Finished Pieces

Casio SA keyboards

    Casio SA Keyboard Modification.

    I got an email from Jeff Stonestreet the other day with an attached schematic.
    “Attached is a schematic I created for the Casio SA-7 keyboard. I am working on a microprocessor-controlled sound generator and plan on using the SA-7 for parts. I got frustrated trying to figure out how the thing was wired, so I finally spent about a week carefully mapping every circuit board trace.
    Maybe the schematic will save others the same frustration!”

    Thanks Jeff!

    This is an engineered modification which works on most of the Casio SA series ( SA-1, SA-5, SA-7, SA-8 etc). There will be an Amplifier chip ( No AN8053 ) common across the SA series and a mask programmed CPU which will be made by OKI and have the part No M6387-xx where xx is the variant for the specific keyboard it is installed in, in the case of the SA-5 it is M6387-16. The different variant number accommodates different key / button layouts of the keyboard it is fitted into, the PCM sounds however remain the same. There are 5 interesting modifications that can be easily fitted:

    1) Pitch Shifting
    2) Power Crash
    3) 5th’s Switch
    4) Glitch Randomizer
    5) Filter/ Feedback Adjustment

    1) Pitch shifting. The CPU runs at a fixed speed of 22Mhz which it needs to create the internal sounds out of its Rom and to run the main program that scans the keyboard / buttons and plays the sounds. It has to run at a precise fixed speed as a lot of the internal processes are calculated by dividing the clock signal internally. It is not possible to just remove the Casio’s crystal and swap it with another, as the original crystal has 3 legs, and most others have 2. In order for the crystal to oscillate it needs two capacitors, these are built into the original crystal and come out on the 3rd pin in the middle. To successfully swap the crystal we need to add two 22pf ( very tiny ) capacitors to a new crystal and complete the oscillator circuit. I have got it to run as low as 6Mhz but at this speed it executes it’s system program slower also, so there is a tiny delay after switch on before the keyboard responds.. this is normal! It is also possible (although I have not tried) to increase the clock speed and put a 30Mhz crystal in, which would increase the pitch of the keyboard.. it may even go higher, just like overclocking your PC!

    2) Power Crash. The CPU needs a stable regulated voltage to run normally. If a variable resistor is put in series with the supply to the keyboard (removing the DC in Jack off the PCB and using the solder pads works very well) it will reduce the available voltage the CPU can use, and there is a threshold where the CPU does not have enough power to run correctly, but it has enough to not stop, this causes random sounds.. glitches in playback etc. Different results are achieved if the speaker is removed or not as the speaker requires a lot of power to run, the CPU does not glitch out as much with it in circuit, it just gets quieter when the power is reduced. A good value potentiometer is 500 ohm, which maybe hard to get but can be made with a 1K pot with a 1K resistor in parallel, giving a 500 ohm potentiometer

    3) 5th’s Switch. When you play a key, activating this mod will play a second note at the same time, either a 5th up or down depending on the position of the toggle (centre off toggle switch needed). This mod simply fools the CPU into thinking an extra key is pressed. All the keys are wired in a sort of X Y matrix that the CPU scans the X and the Y lines to see if a key or button is pressed. By shorting out an extra line, when the key is pressed the CPU sees 2 key presses and plays 2 notes. The switch is wired to short out either 1 line up or 1 line down of the line that scans the keyboard. It may not work on all the SA series as the CPU is configured to scan different button arrangements on different models, these pins may connect to buttons rather than keys on a different model.

    4) Glitch randomiser. This causes a random effect on the CPU dependant on how the knob is set, and what the keyboard is doing at the time. I previously mentioned that the CPU constantly scans all the keys and buttons.. This mod takes the final amplified audio signal out of pin 5 of the amplifier chip and injects it back into the scanning matrix via a 1Meg pot. Instead of the CPU seeing a definite signal (such as when a key is pressed) it doesn’t know what to do when it finds a much amplified audio signal where it is expecting a scan signal, and it locks the CPU up. If the keyboard is idle and not making any sound, then turning the knob has no effect as there is no audio signal there to inject back into the CPU.

