MATRIXSYNTH: Percussa Super Signal Processor Eurorack Module Update

Wednesday, January 24, 2018

Percussa Super Signal Processor Eurorack Module Update

via the Percussa SSP kickstarter:

"Front panel finishes, switch caps colours, menu system updates, demo case and more

Hi all!

It’s time for another update! This week the NAMM show is happening in Anaheim, CA, one of the main tradeshows for musical instruments and music technology. We are not exhibiting or going as we decided to focus on the development of the SSP. A lot has happend over the past 10 days, below is a summary of what’s new including lots of nice photos :-)

1) Ordering more parts for the upcoming production

We already bought most components with long lead times for the SSP right when the kickstarter finished (such as the CPU modules), and now we continue buying the rest of the parts, such as switches, switch caps, ADCs and DACs, etc. Our commodity components will be bought further down the line as we get closer to production. We already got our programmable logic ICs which we received last week from our parts supplier, which is one of the few lead time sensitive parts specific to our design that we wanted to have early on so we don’t have to delay the assembly and shipping later on. So planning wise everything looks good, we got our PCBs, front panels and most of our lead time sensitive components. We’ll continue buying over the coming weeks and keep you updated about the production of the SSP.

2) Further experiments with front panel customizations

Our initial idea for front panel customization was to do laser engraving, but we wanted to see what it would look like if we machined our logo (and potentially any customizations) into the front panel before anodization instead of doing laser engraving. Laser engraving looks like gray text on a black background while with machining you can have more subtle customizations. I did the machining for the prototype below on our own CNC router. We’ll make a decision about what process to use over the coming weeks.

Besides that we are thinking about cosmetic hardware features ways to make navigation as easy as possible in our software user interface, such as different colours of switch caps. Although originally we planned to use only black switch caps, we might group certain buttons together using a colour, for example red for the cursor keys and grey for the menu keys, while the function soft keys would remain black. Below you can see an example grouping. This might still change as we continue working on the software and see the need to group certain buttons together.

Finally, we've chosen knurled nuts to go onto the jacks of the module. Nuts shouldn't be necessary for the SSP, because the front panel is attached to the PCB using 5 support studs, but just to make sure, we'll be installing knurled nuts anyway. We also ordered a manual tool to do this and will look into getting an electric tool to speed up assembly.

3) Updating the menu system of our exisiting code base for our synthesis software so it runs on the SSP

While we finish the hardware bringup of the SSP, myself and Celine have been updating our code base to use the specific button and encoder layout of the SSP (the same code base is used on the Percussa Engine / Remote). This involves going through all the different menus and checking the button assignments, updating button and encoder handling code.

Our code base is hundreds of thousands of lines of code, so it takes a while to go through everything we need to change for the SSP. Besides that we are also adding and debugging features which are new to the code base and which we showed in the graphical mockups for the SSP such as the 2D module grid editor. Below you can see a “debug” overlay of our application which allows us to visualize internal variables and states in the application to see what’s going on. We’ve used this overlay to find some really subtle bugs in our network editor.

Some editor screens such as those for the wavetable oscillator and envelope generator have slightly different layouts with the new mockups than they had when we did demos using the Percussa Engine, so we’re updating the code there to match the mockups. I’m guessing we’ll need another 1-2 weeks before we’re done with the meny system and GUI updates, and before we have an Alpha version of the software (basically the exact same software as we used for demoing on the Percussa Engine, but fully functional on the SSP according to our mockups and SSP-specific menu system / button / encoder assignments).

4) Building a demo eurorack case for the SSP and testing the mechanical fit and verifying there are no power issues

Up to now I was testing the SSP using a seperate meanwell power supply. I’ve now bought a eurorack case (intellijel 84HP 7U performance case) and a bunch of modules to test the mechanical fit of the SSP and run it inside a case off a typical eurorack power supply. I’m pleased to say it fits well and there are no mechanical issues. I will machine elongated holes at least on one of the sides of the SSP front panel just to be sure. I’ll be using the modules I bought for compatibility testing along with my Arturia Keystep controller (which has CV / gate out). I still haven’t finalized the case and might still swap a few modules in or out. Check out some photos below of the case. I’m stil waiting for the Make Noise, Erica Synth and Music Thing Modular modules to arrive.

5) Testing and debugging the audio drivers for the SSP at different sample rates using linux utilities and our own software

As I explained in previous updates our SSP’s main CPU uses programmable logic to connect to the 16 audio inputs and 8 outputs which support up to 192kHz / 32 bit, and which are DC coupled and support eurorack compatible voltages (-5V … +5V). We’re still testing the inputs and outputs, at multiple sample rates. I’ve updated our application code to use the 16 inputs and 8 outputs, since it previously assumed less input and output channels (as is the case on the Percussa Engine). It’s all working well, and I’ve already got the 16 inputs and 8 outputs working on our application, but are still chasing a few subtle bugs in our programmable logic and driver code. We’ll continue testing and bugfixing and optimizing our linux kernel configuration as necessary over the next week. Below you can see some photos of my test setup where I’m checking the voltage swing on the outputs using my oscilloscope (a little over 10Vpp as you can see on the scope).

That's it for now. I hope you enjoyed this update, while we continue coding. Until next week!

Bert & Celine

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