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Installing a pitchbend wheel into a Casiotone 501


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Hey guys,

Haven't been on in ages, hope everyone is well. I have a casiotone 501 laying around in good working order, but I want to try and put a pitchbend wheel into it. For those that don't know the Casiotone 501, its the same as the one in this pic:


The reason I think this is possible is that the keyboard has a master tune pot on the back, which really works in the same way....its not a MASSIVE swing in pitch (im guessing a major 2nd at MOST....probably only a half step even) but its better than nothing, and still helps breathe a bit of life into the dorky sounds it makes.

I bought one of the following: http://www.analoguehaven.com/doepfer/spareparts/modwheel/ with the intention of installing that and re-wiring master tune pot to the mod wheel pot instead. This is where a few issues come into play however.

Those that remember my posts from about a year ago may remember...I am not a wizz with electronics :) I THINK (its hard to access the back of it to read clearly) that the master tune pot is 100K value...and I would assume it would be linear.

The mod wheel comes with a 10K linear pot...but to make calculations more confusing...the mod wheel, through its' entire sweep, goes about 40% of the pots full sweep.

So I guess my main question is...how can I get it set up so a pot that is only using 40% of its sweep distance, is giving the same resistance (in that 40%) as a 100k pot's entire spectrum of resistance? I figure I will have to probably make another little pcb with other components to modify the current before/after it goes through the pitchbend pot yes?

Any advice greatly appreciated! :)

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With a 10k pot that only uses a part of it's range you won't be able to directly model a 100k pot. It might be extremely helpful to know what the original pot is actually doing - any chance you have a schem/service manual for the CT-501? Judging by my quick 3-minute google-search, there's not a lot of info on the net about the CT-501...

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Here's a ghetto fix for you...

You should be able to replace the pot in the pitch bend to something larger. Let's assume the master tune pot is really 100K. You want something that has 100K in 40% of the pitch bend wheel sweep, so 250K linear pot.

Now you can open up the pot, there'll be a resistive strip, an arc of carbon paint with a wiper on it. You can then (somehow) "short" the 30% on either side of the middle 40%... make that part of the strip very low resistance. It might take a bit of trial and error to get it working correctly, and maybe you need to tweak the "middle" position of the pot relative to the pitch wheel mid point (where it springs back to)... but it should work, and is pretty cheap

Check this out:


you can bridge over breaks in the resistive material with copper or silver conductive paint, or make a custom tap point

OK now that would be the 1:1 solution... a pseudo-100K pot in a pitch wheel. However, if it really is a linear pot, it might just be being used as a voltage divider and some other trick might work better.

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OK, so maybe I'm thinking about a different way to do this..

instead of hacking up the original electronics, how about building this as a midi controller?

Set up your new stick to send 14 bit Pitch Wheel commands..

Add an extra smaller control to send RPN Messages to set the total pitch range,

and leave an open channel or two for a Modulation Wheel if you want to add that later.

You could do this all on an 8 bit core without any additional modules, once it's tested you could then build it into the Casio case or keep it separate, and as a bonus, you can test it all in advance before you build the first thing just by sending the appropriate MIDI commands for your PC to see how well the Casio handles it.

This just seems easier than trying to reverse-engineer the Casio tuning system. :)

Have Fun,


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Hey guys, I wasn't specifically saying I was going to use the 10K pot that came with the pitchbend wheel...I was just saying that that is its value :) I have no problems changing it to something else...I mean...obviously I could put a 100k pot in there...but it would only be bending +/- 5 cents or so...not really enough to be useful.

And to lylehaze, the keyboard has no MIDI capabilities, and I am not interested in giving it any....just keen to try and expand its functions in an easy way (ie. pitchbend) Thanks for the help so far guys! I will try and get a closer look at what the standard master tune pot is...I would ASSUME for something like that, where the value is increasing at a set rate...it would surely be linear yes?

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No Midi?? WTF?

Wrong Forum.. try "NOMIDIBox.org".. or maybe "WeDontNeedNoStinkingMIDI.com"

They have a great article on making rhythm patterns by banging rocks together. :)

But seriously.. there are very reliable ways to pitch bend without modifying the electronics.

Google up on "Doppler Effect". You can change the pitch of your keyboard higher by moving it towards your listeners, or lower by moving it away from them. So you can work up a great solo riff, and for the big "pitch bend" climax just throw your Casio at the crowd. The faster you throw it, the higher the pitch bend will be!

Hey, physics CAN be entertaining! :)

Have Fun,


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  • 2 months later...

Hi All,

I was searching for info on the Casiotone 501, and found this thread.

I bought a 501 new, way back when (1980?) and still have it. As I write this, my kids are playing it right next to me!

The MS jack on the rear panel, a 5-pin DIN, is for a barcode scanner. There were song books available back then, with barcodes instead of standard music notation, and you would use the barcode to scan in the song. Once scanned in, you could sit back and listen to it play, or use the "melody guide" (a position on one of the switches). The melody guide would light up an led (red for white keys and green for black) which correspponded to the next note to be played. The keyboard would not let you continue until you pressed the key under the LED, and no other key would sound.

There were accessory pedals available for volume and sustain, but I didn't buy them.

At the time I purchased this unit, there was also a 701 available, which was much larger, with more keys. As I recall the price was quite a bit more, so I settled on the 501.

Somewhere I have the service manual for this unit, though I don't know if I could find it easily. If anyone cares, I'll look for it.

I also have the scanner and some books somewhere, too. I'll see if I can dig them up, and post some pics.


Edited by alleyandy
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