My Own Input Module

To close the 4HP gap at the bottom left of my synth case, I added a last input module. It will allow me to enter some external signals and bring them to the voltage level of the modular synth.  Moreover, it has its own piezo microphone.

It is modelled along the lines of Music Thing Modular Mikrophonie and Mutable Instruments Ears.

Input module

One input, an amplifier and an envelope follower for good measure.

The design is based on the original schematic for Ears from Emilie Gillet.  I kept the input gain stage. Due to space constraints, I had to simplify the envelope follower. I’m still doing pass through breadboard here, so this is not dense enough to have the same features as a full fledged Ears (or Microphonie Mk2 for that matters).

It took me a while to figure out the details. I had one operational amplifier available. The other being used by the gain stage. I was going for a short attack but not so short release with the right amount of filtering. Still not perfect : the shape is good enough but I fear that without the proper buffer at the end, I may not be able to drive any type of circuit.

 

 

Breadboarding the circuit : envelope follower output on top.

Piezo attached, other for scale

As I wanted to have some bumps to be able to scratch the surface above the piezo, I went with a different technique for the front panel.  It is the technique I used for the previous 2HP modules I made : dremel some lines and blacken them.
 

Bob helps with the panel

 

 

 

 

 

 

Mistakes I made include cabling the potentiometer in reverse (was expected), having a diode badly placed (more problematic) and connecting the piezo to the output instead of the input (confusing left and right duh !).

Debugging

Finished PBAs

 

 

 

 

 

 

 

 

 

 

 

This is the densest design I made this way. I begin to feel the limit and a desire to do things differently. I will change the technique for the next designs. In fact I might revisit the first modules I made, shrinking them in the process.
 

On the side

Here it is. Bottom left.

The completed case

 

And here are some sound examples where the module microphone is used for sound effects. Electric bass and synth pads are treated by the synth through the jack input.

Jay F. · Should I Come In

Finally, should you be interested, the schematics and layout.

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.

Jay F. · Happy Melodies (testing my logic module)

Connection layout

Patch of the day

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.

Experimenting

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.

Layout

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.

Jay F. · Sloth Chaos

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

Synth suitcase bottom row

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.

Assembled

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.

Jay F. · Slew Limiter on a Bass Pattern

Power Supply For Korg Volca

For the last post of 2018, I wanted to write about the making of a small power supply for 4 Korg Volca.

Power supply inside

A Korg Volca can be powered by batteries or by a dedicated power supply : the Korg KA-350.  Not only is that power supply expensive compared to the affordable Volca, but it is over-dimensioned and you end up using one per box.
Moreover, Korg uses a slightly different connector than most 9V guitar pedals power supplies and the polarity is reversed (positive inside).  They correspond to the EIAJ-02 japanese standard.  Size is 4.0 x 1.7mm.

Power plug assembly in progress

There are some solutions out there, like alternative power supplies, adapters, daisy chain cables, etc.  Nevertheless, I couldn't resist to make my own power supply.

Bob screws the cables

This is a classical dual regulated power supply.    I used a design from the excellent Sonelec website.  You'll find the layout below.

The transformer is a 220V to 2x 12V transformer.  Bridge rectifiers are DB205.  Regulators are LM317.  The power plugs are PP-014 from CUI.  The enclosure is a 137x97x67mm ABS Polycarbonate Power Supply Case.

Splices

I bought the 5 connectors from Mouser and the plastic enclosure from Banzai Music.  All the other parts are leftovers from previous projects : I usually buy a little more each time to cover losses, destruction or to simply fill my drawers just in case...

Each one of the two outputs of the power supply is split in two with splices and a bit of heat shrink tube.

The transformer is only rated for 12 VA, which means 500 mA per output.  Volca are reported to draw about 80mA. This means a total of 160 mA per output.  That's enough safety margin for me.



That's it.  Let the fun begins.

Circuit and layout

DIY-101 synth voice - part 2

This is the second part of the making of my Doepfer DIY synth based module.  You can find the first part here.

Finished module in action.

Now is the time for some cabling.

There are 7 connectors on the circuit, numbered JP1 to JP7.  Moreover, I have to connect the 5V and common ground.
With the synth, I  ordered the set of dedicated flat cables to ease the interconnection.

I started with Ground, 5V and all connections that were not linked to a specific connector.

Before cabling connectors.

Pin 1 above

Then I did cable connector after connector, cutting the wires, splitting the flat cable, stripping with my nails and finally soldering … One wire at a time, in order not to lose track. 
I started with JP2 and JP3, as I reckoned they connected mostly to pots and jacks below the circuit and that would prove difficult if I finish with them.
All ground pins on those connectors were ignored as I chose to have a common ground from the 5V power connector.

Pin 1 below

Thanks to the schematics from M-19, I noticed the dot indicating the first signal (red line) on the connector was sometimes above or below in the Doepfer documentation tables.   I fell in the trap on my first schema.

Ongoing cabling

I also verified twice each wire connection before soldering.  And I did well. I noticed a couple of mistakes on my schematics this way.  I annotated my drawings along the way.

 

 

Annotated schematics

Bob checks a solder joint

 Bob managed to get some useful Quality Control time. 

My first tests showed I made some minor mistakes :
- switches pins are reversed with regards to the switch handle position;
- a couple of signals were wrongfully soldered on the switch pin of the jack, instead of the tip;
- I detected one or two bad solder joints that escaped Bob's control.





Here is the finished product.

Finished

Bob fixes knobs.

Finally, I let Bob place the knobs.









Tuning the VCO proved problematic.  Even after I let the board heat up for 20 minutes, I really had a hard time approaching the 1V/oct slope.
I'm not 100% sure yet, but the VCO is not very stable and slowly drifts, even with the tempco option installed.  Is the circuit defective ?  Is the design problematic ?  Was it damaged during my early tests with a home made power supply ?  I don't know.  The rest works like a charm.

Tuning the beast

Finally, all the Eurorack power flat cables I got for my DIY modules were 16-pin to 16-pin.  And JP1 is aligned in a way it is not possible to use a 16-pin connector properly.

I had to divert the 10-pin to 16-pin cable from Rings to put the module in place.

Time to buy some 16-pin to 10-pin cables next time I guess.




Finally in place.   Ready to wiggle.