Making The Akai MPX8 Work!
Also the MPX8 Program Change Hack


by Sandy Sims Feb 18th 2014

  About a month ago, I decided to buy an Akai MPX8 Sample player to add to my "live-but-k.i.s.s" rig for local performances to get away from GM MIDI drums for a while. This is a cool little box that can access up to 500 samples, now in 16 bit stereo .wav format, and load up to 32 megs in any 8-pad "kit", from 99 presets. For $99 I thought I couldn't go wrong.
 Now before I go any further, I haven't made it my mission in life to rag on Akai's development team, nor steer anyone away from buying one of these as they *are* firmware updatable and I'm sure some fixes are on the table, and lets face it, what can you get for $99? A cheap cell phone, an evening out at the pub, a bus trip (one way) to Vancouver from, uh, just north of there. This was a really good thing for AKAI to dream up and I'm happy with it.

I know a lot of you are not, and that's one of the reasons I am posting this page so you can know there is a way out. all new products have their issues, most are fixed in the R&D stage, but, some sneak out untamed.

 Here's some of the problems / annoyances I've found with the MPX8:

1-Slow sample loading time. SD Card reads are faster than this, I've built stuff faster than this and I didn't even know what I was doing. Most drum samples are short so load in a flash, but a couple of long cymbals loading while my fans anxiously await my next tune, I anxiously think about how it'd be faster to load a real drum set onto the stage...
Now maybe there are faster SD Cards, mine are pretty old. (2 gigs)

2 -NO MIDI Program Change! I was completely amazed that there is no PC recognition at all! I hadn't even considered it wouldn't be there because it defies logic. Basically, just a MIDI input that duplicates the action of the little selector know you use to find a kit. Seems logical. But then in light of problem #1 above, perhaps they  just said to themselves, "It'll take too long to load, so what's the point..." or something like that. I have put in a request for that to be included in the next firmware update.

3 -Loop Issues, falling out of sync. This one doesn't bother me personally, because I'll never use the MPX8 this way, but some of you had great expectations. All I can say is "It's not a sequencer or a loop machine!"
It does raise some interesting experiment results:
I thought that these guys (gals) complaining were taking two samples, same tempo but maybe slightly different in size, and watching them fall out of sync. Idiots, I thought... So I took two exactly identical samples and loaded one into one drum pad, and the other into another, then started them both. Right away they are wobbling in and out of phase, then bye bye! After  a minute, the beats were 180 from each other already! Which is kinda not good.
As a programmer, I can't even imagine how this could be happening unless somewhere in the programming, hardware times are being used and... well I don't know really. Glad I'm not using it that way. Maybe they'll fix it.

Running Status MIDI Fix

Inline MIDI "conditioner" on a chip $27 CAD (see below)

If you want one, you'll need a paypal account for the moment

4 -MIDI Running Status Blindness. This problem is a biggie for a lot of people, including myself. I kept seeing posts on Akai's forum about skipping notes and no notes, or occasional notes. Funny, I thought, my MPX8 works fine with all of my MIDI sources. But then I realized I had been feeding it through my DIY drum sequencer first, even when the sequencer wasn't playing it.

When I wrote the program ( a few months back now) for my sequencer, I had issues with my Kawai Keyboards not playing all of the notes. It'd skip like a bugger. I monitored and sampled etc. and concluded that whatever the problem was, MIDI-ox and any of my PC DAW software was fixing it, as I've never had problems with the Kawai playing a soft-synth. So Out came the scope, and I basically counted notes I had played, then added them up on the scope. Some were missing! It appeared the Note On/Off commands weren't always there. So I searched around the 'net, not knowing what it was called, and found an article called
"The Dreaded MIDI Running Status". I learned that  it is / was used to squash more notes into a shorter time frame for heavily laden MIDI chains. A sort of compression that cuts off one third of the time by removing command bytes randomly in the stream. I quickly worked out a solution and had it up and running by the next day! With that in mind, I removed my sequencer and tryed feeding my Yamaha drums into the MPX8 directly. One hit, then nothing! OMG! What serendipity that I just happened to have built that a couple of months before!

