Sunday, 29 September 2019


My latest acquisition from Mutable Instruments is the Ripples filter.

Ripples unboxed.
With only one filter in my rack, it was not easy to have more than one interesting voice at a time. 
So I thought I needed another one to extend the capabilities of the synth.

Bob pushes modules around to make some room in the rack
For me Ripples has three main advantages :
  • I like the designs from Mutable Instruments;
  • it's a 4-pole 24 dB/oct filter and complements the 12dB/oct from the Doepfer DIY;
  •  it includes a VCA and it's a precious space saver in a small system like mine.

In the rack

There are 3 CV inputs : one for resonance and two for the frequency.
There are 3 filter outputs : 2-pole band-pass, 2-pole low-pass, and 4-pole low-pass.
The 4-pole low pass through the VCA is the latest output.

Getting Ripples and the Turing Machine change my initial plans a bit.
But that's the principle of having a modular synthesizer I guess.

It begins to take shape…

In the track below, hihat is white noise from the Random Module into the high-pass Doepfer fllter then on the VCA driven by the channel A of Rampage.
Kick and other percussions are from the same noise source into Ripples and on the VCA driven by channel B of Rampage.
Melodic lines are sine from Doepfer VCO into VCA driven by the envelope from Doepfer DIY, then passed through the phaser.
Sequencing wise, the first channel of the Korg SQ-1 triggers the hihats and serve as clock source for the Turing Machine.  CV out modifies the length of the rampage envelope to get longer hihats at times.
The second channel triggers kicks and other percussions.  Different percussions are obtained by modulating the frequency of Ripples.
Finally, driven by the clock from the first SQ-1 channel, Turing Machine provides gate and random notes CV (tuned by 2hp Tune) for the melodic lines.

DAW: Reaper
This is a single track from the synth plus a bit of chorus, delay and reverb.

Sunday, 8 September 2019

Turing Machine

The latest kit I built is the Music Thing Modular Turing Machine mkII

Turing Machine chilling on desk
Even if the boards are quite crowded, this is an easy build, thanks to the excellent documentation that comes with it.  The online build manual from Thonk is very well organized (smallest parts to tallest) and massively illustrated.  The fact that both value and component references are printed on the board is a real bonus.

Resistors first
Nothing special to tell, apart from the fact I soldered a 51k resistor instead of a 5.1k.  I simply misread and didn't double check.  Nothing serious : desoldering the wrong one, soldering the good one.

I used the documented trick to put some masking tape to align the diodes to the facade.  My diodes were well aligned but this left some greasy mark on the beautiful  facade.
Make sure your masking tape is not too old and will not leave marks by testing on the back side !

Finished boards

What is a Turing Machine ?

Bob calibrates the module
It is a pseudo random looping sequencer made from logic chips.  It is based around a shift register circuit.
You cannot program it or save sequences.  It produces clocked randomly changing control voltages.
The big knob controls how much randomness you put into it.  At noon, you're supposed to have a fully random sequence.  The more you go left or right, the more the loop is locked and stable, according to the length control.

Being fully made from logic chips with no software, the module can be clocked at audio rates to creates random wavetables as well.

Ready to assemble !

A word about the name by the designer, Tom Whitwell : "The Turing Machine is not a real Turing Machine the way Alan Turing explained it. The name is vaguely relevant because the module uses a loop of data being changed, but computer scientists find it very annoying. "

In the rack
Finally, here is a sonic example of a piece composed of 4 random tracks where the pulse output of the Turing Machine triggers an envelope and the output is passed through a quantizer to produce exact notes.  I added some pads and drums from software synths and voilà :

Sunday, 25 August 2019

MIDI Thru Box

Finally, I closed the lid on the MIDI Thru Box I was working on for a loooong time.
Not that it was particularly difficult.  I really was a slacker on this project.

Testing the finished product

Validation on the breadboard.

Printed Board Assembly
I took the basic schematic from the very good Papareil Synth Lab MIDI page (sorry for the french).  You'll find schematics and layout at the end of this article.

I chose to slightly modify the original to have 5 outputs out of the 6 inverting Schmitt trigger of the 74HC14.  The input LED indicator is driven by a transistor.
As I wanted to power the circuit with a standard pedal power supply (9V - center negative), the circuit has its own 5V voltage regulation.

Bob cleans the mess during drilling

Circuit assembly went like a breeze.
Drilling the box needed a bit of attention with the small M3 holes next to the big ones for MIDI jacks.

Drill box

As I assembled the whole, I noticed I didn't pay enough attention of the thickness of those MIDI jacks.  The electronic circuit could barely enter.  The last connections were not easily soldered.

I didn't see how I could test it without putting everything in its final place.  I really was worried about a possible debugging session.

My poor ESI MIDI interface gave me the creeps as I was testing.
But finally, all went fine and I found no mistake to correct.

Testing with a couple of Korg Volcas

As promised, the full schematics :

Tuesday, 19 February 2019

Tune by 2hp

Tune, unboxed
I needed a 2 HP module to fill the case.
And I wanted a pitch quantizer to experiment with randomly generated melodies.
So I ended up with Tune from 2hp.

2hp is a company that makes module 1 cm wide (or 2 HP).  They have quite an impressive range.
I reckon that a synth exclusively made of 2 HP modules would be a nightmare to operate as the controls are small and would be too close to one another. But I guess it's OK to have one or two in your rack.

What does it do ?
According to 2hp : "Tune is a multi-scale pitch quantizer. It features 11 scales ranging from chromatic to octatonic with everything in between. In addition, the bias control allows the user to transpose the melody to a different octave or starting note."

Bob screws it in place

Pitch Control Voltage (CV) is, in Eurorack standard, one octave per volt.  Add one volt in control voltage and double the frequency of the note.    There is no reference to a specific note (like 0V = C).  The CV gives you an interval : about 83 mV per semi-tone.
Reference or starting note is given when adjusting the tune knob of the VCO when no CV is entered.

So you enter a voltage in Tune and Tune gives you back the closest multiple of 83 mV aligned with the scale of your choosing.  Ain't that cool ?

In action

A touch of sound to finish.

Rampage is giving the tempo of the piece.  The end of cycle signal of each section is used as trigger for the other one : when one envelope ends, the other is triggered to start.  The rise time of the second envelope is controlled by the random generator, hence the variations in time and in the sound.
This patch uses the three available envelopes : two from the rampage and one from the DIY-101.  The two synth sounds are modulated by these envelopes thanks to Veils.
Rings generates the percussive sound in sync with the start of the first rampage envelope.  Variations of the structure parameter are given by the random generator.
All sound generators uses pitch CV coming from Tune.  The input of Tune also comes from the random generator.
Finally, I added a bit of chorus as well as tons of delay and reverb in the final mix.

Sunday, 10 February 2019

You can never have enough VCAs !

According to the popular motto : "You can never have enough VCAs !" 
So I bought four of them in a single module from Mutable Instruments.

Veils, unboxed
VCAs are Voltage Controlled Amplifiers and are essentials to shape the amplitude of sounds and other signals.

Not much to add here other than this excerpt from the MI website :
"Veils provides four VCAs with an adjustable response curve.
Veils’ outputs are daisy-chained, allowing adjacent groups of 2, 3, or all 4 channels to be mixed together."

As its becoming crowded inside the synth case, Bob went down and gave me a hand to plug the module on the bus board.

More to come....

Veils, installed