# Magnus Synth Schematics

## Magnus/synths/schematics

This is the place where I hold various schematics of cursuits that I have made.

## 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.