Friday, 28 May 2021

Passive Modules

Finished guys
It looks like it has been a year since I built my last DIY module.
Time for some passive modules I guess.

I ordered two 2-hp blank.  I needed another multiple to fill the rack and I decided to experiment with some passive functions.

A passive multiple is very basic.  You simple connect the tip and ground of each jack.  In practice the ground connection is established via the aluminium panel.  No need to use wire.

The main difficulty here is at 2-hp, or a bit more than 1 cm width, you do not have a lot of margin to drill your holes.  You do not want the body of the jack to go over the edge.
Not perfect but good enough.
I used mostly very cheap jacks I got a long time ago, except for the one with the switch as the switch on the cheaper ones is really terrible.

Behind the scene

Bob at work with the panel
I also experimented with some minimal panel marking by using my Dremel to carve some traces and fill them with a permanent marker.  This should not age very well. Time will tell.

The second module is the combination of a passive OR and a half-wave rectifier, ideal to combine gates and manipulate control voltages or distord audio.  You’ll find  the layout for both of them at the end of the article.  I got the schematics from unrecordings! blog

In the rack

In the following piece, the Korg SQ-1 produces two tracks of gates and CV for the kick and hi-hat.
I used the multiple to distribute the gates everywhere in the synth and I used the OR function to build a third melodic track from the first one and the output of the Turing Machine,  clocked by the second track.  I know it sounds complicated.  Patch schematics is at the end of the article.
The half-wave rectifier produces some overtones to spice up the sounds.
The variations in the piece is me playing with the sequencer.

Connection layout

Patch of the day

Sunday, 11 April 2021

Emilie's Last Stand

So I got Beads.

Not the decorative string of pearls, the Eurorack Module from Mutable Instruments.

To be more specific, Beads is the last design from Emilie Gillet, founder of Mutable Instruments.

Just unboxed

Powered by ARM

Beads is a revisit of Clouds, maybe the most successful Mutable module.

I always thought I'd get one one day.   Alas Emilie discontinued it more than 3 years ago.  Beads development took more time than expected, which created frustration and anticipation among Eurorack aficionados.

Beads, as Clouds, is dubbed a "granular texture synthesizer".
Basically, Beads samples its input continuously and creates tiny bits of sound or grains.
Up to 30 grains can be created and processed.  


From the manual :
One way of picturing how Beads operates is to imagine a tape loop, on which incoming audio is continuously recorded.

Every time you request a grain to be played (in reaction to a trigger, a button press, periodically, or randomly), a new replay head positions itself along the tape.

If this replay head doesn’t move, the audio will be played back at the original pitch and speed, but if it moves closer to, or further away from the record head, the signal will be replayed at a different speed and pitch. This replay head has its own amplitude envelope, and it will leave the tape once the envelope has reached a null amplitude.

Now imagine up to 30 replay heads flying along the tape. Imagine you can stop the incoming audio from being record- ed on the tape so that all these little replay heads can freely move along and gather sounds. And there’s a reverb…

Bob unscrews previous module

The module manipulates the density, size and shape of grains, as well as the time and pitch of the replay.  In certain modes, this is a reverb, or a delay, or both.
Grain density can go up to audio rate, creating new sounds in the process.

I thought it would make a great addition on my most ambient patches.  And with 14HP, it perfectly replaces my home made phaser effect module.

In place

Here is a small example of a drum loop made with the synth going through Beads in the Sunny Tape audio quality.
First you hear the sound unaltered.  Then Beads comes in progressively.   Grain seed is in sync with the drum sequencer.  You first notice the reverb as grain density start from very low. Then the grain density increases.  With small grains and low density, you hear the individual grains.  
I play a little bit with some settings and go up to 100% wet on Beads.
Finally, I select the random mode for grain seeding and I slowly bring back the unaltered sound in the mix.

Here is the full patch :

Friday, 17 July 2020

Three years

Three years ago, when I started this blog, I wanted to share my experience of making a modular synthesizer. First in English only, the blog contained electrical schematics and technical explanations. A few months later, I decided to create a French version to share this journey in the world of modular synthesizers with more people around me. The French version contains less schematics and more sonic illustrations. The articles are pretty much the same, but the two blogs are not 100% identical.

This is the 36th article on this blog. I kept on with my goal to publish one article per month on average. Some months were more prolific than others though.
The blog has now more than 19000 views and 10 comments. 21% of the audience comes from the USA.  The most popular article is the one on the Output module with 1200 views.

Since August 2018, Bob, a little Lego figure, accompanies me on every article about building something.  Initially relegated to cleaning tasks, Bob was able to show some skills in drilling or module tuning.  His small size makes him a valuable partner for delicate work.

There were so many evolutions between the first family photo in September 2017 where my first modules are finally assembled in a 3U Eurorack synthesizer row beginning and now with almost two finished rows of 84HP.  The synth includes, from top to bottom from left to right, One ADSR envelope generator, one CV quantizer, two oscillators, two filters, four VCA, one phaser effect, one output module, one sample & hold with noise generator, one slew limiter, two attenuators, a mixer, a voltage reference, a double multiple, one chaotic modulation generator, a signal multiplier with CV offset, a double modulation generator, one random generator and a resonator.

