually, your image did show up for a few hours before it dissapeared...
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PostPosted: Tue Apr 11, 2006 1:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmm.. a matter of timed exposure? Shocked
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