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 Forum index » DIY Hardware and Software » Circuit Bending
Augmentations for Casio MT65 Keyboard
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gasboss775



Joined: Jan 02, 2016
Posts: 188
Location: Scotland

PostPosted: Thu May 04, 2017 12:55 am    Post subject: Augmentations for Casio MT65 Keyboard Reply with quote  Mark this post and the followings unread

I acquired a Casio MT65 "toy" keyboard as a result of my eldest daughter clearing out her room.

It's actually not bad for a toy. However I did think that it could be improved upon. So far the following circuits have only been breadboarded, but they do work.

First up, Goschillator filter circuit. .

Modulated clipper circuit.

PWM circuit


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gasboss775



Joined: Jan 02, 2016
Posts: 188
Location: Scotland

PostPosted: Fri May 05, 2017 11:41 am    Post subject: LM13700 VCF Reply with quote  Mark this post and the followings unread

I tried the following VCF in conjunction with the envelope follower circuit in the other circuits


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gasboss775



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Posts: 188
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PostPosted: Fri May 05, 2017 3:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is the support circuitry for the above VCF, thought I should post it as there were some variations from the original posted circuits in my first post.


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gasboss775



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PostPosted: Mon May 08, 2017 5:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Yesterday I built another VCF to try with my Casio MT65 keyboard. It was based on a circuit by Eric Archer, that can be found, here:

9V Lowpass VCF

I had trouble getting his expo converter to work even with a rail to rail CMOS opamp ( lmc6482 ) Anyway I devised an alternative converter that can work with a cheap and simple lm358 with a single +12 V supply. I suspect it could work on lower but then I think a rail to rail opamp would become necessary, I try to avoid them as they are so much more expensive than regular opamp.

The circuit worked very well and actually produced some respectable sounds.

Here is the schematic of the VCF


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PHOBoS



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PostPosted: Mon May 08, 2017 5:58 am    Post subject: Reply with quote  Mark this post and the followings unread

ah, the good old Eric Archer LPF. I still have one laying around here which I am thinking of putting in a box with some other circuits
I have. So this thread is inspirational Very Happy I build mine with a TL072 TLC2262CP and didn't encounter any problems, or at least it sounds great. I
also used an opamp for the fake GND.

Since you already have a squared up version of the signal you could put the CD4026 with an R2R in there as a suboscillator.
It would only take 1 chip and a couple of resistors (and a mixer I guess).
(in case you missed it I posted a track in which I used it here and the patch here)

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Last edited by PHOBoS on Tue May 09, 2017 3:22 pm; edited 1 time in total
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gasboss775



Joined: Jan 02, 2016
Posts: 188
Location: Scotland

PostPosted: Tue May 09, 2017 11:49 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
ah, the good old Eric Archer LPF. I still have one laying around here which I am thinking of putting in a box with some other circuits
I have. So this thread is inspirational Very Happy I build mine with a TL072 and didn't encounter any problems, or at least it sounds great. I
also used an opamp for the fake GND.


I also used an opamp for the fake ground. I think the problem was messy construction on a breadboard, anyway I knew that the other circuit worked well with the lm13700, provided you're not too fussy about volt per octave tracking or temperature drift!

Quote:
Since you already have a squared up version of the signal you could put the CD4026 with an R2R in there as a suboscillator.
It would only take 1 chip and a couple of resistors (and a mixer I guess).
(in case you missed it I posted a track in which I used it here and the patch here)


What I would really like is some kind of circuit to track the pitch of the signal from the keyboard. I was planning on trying some counters on the squared up signal. I also tried a guitar octaver circuit and this worked quite well.

PHOBoS I'll be sure to listen to your track later, I don't have my headphones at the moment.

I have attached the Octaver circuit that I tried.

Original Green Ringer Schematic


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PHOBoS



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PostPosted: Tue May 09, 2017 3:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

oops Embarassed I took a closer look at the opamp and I actually used a TLC2262CP. It had collected some dust over
the time it has been laying around here and I only took a quick glance. Had no idea I actually used a rail-to-rail opamp.

what exactly do you mean by tracking pitch, something that isn't a squarewave ? I assume that by squaring up the signal you
pretty much have something that tracks pitch. A divider might clean it up a bit though. The 4046 can also be used as a pitch
tracker but it is mostly fun when it fails doing that correctly Laughing

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gasboss775



Joined: Jan 02, 2016
Posts: 188
Location: Scotland

PostPosted: Tue May 09, 2017 3:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
oops Embarassed I took a closer look at the opamp and I actually used a TLC2262CP. It had collected some dust over
the time it has been laying around here and I only took a quick glance. Had no idea I actually used a rail-to-rail opamp.

what exactly do you mean by tracking pitch, something that isn't a squarewave ? I assume that by squaring up the signal you
pretty much have something that tracks pitch. A divider might clean it up a bit though. The 4046 can also be used as a pitch
tracker but it is mostly fun when it fails doing that correctly Laughing


I was thinking about something that could generate a control voltage, that in turn could be fed to several oscillators for the creation of a much bigger sound.
I do in fact have something in mind that might do the trick. It was a DIY guitar fx unit from a really old electronics mag ( 1987 I think ) the idea was for an oscillator to track the guitar then the output of the oscillator was combined with the guitar signal using a ring modulator. The title of the project was "
Light Metal Effects" anyway I was thinking of trying this to see how well it would track the Casio keyboard.

I had wondered about the 4046 too, didn't you post something like that before?
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