    5) Filter / Feedback pot. This works exactly the same way as sticking a live microphone in front of an amplifier speaker and you get howl or the Larssen effect ( usually heard at drunken speeches – or after dinner events ). The modification takes the audio output frm the amplifier which is quite large, and injects it back to the CPU output that is connected to the input of the amplifier chip, which then amplifies it further, feeds it back and amplifies it more.. the amplifier chip cannot cope and goes into self oscillation which is heard when the knob is wound right up. The Potentiometer used is a 1K pot, but a trimmer is also fitted in the 1 leg, so with the pot turned right down there is still some resistance between the input and output of the amplifier, otherwise it would feedback all the time. When setting up, adjust the trimmer so that oscillation starts approximately 1/3 of turning the main 1K potentiometer. When the amplifier is in self oscillation / howling, it draws a relatively large amount of power, which causes the power glitch mod to not work properly, it is better to put a switch between the 1K potentiometer and the wire to pin 5 of the amplifier chip, so the feedback loop can be broken

    There are further potential modifications, such as Rheed’s body contacts and instability pot.. these both work on the Crystal oscillator circuit, and cause the CPU to miss a clock pulse causing a crash in the internal program. The same effect can be achieved by switching the clock speed, as the time it takes for the switch to disconnect one crystal and connect the other by moving the lever, may only be a fraction of a second for us, the CPU has missed literally thousands of clock pulses and doesn’t know where it is in it’s program. Very occasionally I have managed to play a note, flip the switch and it continues to play but dropped in pitch 99% of the time it will crash the CPU.. the most spectacular results occur if you have the power reduction pot right on the threshold, where the SA is fighting to make sense of what is going on, and then you change the crystal.. utter mayhem :)

    P.Parry Aka OCEANUS 15/1/08


    46 Responses to “Casio SA keyboards”

    • 1

      PlasticAnimal said:
      January 26th, 2010 at 12:17am #

      Hi, I’ve found a similar bend as the filter/feedback on the sk-1. It sounds great and gives chord mode some insane bass. The only problem (besides loss of polyphony in normal play) is that after a while you get a lot of lo-fi distortion and some drop in volume. It seems like it clears up if I leave it off for awhile. I’d love to fix this though. Any ideas?

    • 2

      casper said:
      February 18th, 2010 at 1:05am #

      @PlasticAnimal: It’s pretty hard to say what is going on there. Generally any effect that changes noticeably over time is to be avoided. Safe effects will be the same no matter what. Some effects will change as the battery dies, but other than that be careful of changing effects.
      Something I like to do is use a current meter on the power supply. Then when I hook up potentially dangerous bends like the one you’re talking about I can see if it pulls lots of power. If it does, then it’s no good.

    • 3

      PHOBoS said:
      March 19th, 2010 at 4:19pm #

      Thanx for sharing this information! I recently did a SA-8 bent, but with this information I can add some more modifications. =)

      I just got myself a second one today, so I’ll probably leave the first one as it is and start working on the that one. (Have you ever tried bending 2 keyboards by making connection between them ?)

    • 4

      AWAKE said:
      March 30th, 2010 at 10:12am #

      Hmmm… I have done the crystal swap, but with no luck. I had a few 6Mhz crystals and ordered 22pf caps, built the circuit, checked it thrice, and nothing. It just won’t come on when the switch to the 6Mhz crystal is flipped. It turns it off and the unit won’t power up when the alternate crystal is selected.

      I have made it go into a crazy oscillation followed by a spectacular crash…once. Any ideas?

      The 5ths switch is brilliant!

      Keep up the fine work sir.

    • 5

      casper said:
      April 11th, 2010 at 12:40pm #

      You don’t actually HAVE to remove the power jack to install the crash knob. I think the better way to do it is to cut the lead coming from the jack then installing the adjustment on both sides of the cut. The crash will work best when the keyboard is battery powered. It probably won’t work when you use a power adapter.

      I’ve never worked on the SA-40 but the SA-X bends will probably work.

    • 6

      casper said:
      April 11th, 2010 at 12:43pm #

      @PHOBoS: Yes I’ve done some cross bending between 2 keyboards. It’s worth trying. Sometimes it awesome and sometimes it’s not. IT works best if you connect the ground of both keyboards or if they share the same power supply.