So, over the past few days, at the bequest of a fellow MPX8 user, I have designed a MIDI fix for it. (Picture above, right) It's on a PIC chip and basically started working right away. I plug it inline, turn it on, and away it goes! My drums now trigger the MPX8, as does the Kawai Keyboards. Of course being a bit of an electronics engineer, I had to add some features, and after having found problem #5 (which isn't really Akai's fault, it'd be just pre-defined for any non-polyphonic-per-pad sample player (see below)

MIDI Fix Added Features:

Display: A  2-digit LED display that shows last note received in selectable hex or decimal (an LED for 100's indicator) format. MIDI i/o LED (also ticks to show on), MIDI R.S. LED.
Battery Saver: Auto display dimmer after 2 seconds, off after 10 seconds. If constant note stream (at least every 1.6 secs) then goes dark after 12 seconds, until notes stopped for
                       1.6  seconds. LED displays suck an amazing amount of juice so this was an absolute necessity.
C.A. or C.C. display option: Either display will work but Common Anode is brighter as the segments are sinked by the PIC. Common's are transistor driven (see schematic below)
Full-On Velocity Mode: Sometimes, especially with finger drums, it is desirable to have full velocity no matter how light you tap. This switch does that.
Double-Tap (Bounce) Processing: Turn this on to get rid of annoying "missing plays" due to a double hit. Non-Poly samplers don't like unintentional double hits. Nor do I. (See below)

5 -I thought I had everything under control until I noticed and discovered "Hey, sample players aren't like polyphonic GM MIDI synths at all! "
The big difference is, if for example, you hit a snare on a GM MIDI drum synth, but then hit it again. "Both" snares sound together. They are digitally mixed once the second one occurs. This is polyphony. With mono-phony (not sure what to call it) a second hit will cause the sample to start playing again, thus effectively eradicating the first's effort to play through...

Herein lies the issue of bad for drumming MIDI into the MPX8. Even if your MIDI sending v-drums or controller can talk well with the MPX8, this can still be a problem.

The screen capture from MIDI-Ox to the right shows what the issue is. The MPX8 will start to play note 0x32 at a velocity of 6A (106), but then 31 mS later, will start to play the same note again, but with a velocity of only 06.

It took a while for me to notice this, but after playing a while, major hits were just disappearing! It was a tricky load of programming, as other drums could be happening at the same time, (ug!) but I did get it.

Now I can Proudly say I have a true MIDI Fix! This will also work to fix running status on other things as well. I've been just banging on the drums ever since!

I am now selling just the PIC chip & Schematics for $27 CAD + postage ($5 CAD usually) for you DIY'ers out there, and at this time not sure about making boards...we'll see.

Contact me at freshnel@freshnelly.com if you want me to send you one. We are setting up with PayPal right now. (Feb18th 2014)



My ugly Board (which needs a box!)

6- I've discovered yet another MIDI situation that has been messing up the MPX8. I showed up when I had the MidiFix hooked to my Korg Micro-Korg. Every once in a while a note would be skipped, well quite often sometimes. I found that when the tempo/MIDI Clock output is disabled, eveyrthing works fine, but when on the skipping happens yet again!
  So away I went investigating. It seems the Korg actually sends the MIDI Clock exactly when it happens. It doesn't wait for a MIDI message to complete. This is a nasty little problem for AKAI to solve, I wonder if they'll figure it out? They likely won't ever be reading this haha!

 Sure enough the F8's are being inserted in the middle of running status messages, talk about sabotage! I simply moved the routine that picks up meta commands (0xF0-0xFF) to a location in the program before the routine that decodes running status .

 SO if you've been waiting / deciding on buying one of these, wait no longer. It's flawless!

