MFOS Wave Former, 2 PCB Set

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MFOS Wave Former, 2 PCB Set

MFOS Wave Former, 2 PCB Set

product page: mfos wave former

content courtesy of ray wilson:



Features

  • Two to ten step sculptable waveform.
  • Square or sawtooth waveshape
  • Great source of new timbres
  • Wave rounding (slew) control
  • Great source of modulation

Introduction

The MFOS Wave Former is a mashup of the MFOS Ten Step Sequencer and the MFOS VCO to produce a 1V/Octave tracking arbitrary waveform generator. Both a VCO PCB and a Ten Step Sequencer PCB are required for this project. To succeed with this project you need to understand the Sequencer project and the VCO project. Only the details of mashing them up to create the Wave Former are shown here. The VCO provides the clock signal for the sequencer allowing the output of the sequencer to be used as a signal source. The VCO is being operated in a higher frequency range than normal and thus it will not track as well at high frequency as it will at lower frequencies. The integrator cap has been changed from .005uF to 470pF effectively raising the VCO's range by a factor of ten. Neither PC board requires full population as shown in the drawings below. For full details of either project please see the respective project's page.

VCO Project - Full Details

10 Step Sequencer Project - Full Details

Schematics

The schematics for both the VCO and the Ten Step Sequencer only show the components used for this project. The interconnections between the two PCBs are shown in the PCB drawings.

VCO Schematic (For use in Wave Former)

 View as PDF

For a full description of this VCO's operation see the VCO project page (link above). The main point for this project is that we are using the output of the integrator reset comparator to clock the sequencer. The output of U2-B (pin 7) must be connected to the sequencer board at the anode of D18. Also note that the RAW ramp wave generated at the output of U2-A (pin 1) must be connected to the Waveshape switch on the panel which is shown in the panel drawings below. The VCO's integrator capacitor has been decreased in value from .005uF to 470pF to raise its frequency range by a factor of ten. The calibration procedure will be the same as used for the normal VCO except that you should work with frequencies starting at about 150Hz. (i.e 150,300,600,1200,2400,4800). At higher frequencies you can expect that the VCO will go flat. The high frequency compensation will come more into play due to the higher frequency range. However there is a wide useable range of 1V/Oct tracking operation especially at lower frequencies when using all ten steps.

The VCO's integrator reset pulses at the output of U2-B pin 7 drive the clock of the sequencer's CD4017B chip. We use the VCO's CV inputs, Coarse and Fine frequency control and the sync input of the VCO. When syncing the the output of the Wave Former does not sound like the VCO does when synced but instead the frequency of the Wave Former jumps up in steps providing a very cool effect.

 

VCO PC Board Information

Parts Layout With Component Designators

Here we see where the clock signal from the VCO is connected to the Sequencer PCB. Wrap one end of the connecting wire around the anode lead of D8. The other end of the wire goes to the pad shown on the Sequencer PCB that connects to the anode of Sequencer PCB D18. See the sequencer PCB diagrams below.

The output of the ramp generator is wired to the Waveshape switch shown on the front panel wiring diagram (Point AAA).

 

Parts Layout With Component Values

 


10 Step Sequencer Schematic (For use in Wave Former)

 View as PDF

For this project much of the Sequencer circuitry has been eliminated. You can see where the VCO's comparator connects to the anode of D18 and then the positive excursions of the VCO comparator's output are fed to Sequencer circuit point CLK. This is the clock input of the CD4017B.

The common pole of the Wave Segments selector switch goes directly to the PCB point RCT. Thus the sequencer resets when it gets to the terminal count.

 

VCO Schematic

 View as PDF

The main change for this part of the schematic is that a 10K resistor is added to the Sequencer PCB (shown on the sequencer PCB diagram). One end of the resistor connects to the inverting input of U6-B and the other end gets connected to one pole of the SPST Waveshape switch. When off the output of the Wave Former has square components and when on the output consists of sawtooth components. The original ramp fed into U6-B is inverted into a sawtooth shape. The other pole of the Waveshape switch connects to the RAW ramp output from the VCO (shown on the VCO PCB diagram).

The value of the Sequencer's glide capacitor C26 gets changes to 470pf and R57 adjusts the shape of the output by integrating it resulting in rounded corners of the square components. The range of filtering works well for the audio frequency output of the sequencer used in this manner.

10 Step Sequencer PC Board Information

Parts Layout With Component Designators

Connections for the Waveshaper switch are shown here as well as the injection of the VCO's comparator output to be used for the sequencer's clock input.

 

Parts Layout With Component Values

 

Scope Shots

Mixing the VCO's ramp wave into the output of the Sequencer's voltage results in waveforms like this. The sawtooth that rides on each of the levels can be moved up and down to create interesting waveforms and timbres. The bottom trace is the VCO's ramp wave. Here we see a stepped sawtooth wave loaded with harmonics. The bottom trace is the VCO's ramp wave.
 