    • 7

      casper said:
      April 11th, 2010 at 12:46pm #

      @AWAKE:I’ve heard from a few folks lately who are having similar problems. I’ve actually never tried the crystal swap. Most of the bends in the diagram were supplied by a bender named OCEANUS. I’ll try it out and see what happens.

    • 8

      yto said:
      May 31st, 2010 at 10:46pm #


    • 9

      PHOBoS said:
      June 21st, 2010 at 2:33pm #

      After doing some other things I returned to my SA-8, and have some info I’d like to share. I draw a comnplete schematic of the circuit to get a better understanding which clearly showed some unused connections in the button matrix. Adding these buttons gives you 75! extra sounds (so all the sounds from the SA-1), 3 more demo’s and a cowbell. There are still a couple of connections which don’t seem to do anything.

      To get all the SA-1 sounds do the following:
      1) rename the original Tone buttons so the numbers correspond with the ones on the SA-1.
      Tone1 -> Tone0
      Tone2 -> Tone1
      Tone3 -> Tone2
      Tone4 -> Tone3
      Tone5 -> Tone6
      2) add buttons between the following pins of the OKI chip:
      26-15 -> Tone4
      25-11 -> Tone5
      25-13 -> Tone7
      25-14 -> Tone8
      25-15 -> Tone9

      For the 3 extra demo’s add buttons between the following OKI chip pins: 24-15, 24-16, 24-17.

      And if you need more cowbell add a button between pins 23-12 of the OKI chip.

    • 10

      stusvend said:
      July 13th, 2010 at 8:51am #

      Just FYI for everyone, they have several different 500 OHM pots to choose from at Taydaelectronics has some for .40 cents a piece. You can get lower quantities for cheap prices from these places too. No, I dont work there :) HTH

    • 11

      nomad said:
      July 23rd, 2010 at 6:01pm #

      hey all, I’m wondering if you can help me add a volume pot to an sa keyboard.


    • 12

      Ben SImon said:
      July 25th, 2010 at 10:13am #

      hey all, I wondering how to add a volume pot to a sa keyboard.


    • 13

      casper said:
      August 7th, 2010 at 9:27pm #

      @Ben and Nomad:
      Check out my output jack/volume control schematic for some details:

    • 14

      samspike said:
      August 19th, 2010 at 7:28am #

      PHOBoS tips all worked great for me, except one of my additional demos is coming out the same as a pre-existing demo. It’s possible that it’s my wiring that is at fault however.

      I would however propose a variation:

      PHOBoS’s number of the extra sound buttons, keeps the patch numbers the same as the SA-1, but it means the existing buttons on the SA-8 front panel are kind of in a funny order (0,1,2,3,6 with 4,5,7,8,9 somewhere else).

      Instead my suggestion (Yes I’ve tried this) is to keep the existing tone buttons labelled 1 to 5, and label the new buttons 6 to 0, then re-order the SA-1 patch list to match this.

      In other words:

      Tone 1 button stays as tone 1
      Tone 2 button stays as tone 2
      Tone 3 button stays as tone 3
      Tone 4 button stays as tone 4
      Tone 5 button stays as tone 5

      New buttons:

      Tone 6 is a push-to-make button connecting pins 26 and 15 on the OKI
      Tone 7 is a push-to-make button connecting pins 25 and 11 on the OKI
      Tone 8 is a push-to-make button connecting pins 25 and 13 on the OKI
      Tone 9 is a push-to-make button connecting pins 25 and 14 on the OKI
      Tone 0 is a push-to-make button connecting pins 25 and 15 on the OKI

      Now the two digit tone numbers 11,12,13,14,15… upto 55 are unchanged from the descriptions on the original front panel, but the new buttons allow access to the additional sounds.

