Pony VCO

Befaco Pony VCO

I decided to replace my two Mammouth Boutique modules with two new Befaco kits.
The wooden front panels are very cool, but they contrast a bit with the rest.  Besides, if the modules are okay, I wanted something else.

After much hesitation, I decided to replace the oscillator with the new Pony VCO from Befaco. The other alternatives were two completely different modules: Make Noise STO and Klavis Twin Waves. One for its clean sound and simplicity, the other for its possibilities. In the end, the Pony VCO was chosen for its size (only 4 HP) vs its possibilities. And it's a kit ... well ... kinda.

Pony VCO is a very complete oscillator. It can generate over 7 octaves a sine, a triangle, a sawtooth or a square. It can also be used as a low frequency oscillator if need be.
There is a Thru-Zero FM input, which means that when the modulation signal falls below zero, it continues to oscillate, reversing its phase. This technique should make for some nice metallic sounds. It has a timbre control in the form of a wavefolder for more sonic possibilities. Small but powerful.

The kit

The kit is quite simple: two switches have to be mounted and adjusted with the front panel.  You assemble the front panel.  And that's basically it. The rest are surface mounted components already mounted.

Given the narrowness, the ten or so soldering operations needed require some dexterity and attention.

 

 

Bob calibrates

Then comes the calibration. The kit includes a small card with a QR code leading to the manual. Great idea. Except that the manual is incomplete and does not contain the necessary illustration to know where to measure the reference voltage. Fortunately, the complete manual is available on the product page.

The calibration does not pose any particular problem.

 

 

In the rack

With the two Music Thing Modular modules, the bottom row is starting to take its final shape.
Note that I took advantage of my purchase at Befaco to order a synth Duster, a handy anti-static duster and bananuts, those coloured minijack nuts to change the look of my Befaco modules and my Erica Synth filter. Befaco has a new colour code, with black nuts for the inputs and red for the outputs. Beautiful and practical.

My bottom row is getting complete.

Nearly finished botom row

And finally, a small sound illustration.  It is made of two main parts. The first is the sine output of the Pony VCO, modified by its timbre and the Twin Drive, filtered by Ripples and animated by Tides and Rampage. This is about the first minute of the sound bite. It is detailed in the patch notes below.
For the second part, a PWM wave is split into high and low frequency parts by a multi-mode filter and animated by Tides and Rampage envelopes. The sum of the two is then passed through Rings, then Beads in stereo mode.

Jay F. · The Machine (Part 2)

 

 

Patch of the first part of the track

 

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

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.