Saturday, 29 February 2020

Mammouth VCO

Here is my second module from Mammouth Machine : a VCO (Voltage Controlled Oscillator) to take the place of the oscillator of the DIY Doepfer based module that I plan to relegate in a box.  Having two oscillators will allow either to enlarge the sound palette (via mixing or FM), or to have two separate synthesis voices.

Finished Module
Not much more to add than for the ADSR assembly from the same producer.  Same workmanship, same (splendid) wooden, laser-cut face.  I applied the same 2 coats of transparent matte varnish.
Small detail: this kit included the flat cable to connect the module to the bus board.  Curiously, this was not the case for the ADSR.
On the bench

I did have two little problems, though.

Ongoing calibration.
First was with the kit: I received two electrolytic capacitors of 4.7uF instead of 47uF.   With another type of module, I would have smiled and soldered the 4.7uF capacitors, but a VCO needs all the power supply stability it can get.  Maybe 4.7uF is enough.  Nevertheless, I decided to replace these capacitors with the closest value I had in stock.  No 47uF in the drawer, the 100uF are too big.  Remain two 22uF capacitors which fit like a glove.

Then, a small omission in the manual: I couldn't find out how to use the tuning trimpot to calibrate the module, when it's obviously the V/oct scale adjustment, which is critical and not that easy to adjust.
Luckily I had a little help from Bob to do the calibration.

First rows.

And now, as promised, a little bit of sound :

There are two synth voices in this track.
For the first one, the two, slightly detuned, square waves from the VCO are mixed, then sent to Ripples, whose frequency is modulated by the ADSR output.
For the second voice, the sine of the Doepfer oscillator is directed to Rings, then the phaser.
The whole is mixed in the output module.

Rampage generates the two main envelopes. One triggers the other and vice-versa.  The random outputs of the Sample&Hold and the Turing Machine are used to control the rise and fall times as well as the Rings parameters.
Notes are randomly drawn by the Turing Machine and calibrated by the 2hp Tune module.

DAW: Reaper
Usual Suspects : TAL Reverb II, TAL Chorus-60

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