      The patch list arranged to match this button numbering scheme is:

    • 15

      samspike said:
      August 19th, 2010 at 7:28am #

      01 TRIANGLE
      02 CONGA/AGOGO
      04 TOM
      05 BASS/PIANO
      06 ROCK DRUM
      07 SWING DRUM
      09 PIANO/FLUTE
      10 ACCORDION
      11 PIANO
      12 ELEC PIANO
      15 PIPE ORGAN
      16 JAZZ ORGAN
      17 ELEC ORGAN
      20 CLARINET
      21 BRASS ENS
      22 WARM BRASS
      23 TRUMPET
      24 TUBA
      26 BRASS HIT
      27 WIND ENS
      28 OBOE
      29 BASSOON
      32 WHISTLE
      33 QUENA
      34 FLUTE
      35 BAGPIPE
      36 FLUTE-VIB
      37 OCARINA
      38 HARMONICA
      39 CHORUS
      40 SLAP BASS
      41 STRINGS
      43 VIOLIN
      45 JAZZ GUITAR
      46 CELLO
      47 ELEC GUITAR
      48 MUTE GUITAR
      50 PEARL DROP
      52 FANTASY
      53 WAW VOICE
      56 METAL LEAD
      57 CATHEDRAL
      59 POP LEAD
      60 SHAMISEN
      61 ELEC BASS
      62 WOOD BASS
      63 SNARE BASS
      64 UKULELE
      65 MANDOLIN
      66 BANJO
      67 SITAR
      68 HARP
      70 SYNTH-BASS
      71 SYNTH-PIANO
      73 SYNTH-CLAVI
      75 SYNTH-LEAD
      76 SYNTH-BRASS
      77 SYNTH-REED
      81 AIRPLANE
      82 AMBULANCE
      83 INSECT
      85 TELEPHONE
      86 LASER BEAM
      88 CAR HORN
      90 WADAIKO
      92 MARIMBA
      94 BELLS
      96 GAMELAN
      99 MATSURI

    • 16

      ralf said:
      August 25th, 2010 at 3:41am #

      i’m kinda a newbie in bending, i really wanna get sounds like ‘feedback amplifier chip’, but i’m confused about what kinda mods i should make. can i get that kinde of feedback when i only install that mod? pretty dumb question i guess, but as a non-native english speaker all the technical terms are still a bit difficult.
      so my question is, what should i install for that feedback and what kinda potmeters and stuff should i get. hope somebody wants to help as its a really stupid question i’m affraid :P

    • 17

      oscar said:
      October 17th, 2010 at 12:30pm #

      Hello casper,

      I own a casio SA75 and want to install a pitch mod. it seems to be proving harder than expected. I’ve been told i may need to build my own oscillator? can you o’ mighty electronic wizard shed some much needed light on my current dilema??

      all the best


    • 18

      casper said:
      October 24th, 2010 at 4:40pm #

      Yes you probably do have to build an oscillator. But don’t be afraid!! Once you jump the hurdle of building and integrating circuits, the world of electronic circuit bending madness is yours! sells a pitch control oscillator kit. here it is:

    • 19

      Stephen said:
      October 31st, 2010 at 10:12pm #

      Not exactly a bending question, but any insights on installing an aux out jack?

    • 20

      Nixot said:
      December 6th, 2010 at 5:53pm #


      Remove the speaker and solder the red and white wires to a headphone jack. It’s as simple as that.

      Alternatively, you can also wire the speaker back on parallel to the headphone jack along with a speaker on/off switch, or use a latching headphone jack (which I didn’t, so don’t ask me for details on that).

      Hope that helps!

    • 21

      reckoner said:
      February 24th, 2011 at 5:14pm #

      hi i just did the 5th mod on my sa2 , it works, but just on the first and last octave , the middle section just plays a single tone. do you think this is normal?

    • 22

      extraño said:
      April 14th, 2011 at 2:01pm #

      Hello. That type of pots used in every modification? And if please they might explain it to me of the buttons and the hidden sounds…

    • 23

      Leo said:
      May 18th, 2011 at 11:17am #


      i am currently bending my casio sa-3, but due to old condition, when i pulled the crystal out of the circuit, the legs are broken, mostly eaten up by rust,

      any solution? could it be replaced with another crystal?

      or should i get another sa series?