 Anyway, here's the box I made because I'm being all environmental (using scrap wood) and too cheap to buy a proper box for it lol.



 I'm so happy I could share this project with you all, and I hope you've picked up some good ideas from it, or better yet buy the chip!

MPX8 Program Change Hack:

 After waiting for a couple of months, it's becoming apparent that the engineers at Akai Professional are not going to be coming out with a firmware update for the MPX8. This isn't a really big surprise to me as most of the users will be simply using the MPX8 as a sample pad/finger drum, plus they are releasing a newer product with recording ability.
So it looks extremely unlikely that I will ever get my program change firmware request, and I'll have to do a hack on the unit.

  Because Akai won't offer open source or any info at all, this hack is pretty simple & superficial, but it will do the trick...

The Circuit:
 The trusty old 4066 CMOS quad analog switch is still the best choice for hacking panel switches like remote controls (I've done), and various "unknown" circuits. The worry of voltage/timing is erased using this method. There should be one switch on every button for full panel access. The pads don't need 4066's on them as they can be selected using MIDI notes already right?

 I had a look inside the MPX8, and there's certainly enough room to put in the little board. If using an Arduino, don't have header pins attached as there is no room vertically. Also, there will need to be the 4066 "sheild" as a separate board so...
 I was looking to see if there was space enough to put some batteries in at that time I opened the MPX8, they'd have to be LiPo type, or AAA NiMH's. Also this unit is a pig on power (1/2 amp peaks), so an external USB battery pack may be better.

The Right Chip:
 Any PIC or Arduino with a UART to sniff the incoming MIDI will do, or a SW UART could be implemented I suppose. I want to use a "bigger" PIC so I can save the Program Change data, which will be recalled on start-up.

The Program:
 Basically, the program (sketch) must be able to hold down the VOL+/- buttons on start up to reset PC to i01, (don't worry about delay, these can be held down after .5 seconds from initial power up and it still resets) wait for 3 seconds for reset, release the buttons, then dial in the "Kit" by properly pulsing the encoder.
 This is where it is a little tricky. To mimic and encoder, there needs to be 2 pulses, one out of phase with the other.

 The waveform diagram to the right shows a basic idea of clock-wise vs. anti-clockwise pulses from the knob encoder. In a lot of hardware I've repaired in the past, the common line is constant, but in newer microcontroller equipment the common is strobed. This is partly because strobing reduces I/O pin count on buttons, but also because it can make debouncing easier to implement in software.

 The MPX8 will likely be strobed. This is not an issue using the 4066 switches to control the encoder lines, but to read when a user has modified the actual encoder knob, which will happen, requires that they be read (the 3 10k resistors) in a different way.
When one (or both) of the encoder levels is the same as the common, and the state of the level is that of the strobe, then the encoder switch is considered validly "on". It's important that the count is the same as the count the MPX8 will have, or everything will be out of phase after that!
 This isn't really crucial to the program change operation, but I like to have as many functions as the hack can provide, to make it more worthwhile doing.

Other MIDI Controllable Parameters:

 For my own personal use, maximizing the controllability of the following is a must!
1) Program Change: The primary reason for this hack, to be able to select Kits:i01-i09, e01-e99 via MIDI.
2) Tune: To be able to shift the sample frequency on the fly is bonus, and to use MIDI Pitch Wheel (9 steps) would be easy to implement. [ sel- x 8, sel+ x 3 ]
3) Reverb Control: Sometimes it's nice to have lots of reverb at the end of a bar on that last kick or scream. [ sel- x 8, sel+ x 4 ]
4) Pan Control: Because the encoder emulation must be at "human speed" this won't be an instant flip-flop pan, but can pan each note. [ sel- x 8, sel+ x7 ]
5) OFFset PAD Changes: If the other samples around the samples on the board are static (i.e. numbered so they are in a predictable order) then changing the PAD assignments
   during a song is entirely possible. This would need to be done with special MIDI Control Change knobs, or MIDI Bank Select. Also load time would need to be taken into
   account when creating the MIDI song / sequence. It *is* a possibility, although I probably won't be implementing it.
 *The data in [ ] is the sequence on the SEL+/- required to have the encoder pointing at that particular control. Remember the parameter must also be selected to a limit (left or right) first; so starting position is known as that will change with each kit loaded.

