MFOS Minicontroller

MFOS Minicontroller


MFOS Minicontroller

product page here: minicontroller

content courtesy of Ray Wilson

This is an intermediate to advanced project and I do not recommend it as a first project if you are just getting started in synths or electronics. Only the circuit and some explanation are shown here. A lot of project building, troubleshooting and electronics experience is assumed. Additionally, electronic equipment ownership (scope, meters, etc.) is taken for granted. If you are interested in building this project please read the entire page before ordering PC boards to ensure that the information provided is thorough enough for you to complete the project successfully.

Value Change Bulletin

The value of R7 has been changed from 1M to 10M. Doing so reduces the current through R7 and subsequently increases the precision of the bus voltage when a key is pressed. A voltage divider exists between the resistor ladder and R7. By increasing the value of R7 by a factor of 10 the output of the resistor ladder is loaded less (by 10X) when a key is pressed.

Features

  • The MFOS Mini-Controller has a twenty nine note stylus keyboard (C - C - C to E)
  • It can be used to play your Sound Lab Mini-Synth or 1V/Oct modular.
  • The MFOS Mini-Controller supports four CV outputs (2 with portamento 2 without portamento) My prototype (shown) only used two.
  • There is one trigger output and one gate output.
  • Just the coolest thing EVER!

Quirks

  • Rare, rare (did I say rare) mis-sampling that grabs the raw buss voltage. Remember you are jabbing a PC trace with a piece of metal (slightly bouncy). But even so this thing is really a lot of fun to play with.

MFOS Mini-Controller MP3 Samples

Short song using the Mini-Controller.

Introduction

If you are into the synth hobby scene this is a "must have" you will be playing with this thing into the wee hours of the morning especially if you built a Sound Lab and don't already have a keyboard controller or you are planning on building a Sound Lab. This thing has added a new dimension to the fun I have with my Sound Lab. My son built one for his Sound Lab and he says he can't put it down.

More Photos

MFOS Mini-Controller Schematic Page 1 PDF

This circuit is identical to the one in the Single Buss 1V/Octave Keyboard Controller. See the circuit description there. This board has the addition of the resistors used in the keyboard voltage divider. Whereas in typical keyboard pressing a key brings the resistor divider in contact with the main buss we bring the bus to the divider via the probe used to touch the PCB pads that represent the keyboard.


MFOS Mini-Controller Schematic Page 2 PDF

This is the full resistor divider that is used to produce the 1V per octave voltage necessary to control the Sound Lab or other moddular synthesizer.

Approx. Current Consumption
+12V30mA
-12V30mA
+15V32mA
-15V32mA


MFOS Mini-Controller PCB Parts Layout Legend View (Parts Side Shown) PDF


MFOS Mini-Controller PCB Parts Layout Value View (Parts Side Shown) PDF


MFOS Mini-Controller PCB Bottom Copper (Parts Side Shown)


MFOS Mini-Controller PCB Top Copper(Parts Side Shown)


MFOS Mini-Controller PCB Top Silk Screen


MFOS Mini-Controller Front Panel and Wiring PDF

As you can see in the photos above I combined the MFOS Wall Wart Power Supply with the MFOS Mini-Controller and also fed the +12V, -12V and Ground out via banana jacks so I can power my Sound Lab Mini-Synth. It is very convenient. You only connect the PCB points shown here and of course KBUS to the banana jacks so you can connect the wand to them. There are several PCB connection points that are not used unless you score a real keyboard and then use this board to build a regular keyboard. Then you might want to use TLA (Trigger LED Anode), GLA (Gate LED Anode), and KBTP (keyboard top) as described in this article Single Buss 1V/Octave Keyboard Controller. As far as the Mini-Controller circuit is concerned when you plan to use the touch pads everything is already pre-connected on the PC board and you just leave these as they are.


KBUS Is Where The Wand Gets Connected

You connect the KBUS to the banana jacks so you can connect the wand to them.

Old Meter Probe Makes A Good Wand

I have several old meter probes lying around and they make a great wand. I suggest that you dull the tip.

Not All Board Connection Points Are Used

You only connect the PCB points shown here. There are several PCB connection points that are not used unless you score a real keyboard and then use this board to build a regular keyboard. Then you might want to use TLA (Trigger LED Anode), GLA (Gate LED Anode), and KBTP (keyboard top) as described in this article Single Buss 1V/Octave Keyboard Controller. As far as the Mini-Controller circuit is concerned when you use the key-pads everything is already pre-connected on the PC board and you do not need to connect the PCB connection points you see here with no wires going to them. Additionally if you use this PCB for a keyboard you would remove the LEDs, and the keyboard voltage ladder resistors.