      Thanks before

    • 24

      Aidan said:
      June 2nd, 2011 at 6:53pm #

      Hi. i plan to start making a keytar out of one of the New series Casio SA’s in the coming weeks, and i plan to put some pitch up/down body contacts on the neck. just some note-bending effects to add to my solos. I was wondering ahead of time if the Newer series Casio SA’s could be bent

    • 25

      Pudan said:
      June 10th, 2011 at 7:00am #

      There is a better glitch randomization than the one in the schematic, and that is to manipulate with the crystal directly. My object was a SA-21 which have the same circuits. I did not do the “pitch shift” as I didn’t have another crystal, but I could confuse the cpu in wonderful ways by interrupting the clock pulses from the crystal, by brief shortcircuiting of the crystals legs to nearby components. It’s worth experimenting with.

      Also, I cound not get the power crash to work on the SA-21, even with a 500 ohm pot and without the speakers. But the feedback loop and the 5ths mod is great.

    • 26

      Steve Nibbs said:
      July 16th, 2011 at 7:55pm #

      The MD 2 is one pretty bad ass pedal…

    • 27

      Hans said:
      July 17th, 2011 at 8:40am #

      @reckoner, i did the 5ths thing on an m100(equals sa-5) and it didnt work on every key. just about half of them

    • 28

      das data said:
      January 3rd, 2012 at 11:37am #

      Dear humans, presumably,
      could anyone help me get a manual for the Casio SA-3, please?? Would be nice…thanks in advance, Evelien (das data Rotterdam the Netherlands)

    • 29

      Rolbista said:
      February 9th, 2012 at 5:59pm #

      what are relations between crystal’s frequency and pitch? What i mean is if I put, say, an 11Mhz crystal for switching, or even 5,5Mhz crystal for switching, would the whole sound go down one and two octaves down? Maybe that’s a silly question, but two different crystals wouldn’t be blendable to get gradual pitch shift, would they? Also, more than in oscillation, i’m interested in distortion and saturation of the signal, is the feedback mod good for this? I suppose I would need to adjust the trimpot differently then, right?

    • 30

      casper said:
      February 10th, 2012 at 1:12pm #

      The crystal frequency sets the clock speed of the whole circuit. Clock speed is directly related to pitch. Think about it like a record. If you increase the speed of the record, the pitch goes up.

      Fading between two crystals will not fade the pitch smoothly. At best it will just switch between the two without any transition. More likely the circuit will stop functioning as you try to fade between crystals and will only work at either extreme of the potentiometer adjustment (all the way up or down). Fading between crystals will only modify the amplitude of those two signals. One will decrease amplitude while the other increases. In the middle you will have a mix of both signals at mid amplitude.
      In order to change the pitch of the circuit you need to change the frequency of the clock not the amplitude. Changing amplitude will just make the circuit not “see” the clock and it will think there is no clock/ it will not work.
      Unfortunately the frequency of a crystal is inherent to its crystalline structure and can not be modified. It’s possible to replace the crystal with a high frequency oscillator which CAN be adjusted but that requires the creation and installation of a new circuit.

    • 31

      casper said:
      February 16th, 2012 at 9:00pm #

      #das data:
      sorry. i wouldn’t know where to start looking. I suspect the internet knows.

    • 32

      C.A. Duke said:
      July 8th, 2012 at 9:46pm #

      I have an SA-9 which has no out put jack. I know one can simply add to R/w speaker wire. I was wondering if anyone has tried soldiering in a jack that fits J2 on a MX-209 adding what ever needs to be at R1 & R2(possibly cut the MX-209 jumper wire) and see what effect it has since this port is supposed to be for a MX-210 with processor MSM6387-01 or MSM6387-01B. I was just wandering what the OKI M6387-03 would do. I haven’t found a 7-pin 1/8 jack to match yet.

    • 33

      Northstar Electronics said:
      July 10th, 2012 at 11:06am #

      I just stumbled onto your site while looking for the pin schematic for the 8053 amp, and I am pumped about it. I really like the layout of your site. The designs are really cool. I am really glad to find someone else that bends. I look at a lot for inspiration. I love to work with Casio products mostly, but overall just love to bend things. It makes me feel like a mad scientist. Again, great site. I look forward to learning some cool stuff in the coming weeks. Keep up the great work.


    • 34

      fossphur said:
      July 28th, 2012 at 1:04pm #

      Fantastic site, I am looking forward to adding buttons on my SA-8 for extra sounds. Cyberyogi from has a theory that with many additional diodes, the SA-8 could be played with 4 note polyphony. Has anyone tried this?