Receiving a Program Change :
  This is probably the most important sequence to the hack. When a Program Change is made by a human user, it will tend to send loads of program change data as the user selects through the 0-127 choices. Because of the way the MPX-8 handles the selection of Kits ( annoyingly short delay! ) the accidental loading of a Kit will be exactly the same in MIDI. The solution to this is to (a) increase the delay, or (b) initiate the PC using another such as any note, or CC.

 Myself, I prefer the delay method because it reduces hardware issues, but how long is enough? 2 seconds? That's my choice! Even in a sequencer, the correct "instrument" must be found when using automation, but it's basically an instrument selection that will be sent as soon as the song is loaded. In my huge project currently underway, Show-In-A-Box, the MPX8 will be sorta built in to the panel, so it's important my DIY sequencer *does* send the Program Change when the song is loaded. Some Samp's take so bloody long to laod!

 That is the last consideration, keeping track of the last loaded PC ( or the one loaded at start up) could reduce the load time by not loading it again! Keeping track of the PC will speed up "turning" the encoder by offset. So if on Kit 23, but now need to load 20, just go down 3.

 So there you have it. I'm pretty busy with my mega-project mentioned above so it'll be a while before this gets built, but hopefully it has given some of you makers out there some good ideas. And if anyone is considering buying the new MPX16, consider it carefully. It may be another MPX8 with more "stuff" to go wrong!  
I'll add on a program for the PIC, and maybe one for the Arduino if I get to that, here.  Cheers!

Design Notes:

 It's too bad the LCD display is so embedded, I had high hopes on being able to read the LCD data into the PIC to know what's on the screen. Instead it's just LCD voltages, pretty hard to tap off of without messing up the LCD display contrast etc.

This Update May 1st 2014


 Now summer's over I've begun to recommence with the el. projects, and this hack is a good spin-up to the more bumpy roads ahead!

  I've decided to continue with the PIC chip in this project, so if you're an Arduino head, this should be really easy for you to duplicate in script....well unless you work for Akai and  are the SW engineers that wrote the crap script for the MPX-8 in the first place in which case this is way over your head. Sorry!

 For the Show-In-A-Box integration, I can't use the giant side 1/4" jacks as they don't fit in the case I made! SO the headphones jack will be used. Using headphones with a unit that has no batteries seems stupid anyway. It's not portable hey.

Because headphone amps have lots of hiss, that circuit must be disconnected from the 1/8" headphones socket, the wires from the 1/4" jacks connected to there instead.

Notice L30 & 33 are cut in the picture. I also removed the 2 .001 uF caps on the headphone socket because the 1/4" jacks already have those and they'd only serve to dull off the high frequencies at higher impedances.

So there, that's done. Not really *the* hack, but a hack none-the-less.


  As per the diagram shown here (slightly revised from above), the buttons must be controlled by the PIC via CMOS 4066 switches. The encoder goes to ground so that's switch-able using a couple of Q's (3904's).

 Notice I've left the encoder sensing resistors in? Those are no longer for counting because with the strobe and variable debouncing between them and me, the PIC and MPX8 are bound to fall out of sync.
 Now they are to issue a warning (in the form of a flashing LED) that the encoder is jammed between clicks. They do that these new cheapo switches!

 I will be drilling a hole in the face of the MPX8 for it because I don't care anymore, but if you are doing this hack and don't want ugly hole in face, just stick it out the "security lock" hole... You'll never use it because nobody would ever steal your MPX8, at least not before the firmware update that would make it a much better toy!