MFOS Mini-Controller Project Parts List

  • Using 1% metal film resistors everywhere will reduce temperature related drift.
  • Where 1% metal film is specified 5% carbon comp will work but with more temperature drift.
  • Usually biFET amps (quads, duals, singles) can be replaced with an equivalent from another manufacturer (except for the LF444).
  • Capacitors can be film, ceramic, or silver mica.

MFOS Mini Controller Parts List

Qty.DescriptionValueDesignators
1  TL071 Op Amp  TL071  U1  
2  TL082 Dual Op Amp(s)  TL082  U2, U6  
2  TL084 Quad Op Amp(s)  TL084  U5, U4  
1  LF444 Quad Op Amp (do not sub)  LF444  U3  
11  1N914 Sw. Diode(s)  VALUE  D5, D4, D1, D2, D3, D6, D10, D7, D11, D8, D9  
1  2N3906  2N3906  Q1  
2  2N5457 N(s)  2N5457  Q2, Q3  
2  LED(s)  LED  LED1, LED2  
1  Capacitor Ceramic  .001uF  C18  
2  Capacitor Ceramic(s)  .0047uF  C25, C24  
1  Capacitor Ceramic  .01uF  C1  
15  Capacitor Ceramic(s)  .1uF  C6, C7, C9, C11, C10, C12, C13, C14, C20, C2, C3, C4, C5, C16, C22  
1  Capacitor Ceramic  22pF  C23  
2  Capacitor Ceramic(s)  470pF  C21, C17  
1  Polystyrene or Polycarbonate (low leackage) Capacitor  .01uF  C19  
3  Electrolytic Capacitor (S)(s)  10uF  C8, C15, C26  
1  Potentiometer  1M  R11  
28  Resistor 1/4 Watt 1%(s)  100 ohm  R37, R38, R39, R40, R41, R42, R43, R44, R45, R46, R47, R48, R49, R50, R51, R52, R53, R54, R55, R56, R57, R58, R59, R36, R60, R61, R62, R63  
4  Resistor 1/4 Watt 5%(s)  100K  R23, R9, R32, R33  
3  Resistor 1/4 Watt 5%(s)  10K  R15, R13, R21  
1  Resistor 1/4 Watt 5%  150K  R22  
2  Resistor 1/4 Watt 5%(s)  1K  R27, R25  
6  Resistor 1/4 Watt 5%(s)  1M  R1, R19, R20, R10, R30  
1  Resistor 1/4 Watt 5%  20 Ohm  R8  
1  Resistor 1/4 Watt 5%  200K  R34  
3  Resistor 1/4 Watt 5%(s)  20K  R24, R26, R16  
1  Resistor 1/4 Watt 5%  3.9K  R2  
1  Resistor 1/4 Watt 5%  300K  R31  
1  Resistor 1/4 Watt 5%  30K  R12  
1  Resistor 1/4 Watt 5%  39K  R4  
2  Resistor 1/4 Watt 5%(s)  3K  R28, R29  
1  Resistor 1/4 Watt 5%(s)  10M  R7 (changed from 1M to 10M Apr 2009)  
1  Resistor 1/4 Watt 5%  4.7K  R18  
1  Resistor 1/4 Watt 5%  475 Ohm  R5  
1  Resistor 1/4 Watt 5%  47K  R35  
1  Resistor 1/4 Watt 5%  82K  R6  
1  Resistor 1/4 Watt 5%  200K  R14  
1  Resistor 1/4 Watt 5%  39K  R17  
1  Multi-turn Trim Pot  1K  R3  

Miscellaneous

  • 1/16" Thick aluminum plate for mounting the pots and switches.
  • Unit is typically mounted in a synth case with other synth modules.
  • Assorted hardware 1" 6-32 nuts and bolts, 1/2" #8 wood screws, etc
  • Knobs for potentiometers, wire and solder.
  • Digital Volt Meter and a Signal Tracer or oscilloscope for testing.

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  • $37.00
  • Ex Tax: $37.00

Tags: mfos, minicontroller, analogue, synth, modules, music, from, outer, space synthesizer