This wave has a mix of square waves contributing harmonics to the total waveform. The bottom trace is the VCO's ramp wave. Here we see a stepped triangle wave loaded with harmonics. The bottom trace is the VCO's ramp wave.
 
Here we are using the sawtooth shape and applying adjustable low pass filtering using the glide of the sequencer to low pass filter the output of the sequencer. The bottom trace is the VCO's ramp wave.  
  

 

Wave Former Front Panel Information

Suggested Front Panel Layout

 View as PDF

Circuit Description

 

Suggested Front Panel Wiring Diagram

 View as PDF

Circuit Description

 

Echo Rockit Project Parts List

Component Notes

All cap voltages should be 25V or more. All resistors are 1/4W 5% (1% will work fine). MFOS PC boards use dual inline IC packages. MFOS PC boards usually use 5mm (0.2") cap lead spacing unless it is obvious from the board's legend that it should be larger or smaller. I often specify axial leads for any caps mounted on the front panel but you can use radial as well by adding some wire to the leads.

A pair of 2N3904s can be used in place of the SSM2210 shown in the schematic.
A SOIC package SSM2210 or SSM2212 can be used with the surface mount pads provided.
Use an op amp with good DC specs for U1. The OP275 is not mandatory.

VCO - Reduced Parts List for using PCB in Wave Former

Qty.DescriptionValueDesignators
1  OP275 Dual BiFET Op Amp  OP275  U1  
1  SSM2210 Matched NPN Pair  SSM2210  U3  
1  TL072 Dual Op Amp  TL072  U2  
1  PN4391 N Channel JFET  PN4391  Q1  
2  High Speed Switching Diode  1N914  D1, D8  
2  Linear Taper Potentiometer  100K  R2, R3  
6  Metal Film 1/4 Watt 1% Resistor  100K  R10, R15, R18, R23, R50, R66  
4  Metal Film 1/4 Watt 1% Resistor  10K  R17, R42, R47, R71  
1  Metal Film 1/4 Watt 1% Resistor  18K  R70  
1  Metal Film 1/4 Watt 1% Resistor  1K  R34  
3  Metal Film 1/4 Watt 1% Resistor  1M  R8, R28, R69  
2  Metal Film 1/4 Watt 1% Resistor  200K  R56, R57  
2  Metal Film 1/4 Watt 1% Resistor  2K  R24, R46  
1  Metal Film 1/4 Watt 1% Resistor  4.7K  R9  
1  Metal Film 1/4 Watt 1% Resistor  475 ohm  R19  
1  Metal Film 1/4 Watt 1% Resistor  47K  R65  
1  Trim Pot 10 Turn  100 ohm  R16  
1  Trim Pot 10 Turn  100K  R11  
1  Ceramic Capacitor  .001uF  C5  
1  Ceramic Capacitor  .1uF  C8  
3  Ceramic Capacitor  100pF  C3, C17, C19  
1  Ceramic Capacitor  4.7pF  C18  
1  Silvered Mica Cap  470pF  C6  

 

10 Step Sequencer - Reduced Parts List for using PCB in Wave Former

Qty.DescriptionValueDesignators
1  +12 Volts  +12V  +12V  
1  -12 Volts  -12V  -12V  
1  CD4017 Decade Counter Decoder  CD4017  U1  
1  TL074 Quad Op Amp  TL074  U6  
10  2N3904  2N3904  Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10  
2  1N914 Sw. Diode  1N914  D18, D26  
10  LED  LED  LED1, LED5, LED7, LED8, LED9, LED10, LED6, LED4, LED3, LED2  
10  Potentiometer  100K  R75, R76, R77, R78, R79, R80, R81, R82, R83, R84  
1  Potentiometer  1M  R57  
3  Resistor 1/4 Watt 1%  10K  R59, R60, R64  
1  Resistor 1/4 Watt 1%  150K  R63  
1  Resistor 1/4 Watt 1%  20 ohm  R61  
10  Resistor 1/4 Watt 1%  200K  R65, R66, R67, R68, R69, R70, R71, R72, R73, R74  
1  Resistor 1/4 Watt 1%  20K  R64  
2  Resistor 1/4 Watt 1%  220 ohms  R1, R58  
1  Resistor 1/4 Watt 1%  2K  R17  
10  Resistor 1/4 Watt 1%  47K  R4, R5, R6, R7, R8, R9, R10, R11, R12, R13  
1  Resistor 1/4 Watt 5%  100K  R52  
1  Resistor 1/4 Watt 5%  1M  R51  
1  Resistor 1/4 Watt 5%  20K  R39  
1  Capacitor Ceramic  .001uF  C12  
3  Capacitor Ceramic  .1uF  C17, C18, C24  
1  Capacitor Ceramic  100pF  C27  
1  Capacitor Ceramic  470pF  C26  
2  Capacitor Electrolytic  10uF  C15, C22  

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Tags: pcb, mfos wave, former, , set, ray, wilson, pcbmfwaveform, music, from, outer, space analogue, synth, modules synthesizer