Magnus Synth Schematics

Magnus/synths/schematics

Sawtooth Frequency Doubler

This is based on a idea that I got about how to make a frequency doubler of a sawtooth. It will take a sawtooth (intended to match the ASM-1 sawtooth output), compare with 0V, weight summing and amplification.

Schematic is available in PDF.

Circuit Theory of Operation

The U1A op-amp acts like a comparator providing a 50 % PWM pulse. The PWM pulse will "raise" the lower part (-5V -> 0V) of the sawtooth and "lower" the upper part (0V -> +5V) of the sawtooth, this is done by suitably summing the sawtooth (through R1) and the PWM pulsewave (through R2). Since only the upper half of the PWM pulse is being used (due to the D1 diode) will an DC error occur and therefore will a DC correction be provided (by R3). The resulting sawtooth require amplification in order to resume the same swing as the input signal, this is provided by U1B, R4 and R5).

Part count: 1 double op-amp, 1 diode and 5 resistors.

Sawtooth Frequency Doubler V2 - has errors, use V3

This is the evolved version of the above frequency doubler. The diode is not necessary and the DC correction resistor can be dumped aswell.

Schematic is available in PDF.

Circuit Theory of Operation

The U1A op-amp acts like a comparator providing a 50 % PWM pulse. The PWM pulse will "raise" the lower part (-5V -> 0V) of the sawtooth and "lower" the upper part (0V -> +5V) of the sawtooth, this is done by suitably summing the sawtooth (through R1) and the PWM pulsewave (through R2). The resulting sawtooth require amplification in order to resume the same swing as the input signal, this is provided by U1B, R3 and R4).

Part count: 1 double op-amp and 4 resistors.

Sawtooth Frequency Doubler V3

This is the evolved version of the above frequency doubler V2. There is two errors in the V2 schematic, first the R1 and R2 resistors was swapped and the output gain was too small.

Schematic is available in PDF.

Circuit Theory of Operation

The U1A op-amp acts like a comparator providing a 50 % PWM pulse. The PWM pulse will "raise" the lower part (-5V -> 0V) of the sawtooth and "lower" the upper part (0V -> +5V) of the sawtooth, this is done by suitably summing the sawtooth (through R1) and the PWM pulsewave (through R2). The resulting sawtooth require amplification in order to resume the same swing as the input signal, this is provided by U1B, R3 and R4).

Dimensioning rules

x = V+ / Vpeak, R2 = R1 * 2 * x, R3 = R4 * (x+1)/x

Part count: 1 double op-amp and 4 resistors.

Sawtooth Phase Shifter - has errors, use V2

This is the evolved version of the above frequency doubler.

Schematic is available in PDF.

Circuit Theory of Operation

The U1A op-amp acts like a comparator providing a variable PWM pulse. The PWM pulse will counteract the initial sawtooth reset jump and insert a new reset jump. The position of the new reset jump is the result of the phase of the sawtooth (and thus voltage) and the phase CV signal. The comparator will flipp as the sawtooth raises above the CV input. The resulting sawtooth will have an error voltage which rises with the CV input, so this is compensated by hooking R4 to the CV input rather than the ground. The resulting sawtooth require amplification in order to resume the same swing as the input signal, this is provided by U1B, R3 and R4).

Part count: 1 double op-amp and 4 resistors.

Sawtooth Phase Shifter V2

This is the evolved version of the above phase shifter. It has inherrited the resistor errors of the frequency doubler, but also got the ratio between the resistors wrong so it has been corrected.

Schematic is available in PDF.

Circuit Theory of Operation

The U1A op-amp acts like a comparator providing a variable PWM pulse. The PWM pulse will counteract the initial sawtooth reset jump and insert a new reset jump. The position of the new reset jump is the result of the phase of the sawtooth (and thus voltage) and the phase CV signal. The comparator will flipp as the sawtooth raises above the CV input. The resulting sawtooth will have an error voltage which rises with the CV input, so this is compensated by hooking R4 to the CV input rather than the ground. The resulting sawtooth require amplification in order to resume the same swing as the input signal, this is provided by U1B, R3 and R4).

Part count: 1 double op-amp and 4 resistors.

V/oct to Hz/V converter

This is really the ASM-1 VCO expo converter ripped out and put into use for conversion of V/oct CV voltages into Hz/V CV voltages. The R14 resistor should be adapted to allow for correct Hz/V scale.

Schematic is available in PDF.

4069 CV-ADSR v0.1

As a wild idea I wanted to test my abilities and see if one could make an analogue synth out of only the CMOS 4069UB hex inverter chip. I allready knew there where VCO, VCF and VCA solutions using at least alot of 4069 solutions I thought that the envelope generator is the place to start. Now, it occured to me that one could actually have one 4069 set up as both variable resistor and signal switch and that this would be used to provide charging current to an capacitor. This is at this stage highly untested and just a snappshot of an idea. PDF.

2-pole State Variable Filter

This is a classic schoolbook filter which has no fancy features like CV control etc. It is usefull both as it is, but also to put next to the CV-enabled variant (such as the SEM and ASM-1 VCFs) for eductional comparisions. For completeness all outputs are buffered, but that is optional (except for the notch output, if being used). This is also a great filter to use as a base for a full parametric equalizer.PDF.