First family photograph, September 2017 :

And nearly 3 years after....

Some of the big steps are detailed here below :

- my first module (August 2017 - built on November 2016) : you have to start somewhere

- the case (February 2018) : modules have a home now

- first kits (May 2018) : I now have nice modulation sources

- repairing my VCO (July 2018) : I finally have a tuned sound source

- Doepfer DIY (September 2018) : comes with my first filter

- Replacing the Doepfer DIY with separated elements (early 2020) : new ADSR, new VCO, new filter.

I learned a lot on this journey into the world of do-it-yourself synthesizers.
First of all, I improved my brazing technique.  I can now make denser builds than before.
I've learned how to design module panels.  I also tested and approved new suppliers, such as Thonk.
But more importantly I learned how to use the synthesizer, how to use it to create generative music, how to create different types of sounds.

I used the synthesizer to make 21 tracks.  Mostly as illustrations of the function of a module for the blog, but not only :
- 11 sound examples of the module at hand;
- 7 sound illustrations of the state of the synthesizer;
- 2 participations to the monthly KVR Music Cafe;
- 1 participation to Audiofanzine Inspired Composition (Compos Inspirées).

And here is the track of the day :

All sound from the modular synthesizer.  Too many tracks to detail them all. 
Most tracks were performed in a very traditional way for me : first writing and recording a MIDI track, then programming the synth sound and recording the audio using the Korg SQ-1 sequencer as a MIDI to CV converter.  Exceptions : drums were made using the SQ-1 as the sequencer and percussion were generated by the Turing Machine.
DAW : Reaper

Saturday, 30 May 2020

Sloth Chaos

Ready to be mounted in synth
In a chaotic system, tiny variations of the initial conditions lead to apparently random states of disorder.  A chaotic circuit in a modular synthesizer is the promise of slowly changing, never repeating ambient soundscapes.

This module produces two different, very slow, chaotic CV signals. It is my implementation of the Non Linear Circuits Sloth Chaos.  I chose the regular version with 1 cycle every 15-20 seconds.  Depending on component values, other versions include Apathy (about 1 minute), Super sloth (15-20 minutes) and Stasis (about 1.5 hour !).

I needed to accommodate the values to match what I have on my drawers.  I tested on a breadboard to see if little changes on some components values would make a difference.  It turned out that yes, it does make a big difference.  It looks like there is a pretty good balance between the feedback and the small signal, going to the integrator for the big signal.  The torpor potentiometer plays with that balance.  But go with 20% more or 20% less resistance on that path and you end up with either two synchronous, though out of phase and saturated signals, or two chaotic but very small signals.
The butterfly pattern on the oscilloscope is called a strange attractor (or Lorentz attractor) and is the plot of the two signals out of the circuit, each one on a different axis.  When the signals are roughly in synch they form an ellipsis.  Two wells of pseudo equilibrium are visible.  The signals spend a bit of time there before drifting apart.  None of this is predictable and highly depend on initial conditions.  Hence the chaotic nature of the circuit.

I did not have 91k resistors, 82k + 10k  would do the trick.  100k was too high, 82k too low.  Same with the 4.7M, replaced with 2x 2.2M.

I also made a small change in the original schematics.  I wanted to have the LED be less than a negative/positive indicator and follow the signal a bit more.  So I chose the output of the buffer after the small signal output instead of the output of the following opamp.

Adapted schematcis

Almost there

The main board is really cramped.  Those 1uF capacitors were bigger than expected.   I really had to be very cautious on some connections.  It's a little bit of a mess at times, but I'm quite happy with the result.

The two boards before assembly
Victory !

After some minor corrections to both the layout and the wiring of the boards, I finally got the familiar chaos attractor pattern on the oscilloscope. 

Torpor potentiometer does not have a lot of effect.  Tough it seems to me that the signals are spending more time around a stable state (i.e well) when the pot is maxed out.

Marking holes before drilling
Panel design is inspired by Clarke Robinson's panel with the small butterfly reminding of the popular view that even the minuscule disturbance of the air due to a butterfly flapping its wings in China can cause a hurricane in Texas

Bob cutting the hole for the potentiometer

And now a bit of sound.
We have here two saw waves originally in tune.  One of them detuned by Sloth small signal.
The filter cutt-off frequency is modulated by Sloth big signal.
Low Pass output goes to the phaser.
Band Pass output goes to Rings to Rings, modified by Sloth and output from sample & hold.

Rythmic gate from TAL Filter 2 and reverb from Voxengo OldSkollVerb in Reaper.

No VCA was harmed during the making of this piece.

This seems to put a close to the bottom row of the synth suitcase.
Synth suitcase bottom row

Sunday, 3 May 2020

Slew Limiter and Passive Attenuator

Next in line is a simple slew limiter associated to a passive attenuator.

Nothing fancy.  No CV control.  No choice of slope.