    • 35

      Rob said:
      September 27th, 2012 at 7:48pm #

      Do you know of any schematics for the casio CTK 550 and can these things be done on CTK with the same parts?

    • 36

      naf26 said:
      October 16th, 2012 at 2:00am #

      I have a Casio SA-7 and I know next to nothing about modification and bending so… can someone please tell me what is on the bottom of the buttons that touches the contacts on the board? (For that matter, what are the contacts made of?) I accidentally scraped some off of one of them during the process of putting in an output jack and the button no longer works. I’m hoping to restore that contact point. Thank you!

    • 37

      Simon said:
      October 22nd, 2012 at 11:26am #

      Help! While trying to do the crystal swap I accidentally snapped off one of the legs to the original crystal )-: Can anyone suggest what I can do or where I can get a replacement 22Mhz (with 3 legs)? Thanks.

    • 38

      casper said:
      October 23rd, 2012 at 7:29am #

      @Simon. The component you broke is actually called a resonator. This is basically a crystal with two capacitors from the out two legs that meet in the middle, just like the 6MHz replacement crystal shown in the schematic. I just did a quick search for 22MHz resonators and couldnt find anything. I think your best option may be to install a 22MHz crystal (here’s one from mouser)with two 22pf caps making a 3rd central point…. like in the schematic.

    • 39

      casper said:
      October 23rd, 2012 at 8:09am #

      @naf26. The contacts under the buttons are a kind of electrically conductive rubber. When this is pressed it touches two terminals of a conductive ink that have been printed on the board.
      This allows a small amount of current to flow across these terminals which tells the casio that a key has been pressed. If the ink has been removed or damaged you can fix it with a conductive ink pen. Unfortunately these pens are very expensive. I found one that is cheaper from Spark Fun. It looks like it should work but I cant vouch for its quality.

    • 40

      Simon said:
      October 24th, 2012 at 11:35am #

      Hi, Has anyone successfully been able to install the power crash on the SA-8? I’ve tried following the instructions above and using a 1K pot with a 1K resistor in parallel and I get nothing other than the untreated sound then if I turn the pot only a few millimetres the audio cuts out. Any clues as to what I’m doing wrong. Thanks.

    • 41

      Steven said:
      November 4th, 2012 at 7:56pm #

      I’m amazed that there’s such a big group of people hacking this thing. I found one in a bush several years ago and opened it up to clean up some exploded batteries today. Has anyone figured out what the unused solder pads next to the power jack are for? They look like they are labeled out put and are maybe the shape of a midi jack? Any takers?

    • 42

      nayto said:
      November 28th, 2012 at 2:34pm #


      I want to aks if some of you know were I can get a circuit bending tutorial about casio pt-1

      Many thanks.

    • 43

      casper said:
      December 16th, 2012 at 8:22pm #

      @Nayto. I haven’t played with one of those…sorry

    • 44

      Rolbista said:
      December 31st, 2012 at 10:13am #

      Hey, i’m in doubt about the feedback mod. The schematic of the SA-7 shows the audio input is at pin 6 of the AN8053 leaving pin 5 unused. The datasheet says the same. The picture on the other hand connects pin 5 to pin 5 on the OKI. Shouldn’t it be more like output pin from the AN to pin6 (output of the AN)? Also, I was thinking about making an FX loop on the way beetween pin 5 of the OKI and pin 6 of the AN, has anyone tried it? cheers, nice site

    • 45

      Rolbista said:
      December 31st, 2012 at 10:39am #

      “Shouldn’t it be more like output pin from the AN to pin6 (output of the AN)?” sorry, i mean input of the AN of course output->pot->input

    • 46

      tim said:
      November 10th, 2013 at 1:42am #

      Is it possible to hack one of these keyboards with an input (to run a mic, guitar, or other signals). What I really want to do is make an input that is compatible with the presets. I have tried this a while ago with an input, but was only able to hear unprocessed sounds through the speakers.

    Leave a Reply

    If you're not already logged in, there might be a question you need to answer before you post to prove you're human. It's there to help stop comment spam.