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



Sunday, 30 December 2018

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

Tuesday, 4 September 2018

Venus Cloud City

I took the opportunity of August's KVR Music Cafe contest to put the last upgrade on my small modular synth to good use.



The piece combines 6 tracks, out of which 4 are from the modular.
The first part is made entirely by the modular.  Then, enter the drums, made of TR-808 samples from NI and a synth pad from Korg Wavestation softsynth.
The main melody is played by the Korg SQ-1 in random mode and relies heavily on Rings.
Winds track consists of three sounds recorded separately and stacked.  They are made thanks to a white noise source, the filter from the DIY-101 module and the phaser.
Bass drone and the other bass pattern use the Doepfer VCO and the filter.  Rampage was used as  envelope generator.  The  movements effects on the bass drone are performed thanks to TAL Filter 2, great little toy.




DAW : Reaper
Synth : Modular Synth Suitcase, Korg Legacy Collection Wavestation, NI Kontakt 808 kit
Effects : ReaEQ, ReaXComp, NI Supercharger, TAL Dub II, TAL Filter 2, TAL Chorus-60, Voxengo OldSkoolVerb, Thomas Mundt LoudMax,

Photo : HAVOC project NASA / SACD

Saturday, 1 September 2018

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.



Sunday, 26 August 2018

DIY-101 synth voice - part 1

I bought a Doepfer DIY synth nearly two years ago.
It was lying on my shelf ever since.  
This month I made a eurorack module with it.  I'll document it's making in two parts.

Close-up of the finished panel

The Doepfer DIY synth is an assembled printed circuit board that includes all the necessary functions to build a basic analog synthesizer: VCO, VCF, VCA, EG, LFO, you name it.  You can design your own synth.  All you have to do is to provide a case and all the connections to the mandatory controls : jacks and potentiometers. 

Before I could get to a finished product I'm proud of, I went into a lengthy thought process.
My first idea was to make a semi-modular synth whose functions are as close as possible to an Roland SH-101.

I tried several panel designs before deciding on the final one.











XAOC Karl Marx Stadt module provided the necessary faith that I could build a 42 HP (about 21 cm) module to house the Doepfer DIY synth.

Moreover, I was inspired by the Motherfucker-19 work from YokoBoko.  It helped me making some decisions on jack placement and avoiding some mistakes during cabling (not that I didn't do any…).  You can find description and instructions on the module modulagrid page.

As usual, I prototyped the panel on cardboard to check my placement hypothesis.  It seemed critical here.  I wanted to specifically check  the density of jacks on the low part and the room for the spacers to hold the board.
Back side of the early cardboard prototype.


Annotated paper and cardboard proto
I used my traditional way for panels : punching to locate the holes, drilling, then printing the panel, laminating and glueing it.










This time, I chose to drill the holes with a wood block beneath the panel.    It proves to be way more comfortable than my usual technique of maintaining the panel over the edge of the bench.  The panel is firmly clamped and I move the drill freely to get to the next hole.  I know, I should get a drilling press…
Holes are 6 mm for LEDS, jacks and switches and 8 mm for pots.  It is a bit large for the pots.  But it proved helpful later.


Bob cleans-up
This generated a lot of chips and dirt. Fortunately, Bob helped me to clean the mess.









Given the panel is 3U 42HP, or 212 mm x 128,5 mm, it fits nicely on an A4 sheet of paper.
It's a large sheet.  So placing it parallel to the panel edges is essential.  A small deviation could give an awful result.
I'm quite happy with the final result except the paper is one millimeter too much on the right and could have been half a millimeter lower.




Bob cuts holes

I cut the holes with an X-Acto knife.   Here again Bob gave me a hand.

This is the time to place all pots, jacks, switches and LEDs.  There are 51 of them (23 pots, 23 jacks, 3 switches and 2 LEDs).
As the holes for pots were a bit larger than needed I corrected the most obvious alignment problems by moving the pot half a millimeter here, a millimeter there.



Sorted potentiometers


Here is the final panel before cabling.

Final before cabling
Go to part 2.


Friday, 27 July 2018

Repairing my VCO

A-110-1 standard VCO

Maybe you followed this blog for a while and wondered why I didn't write more about the Doepfer A-110-1 Standard VCO that is shown on some photographs.
Or maybe you don't care.

This module is the first module I bought new  It's also the first I fried : I plugged the connector in reverse during one of my trials, before I have a case.

The module began to act odd.  Plugging its output to Rings input halted the later.  It became very hot.
I stopped everything and began to investigate.







 -12V pin of the module connected to an unconnected pin of the bus board, presumably close to ground voltage.  Gnd pin was at 12V and 12V pin at 0V.   I headed to the A-110 service manual from Doepfer to find out which parts could have been stressed.

I spotted two components that would certainly suffer to be powered in reverse (inversion of the 12V and gnd pins) : the CA3046 transistor array (IC3) and the 78L10 10V regulator (IC5).




The two components I changed.

I reckoned the two TL074 op-amps wouldn't have been stressed as they were powered between 0V and a floating voltage that would most certainly be close to 0V.  I removed them and tested them on a breadboard : they were OK.

I also checked the TL431 Reference Voltage and it gave me the proper 3V it should.  So it was OK as well.

Maybe other transistors were stressed but I have no idea how to verify without desoldering them.  The plan is to change the CA3046 and 78L10 first and test the module.


Calibrating the module.
After some difficulties to get a CA3046 (they are reported as obsolete in DIP14 package by main distributors) and de-solder the 78L10 (I guess my de-soldering braid was oxidized), I finally replaced the two parts. 
Et voila.  A quick check at the oscilloscope showed all outputs seemed fine.  Maybe only these two components were affected after all.

Finally, I re-calibrated the module, following the service manual, skipping step 1 though (too complex).


I can finally use my VCO.  End of the story.