Mega MPS project

The Mega MPS - out in nature

I've been viewing Thomas Henry's designs closely and considering everything he designs. The main module that caught my eye was the Mega Percussion Synth. A demonstration on YouTube by NoizeToy2 got me really interested. But of course the trouble maker in me wanted to take it a little further. My first thought is that a single drum isn't as much fun as four, so I had to have at least four of these modules together. Then I thought we have to have some effects for this sort of setup and I had at the time also become aware of the DaisySeed by ElectroSmith which is a MCU based around an ARM Cortex M7 aimed at the synthesizer and effects enthusiast. Hence the Mega MPS was born.

Yeah I know that means Mega Mega Percussion Synth, maybe I should have gone from M2PS (squared) - actually that should be M4MPS really.

I decided to go with the MPS PCB design that already existed of which I purchased four of from synthCube. That was easy. The effects arrangement was a little more complex. I had to come up with a PCB design for this which was troublesome but more on that later. 

The MPS - Mega Percussion Synth - designed by Thomas Henry
The MPS is an analogue drum synthesizer with three sound generating sections aimed at creating different parts of a drum sound.

We have the Shell section which contains the controls - Pitch, Sweep, Decay, Level, CV Range. There's also a switch which controls the CV input source from an external source like a sequencer, from the output of the Impact or Noise modules. This creates some interesting distortions of the pitch.

The best person to explain the details of the signal flow is Thomas Henry himself. So over at Birth Of A Synth, is the author's explanation of the Mega Percussion Synth along with many of his other synthesizer related designs.

The Pitch control sets the frequency of the oscillator, the Sweep control applies a downward pitch shift based on the Decay value. The Decay also controls the decay of the amplifier. This section supplies one of the inputs for the Ring Modulator section. The Ring Modulator also has its own oscillator to complete the basics of its function. Here we find a Pitch control along with Depth and Balance. This allows you to create more metallic drum sounds that might be associated to cymbals or gongs.

The Noise section has the same controls as the Shell. Instead of a tone it is based around random noise. It contains a filter with a Low Pass and Band Pass mode. The filter has a resonance control to highlight and expand sections of frequencies.

The final section is the Impact, once again with similar controls - Pitch, Sweep, Decay and a Level control. The difference here is the Decay time is quite short, emulating the idea of a stick hitting a drum skin - the initial impact.

Each module accepts a Trigger input to trigger the module and there is a push button on the module to manually trigger it as well. I left the Sensitivity control in which I am presuming relates to using DIY drum pads. These can also be used to adjust for different input trigger voltages. The final control is the Hold switch which applies a gate signal allowing you to tune the pitches among other uses.

In addition to the standard panel I spent considerable amounts of time trying to get LEDs for each Section to happen. This took a few PCB designs and many destroyed LEDs but I managed to get it sort of working in the end. I have to say that it wasn't really worth the effort. 

As you can see from my unit I have four modules in a row with each modules' effect below. The next module along is the Mixer.

I wanted the MMPS to be a complete unit so it contains a mixer which takes all sources down to a balance stereo output. The four Level controls on each MPS module only affect the dry output to the mixer. Each MPS effects unit has its own input mixer where you choose what gets effected.

Each effects unit is based around the DaisySeed module. The printed circuit board design I made up has the DaisySeed is mounted along with a mixer so the various audio parts of the MPS can be mixed to the audio inputs of the DaisySeed. The board also processes the Trigger and Control Voltage going to the MPS which are utilised in various effects. 

The panel of the effects units are made up of a 16 characters x two lines LCD display along with a rotary encoder for selecting and changing parameters. There's also the input mixer to the effects which has level controls for Shell, Noise and Impact. There's also an extra level control which takes the mix from the MPS levels. This seems a little confusing but it made sense to have a single level control for the effects if all you wanted to do was mix all parts of the MPS instead of individual parts. The mix from the Effects unit goes to the Main Mixer of the MMPS.

The DaisySeed seemed like a dream unit as it had all the functions written for most standard types of effects and it was as simple as linking the audio through each different effects but I did have some issues with digital noise within this module which haven't been fully removed but I have managed to reduce it.

Lots of fun was had choosing the various effects for the module. The DaisySeed comes with a whole bunch of functions for creating effects and synthesizer modules as well. At this stage I have a Moog Filter as the first effect, this is followed by an Overdrive, then we go through a Stereo Panner and onto the main event which is a Stereo Delay with a crazy feedback loop. The Feedback loop of the Delay contains a multi-band filter and pitch shifter along with cross mixing. The delay can be controlled by the Trigger input in that it can be set to pick off two triggers and create a delay time based on this and the chosen divisor. The control voltage is available to control effects but I have not used it at this stage. I've not had enough use with the Mega MPS to decide on the final effects to work well with it.

As you can see from the panel design, we go past the mixer which shows the level, pan and effects controls for each module, we have the Module Inputs. This is where we input Trigger and Control Voltage connections. Below this panel is the Module Direct Outputs which outputs each modules mix based on the module's internal mixer.

The Case
This continues with my attempts to make my cases on my CNC router. The challenge for me on this one was not to use any nails or screws and I managed this. I managed this with lots of difficulty and error with the Therematron case. But with some research I managed to find a method that was less taxing.

Sometime back I decided to "invest" in a biscuit joiner power tool. This tool cuts rounded slots into wood where you place glue and a wooden biscuit that is matched to another piece of wood with the same type of slot. There are many critics of the biscuit approach to joining wood but for me the ability to move things around before I need to finally clamp the work is a great advantage.

Several pieces of the case had to be done in multiple positions on the CNC router as mine is quite small, but this turned out to be quite easy.

As with most of my projects, the power supply for the unit is a separate unit at the end of a couple of microphone type aviation plugs. 

And finally, here's a video of my running a Beat Step Pro into the Mega MPS and demonstrating some of its capabilities - Mega MPS Demo