 Anyway, back to the actual hack...
 In the diagram the commons for the buttons are for Volume buttons, and the Select buttons.

Now in the far right photo here, you can see where those must connect. I must admit, I had one *heck* of a time finding these. I never expected there to be a 4 transistor circuit to strobe 2 sets of buttons! WTF is my initial thought! I half expected a circuit like this on the pads but again WTF?? Maybe they ran out of I/O pins on that huge uP?

 I won't waste my time trying to figure it out any more than trying to figure out why dandelions are yellow not purple.

 The other sides of the buttons connect to the anodes of the 4 diodes hovering around the '573 octal latch from the pads. Coincidentally, the '573 is what I'm using to spread out the main control bus in the Show-In-A-Box project. They have very low power draw compared to the old '373/4 (and low $$)

  With the switches taken care of, the MIDI in needs to feed into the PIC to control them. The more I thought about it, the more it made sense to break the MIDI in connection to the MPX8's uP and feed it through the PIC instead. That way, the MIDI-Fix mentioned at the start of this page can be incorporated into this PIC as well!

 As a matter of design compatibility with any possible marketing of this board in the future (yep the MPX-16 is on the way lol!) and/or courtesy to any makers willing to take this on, the MIDI will be "fixed" so the MPX8 can understand it. For my use it's not necessary because the MIDI will be filtered and fixed long before it reaches this part of the chain in the box.

 Finally, the relay (because I'm too paranoid to use anything else) is to cut the power for a reset / startup condition on power up, and if there's an error or whatever, control can be re-gained.

Well that's it for now, I'll be doing a board up shortly, can't wait to get on this!

Updated September 1st 2014
 So I finally had some time to get the hack done!  It was a learning experience, and demonstrated further the sloppiness of Akai's programming on that damned encoder knob. It's scan rate must be pretty slow because all I could get out of it (reliably) was 6 switches per second!

 It went faster but errored after more than 10 positions. It's like the processor loses focus for a bit, then continues, missing 1 or 2 pulses from the encoder circuit. No wonder it's such a "crap shoot" to use by hand.

 Anyway, as can be seen in the diagram, a couple of changes had to be made. The main change is on RC2. This is an output to disconnect the encoder's ground, rendering it useless during MIDI control.
This "mostly" solves the problem of the encoder resting in the shorted position, but not entirely. If both are shorted, which happens at the peak of a click (where it normally can't rest in better encoders) the MIDI control is rendered useless.

 The LED indicates that either side of the encoder is shorted in bright yellow. The user can then tap it so it falls into one of it's tiny grooves, or wiggle it a bit. As long as it isn't roughed about, it generally stays in position.

 Switching out the encoder knob created another problem. When the MIDIFIX board receives the Program Change message (to change kits) the encoder is disabled. The problem is, sometimes when I'm working on a song in the sequencer, I need to select a different sample. I can't because the encoder no longer works!

 The solution is to turn the encoder after a reset, then control will be permanently on the encoder ...until a reset. On reset, I have made the MIDIFIX hold the Volume +/- together, then turn on the relay to power up the MPX-8. This does a reset and the Kit resets to "i01". The MIDIFIX then counts up 8 so the Program Change starting position is at "e01".

   ** NOTE: The PIC Chip is Now the PIC 16F887 !
 The most important aspect for the Program Change to work properly is to have all 99 kits on the SD Card. At this time, most of mine are empty, but having all 99 means using the built-in kits i01 - i08 is predictably at PC # 100 - 107.

 The second most important consideration is time to the kit (kit 1 to kit 99 takes 17 seconds!) and loading time after. So if kits are organized well, or there simply isn't a lot of active kits, then load times will be considerably less. This can be important during a performance.