Finished module
When I removed my DIY-101 module, I lost the portamento on the oscillator.  Mind you, I seldom used it, because the VCO was not good enough. 
Nevertheless, it is an effect I fancy on an analog oscillator.

Bob drills the panel.
The slew limiter circuit is inspired by Yves Usson own Dual Gated Slew and the simple schematics from Synovatron.  Components value were constrained by what I had on my drawers at the time.

The attenuator is a simple passive one.

Layout and schematics

I changed the way I wired the panel.  In fact, I don't wire it anymore : pots and jacks are soldered on their own PCB, with the main board attached via spacers.  I'm not sure it spares connection wire but it is cleaner on the panel side : no more screw.  On the other hand, I have to be very accurate with my designs and my drilling.  I did three paper prototypes before finding the correct positioning of things.

Thonk proved a good resource to find the appropriate parts.


Finally, here is a small sonic example.  The effect of the slew limiter on the pitch CV of the oscillators can be heard after 16 seconds.

Sunday, 29 March 2020

Inside the machine

Here is the current state of my suitcase modular synthesizer.

With only 2 rows of 84 HP (plus a couple of modules on the side), it does not look very impressive.  Anyway, with two oscillators, two filters, four VCA and the bottom row full of CV modulators, it can still be put into good use.

Here is my first take on what is called a Krell patch.  You'll find the patch detail below.

It is a single mono track, directly recorded into Reaper with some delay and reverb to give a bit more volume.  It's an assembly of two parts of a longer session.

It is self generated.  There is no sequencer, just a bit of manual parameter change here and there.

The sound is reminiscent of the soundtrack from Forbidden Planet.  The Krell are the extinct race of advanced beings of the planet Altair IV.  Hence the name of that style of auto-generated music.

There a two voices.

First a drone voice : saw wave from Mammouth VCO into Ripples, modulated by Rampage envelope and the output of the sample and hold.
Second : square, triangle and sine from Doepfer VCO mixed into Erica Synth VCF; Band Pass output goes the VCA, then Rings; resonance and cut-off frequency of the filter are modulated by a mix of the two Rampage envelope.
Both oscillators receive pitch CV from 2hp tune fed with the output of the Turing Machine.

The two envelope of Rampage are in cycling (i.e. LFO) mode.  First is relatively fast, the second reasonably slow.  The End of Cycle of the first gives the pulse of the system and the clock to the Turing Machine.
The apparent random behavior is provided by the modulation of the Rampage parameters : fall CV of first envelope is the second envelope and rise CV of the second envelope is the noise output of the Turing Machine.

Here is my first approach to document that specific patch.

Saturday, 28 March 2020

New filter

Now that I got rid of my DIY-101 based on Doepfer DIY, I'm back to a one filter configuration.   And that filter, Ripples, does not have a high pass output.  I was in need of a new multimode voltage controlled filter and I chose Erica Synth Multimode VCF kit.

Multimode VCF

This is another straightforward kit.  It is rather dense, despite being comprised of two boards.  The kit comes with three bags of parts : one for each board then there is the traditional potentiometers and jacks.

The kit
Sorting parts
Bob cuts resistors legs

The documentation (online, once again) is heavily illustrated and pretty complete with schematics and placement files.  No step by step instructions though.   Just photos of boards at various steps.

Boards are dense but perfectly labeled.  I noticed a single mistake : boards label called for 51k resistors and I received 56k (or was it the other way around ?).  I reckon a 10% difference is no problem.

This went like a breeze.

Main board, chilling on the bench

Odd capacitor placement
One oddity though is the fact that the boards are so heavily packed, they felt the need to solder the electrolytic capacitors upside down on the control board.  Two of which have to be bended parallel to the PCB because the main board will be above them. I put some insulation tape between the board and the capacitors despite the fact there is no indication to do so.  Better safe than sorry.

These capacitors have to be soldered the last according to the manual.  But I would rather put them after the standard parts and before the jacks and pots : once they are put in place, it is quite full.

Anyway, here it is, mounted in the synth.  That first row is now nearly set.

One thing I found a bit odd with this module is the placement of the potentiometer.  I would have put the c-off cv and reso cv close to the corresponding jacks, same with the audio level.  So I would have preferred an inversion of the two rows of potentiometer.  I would have found it more logical.

VCF in place
I do not have any 2 HP blank.  A clear oversight from my side.  I now have that small 1cm gap between the Mammouth VCO and the Erica Synth VCF.  It is supposed to be filled later with a 2 HP multiple.

So, here is a small piece of sound from the synth as it is.

Two tracks recorded live from the modular. Each track is sequenced by one channel of the Korg SQ-1.

DAW : Reaper

Usual effects : TAL Dub II, NI Supercharger, Voxengo OldSkoolVerb, Thomas Mundt LoudMax.

Bass voice : saw and square from Doepfer VCO to Erica Synth VCF Low Pass directly to VCA. Modulated by envelope from Befaco Rampage. Very standard.

Drum voice : mix of two parts.

1. Ripples pinged by Rampage, modulated by second envelope of Rampage and sequencer.

2. Rings, same trigger, same sequence.