Gearporn: Elektron Digitakt teardown


#1

Hi,

I recently got a digitakt (great machine!) and - being the person I am - I just couldn’t resist to take it apart and have a look inside. Here are some photos for those who are interested as well.

Flickr album here

Compared to the “Analog” series devices from Elektron, there are a couple of changes.

  • The new “encoders” are actually potentiometers (probably sin/cos). That’s very clever.
  • The “Analog”-series devices had a USB isolation to avoid having a ground loop when the device is connected to a computer and an audio interface. The USB isolation chip was removed. Instead, there is now an isolation between the analog side and the digital side of the circuits. The power rails and grounds for the analog and digital sides are entirely isolated. That way, ground loops are still prevented, but in addition digital noise is kept away from the analog circuity much better.
  • The magnetic NVRAM that was used in the “Analog”-series devices was removed (probably too expensive and too small - the largest available on the market is currently 16Mbit). Instead, they use a 1Gbit DDR2 SDRAM powered from a Supercap. So, effectively you get the “persistent” memory (no loss of data when power-cycling, even without saving your project) but it porbably won’t last 20 years like the magnetic NVRAM
  • The new switches are computer keyboard switches from Kailh - apparently that is a “Cherry MX” clone.
  • The type of OLED display is unfortunately not visible without desoldering it from the pcb.
  • They are still using a coldfire processor. To my understanding, that is pretty comparable to the higher STM32F7 devices (maybe a slightly faster) but interestingly the SRAM on those is only 64kB.

What else do you spot in there?


#2

Great, thank you! Never heard about sine cosine potentiometers before.


#3

I’ve never seen those in the catalogue of a pots manufacturer, but I would love to give those a try. It’s just a dual gang pot without the mechanical bits that block the rotation above 330° and below 30°; and the track of the second pot is rotated by 90°.


#4

Yes, i tried to find them, too. The Alpha ones in the digitakt can be found at shady chinese websites, but they seem rather pricy (can be as high as 15€ per piece!).
I guess they are great for human machine interfaces, where absolute precision is not important - but high resolution is. I have heard about those multiple times in the recent months, but never seen one for sale anywhere. I guess it’s still a niché type of thing - though I would think that this could change in the next years, because they seem to appear in more devices recently.


#5

The main board seems to be more than just 4 layers. There is almost nothing on the bottom and top layers so there are probably multiple power and signal layers inside the board. For a board of this size that is going to be quite a bit more expensive than a 4 layer board. I wonder if they had to do this for a specific reason.


#6

Maybe they wanted to keep people like you from reverse-engineering the PCB :slight_smile:


#7

Haha, what do they have to fear? The exiting stuff is in the software anyway. I’m not going to build “digitakt clones”.
Really, I’m only curious and like to understand how my gear works and what choices they made in the design process. Is there anything wrong about that?


#8

Yeah, was just teasing you! I actually find it really great that you have undertaken the task to tear the thing apart. Especially the thing about the encoders, which turn out not to be actual encoders at all was a great find!!!


#9

I was wondering when I’d see one of these summaries. Cool, indeed - now I just need my digitakt to ship out to me! I think it’ll suit my current situation well.


#10

RE: Processor on UI Board

Did you see the processor on the UI board? The Boot Menu Test reports a UI Firmware version number, so somewhere there is a second processor. From the photos of the back of the board it appears to sit behind the OLED. I wonder what are they using?

Really great to see these photos – Thank you for posting them SlowGrowth!


#11

Yes there was a processor behind the OLED but to see the part number you’d have to desolder the display…
To be honest, I don’t think there’s anything exciting about his second processor. It’s probably just doing IO glue stuff, like button scanning and debouncing, LED dimming, etc. I didn’t check but I’d assume the OLED itself is connected to the main processor.


#12

the dt could easily be twice as slim…


#13

Yes, but I gues they wanted it to sit nicely next to their other machines.


#14

Thanks SlowGraowth. Interest knows no bounds with me – which has both advantages and disadvantages…

I also discovered running the Boot Menu Test that the Main Volume Pot is not reported with the control tests. I think it is an analog only control – which accounts for all the connectors on the pot – it is ‘stereo’. So the second bus cable (the left one looking at the component side of the CPU board) has these signals going to the audio section on the CPU board.
(You’re right i am interested in this kind of stuff!)

I’ve been of several minds on the OLED’s control processor – definitely leaning toward your conclusion.

Rather than a slimmer Digitakt i’d put in a battery pack - Heaven. Then it’s the same depth and a cool little sampler and power free performer. (But the $650 price tag is nice too.)


#15

Also fun with the Boot Menu test is doing all the combinations with buttons 3 4 and 5 and seeing all the colors possible with the button LEDs.


#16

being slim is totally overrated.


#17

Also wondering what this is on the CPU board? I can’t find information on it. Thanks in advance.

SU1408_17409AE


#18

For this chip I don’t have a part number as well. Given the position on the board and the components around it, my best bet is that it’s the persistant memory for the +Drive. Probably some sort of flash memory. U5 right next to it is the SPI flash for the firmware (and maybe image resources for the display, factory patterns for the factory reset, etc). U3 is the DDR2 RAM. So there must be some persistant memory somewhere else and I think that can only be U8.

I wrote a lot of details in the image description.


#19

Strange i couldn’t even pick up on the manufacturer. A flash memory for the +Drive seems likely but i’d think the part number would be more findable. FPGA crossed my mind, but i see little purpose in the Digitakt, unlike the A4 and RYTM. It’s pretty big.


#20

No, an FPGA makes no sense here. There is not enough decoupling caps next to it. Also there is no programming interface or firmware memory chip. And the only useful function an FPGA could perfrom here is massive parallelled IO or some sort of interface glue logic. Both of which is not neccessary in the digitakt.

To be fair, U8 doesn’t come in the typical TSOP packages used in USB thumb drives etc. But if you check some datasheets (cypress for example) you will see that many flash storage chips are offered in BGA packages as well.
I guess the communication frequencies on flash chips aren’t very high (the memory itself is rather slow compared to RAM) so that’s why we don’t find any series damping resistors like those next to the RAM.