Anyway, the select +/- buttons are controlled by MIDI Ch.10 Notes 121 & 120 respectively, and the encoder (for use with menu items other that kits) is Notes 122 for left, and 123 for right. I've made a bit of a list of do's and don't in the user manual , plus other features and methods.

 For anyone planning to try this hack, here's some photos of where to hook wires etc.

The photo to the right shows the trace to cut (Pin 7 of the 6N139 chip on MIDI sockets board) to put the MIDIFIX hack inline. Because the voltages are already inverted at this stage, no buffers/invertors are needed.

In this little photo, the white wire (on pin 7) is feeding the MPX-8 MIDI in to the PIC chip's USART. The black wire is feeding the PIC's USART TX to the MPX-8.

The 220 ohm pull-up resistor (to 3.3V)  is cut as the PIC chip will provide the 3.3V via a voltage divider (470 ohm & 1k resistors) with the new, fixed MIDI data.

  I almost forgot about the 3.3 volts thingy, as the PIC is normally 5 volts. In this case it's running at about 4.8 V because I had to isolate it with a LDO rectifier.

 On power-up, there is a massive surge on the included power supply, enough that the PIC chip resets. BTW the PIC chip is now a 16F887, NOT a 16F74. They're almost the same but I ran out of the others! Too much MIDI fixin' ;)

 The next modification is to the main 5V power input. The yellow wire in the photo to the right has the +5 volts BEFORE the switch. This way the MPX-8 can be turned off/on without the reset sequence, a sort of standby. The blue wire is from the other side of the relay.

 Now things get a bit more delicate. The Select and Volume +/- connections are all on the  4 diodes on the main board. Note they are all on the anode ( not-banded side) side.

 The red wire is the Select +, while the brown wire is the Select -.
 The Black wire is on the Volume +, and finally the White wire is on the Volume  -.

 The photo to the far right shows the Button commons. The red wire is the common for Volume buttons, and the brown wire is the common for the Select buttons.


The encoder hookups are Right is the upper pin, and Left is the Lower pin, if you are looking at the main board with the lettering going the right way.

 Finally, the encode ground is of course the center pin. This needs to be carefully cut so the main board must be removed. Be careful not to grease up the contact pads for the, er, pads! If you suspect you may have (finger sweat can be nasty to contacts) clean them lightly with alcohol.

 I used some really fine side cutters to snip it at the board (as shown). It's a pretty cheapo thing so be careful not to torque the case too much. The orange wire is going to the MIDIFIX PIC's RC2, port C,2.

 There's no need to worry about the 5 volts here as the pin is Tri-stated to high impedance when the encoder is disconnected.


 There it is! For the use I have planned, this improves the MPX-8 500%, and it can now do some pretty cool stuff with MIDI remote button control, like switching samples in a pad on-the-fly or pitch shifting. It's a bit slow and dodgy, but with some patience I have found it to be a real addition to the box.

 If you plan to build this, the .HEX is here, and eventually I'll list the .ASM file once I "clean" it up a bit (lol) If you don't do PIC, I can send you a chip if you send a kind email complimenting me on one of my songs (not my electronics skills because I know I'm good hahaha) and a bit of money for my paypal account (to cover chip and sending it) I can send you the chip.

 I haven't shown the board I did because it's really an embarrassing mess, but it did fit nicely between the 2 fat posts on the bottom of the case. That's under the pads area, no large caps or plugs there.

 Don't forget to read the user manual if you're considering this mod.

 One more thing before I sign off; using an Arduino in this project might be easier for some. I haven't written it for that, but the Pro-Mini would be a great choice. If you don't care about the crapping "running status" recognition in your application, the sketch coding would be pretty easy me thinks. Eventually I will be completely over to Atmel & Arduino, but for precision timing and high speed, PIC is still the way to go! ( Unless you want to use a Raspberry Pi, or Arm board lol! )

 Cheers all!

MPX-8 subject closed


Last Update September 21st 2014

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Thanks to Everyone at the Akai Forum for getting my interest in this!

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