Voltage controlled LFO: Flat Version

Voltage controlled LFO front view
Voltage controlled LFO

This is the flat version of my VC-LFO I’ve build this flat version to minimize the depth of the module and avoid the wiring for the potentiometers. A VC LFO with multiple synced output waveforms is a very useful and versatile module. You can’t have enough of them. They can add a lot to sounds making them more animated. This one provides triangle, ramp up, ramp down pulse. square and sine wave output (-5V to +5V). The frequency range is easily adjusted to your needs from some minute per cycle up to 700Hz. I started with the VC LFO design form Ray Wilson MFOS but changed the exponentiator and pulse adjust schematic completely. I have added a range switch and a linear FM input as well.

Specs and features

  • Synced triangle, ramp up, ramp down, pulse, square and sine wave output
  • Output -5V to +5V
  • log and lin CV input
  • Temperature compensated
  • Voltage controlled pulse width
  • Range switch
  • Coarse and fine frequency setting
  • Runs on +/-15V and +/-12V
  • Power consumption below 10mA each rail

The documentation and the Gerber files for downloadcan be found in my website.

Voltage controlled LFO schematic
Voltage controlled LFO schematic back PCB
Voltage controlled LFO schematic
Voltage controlled LFO front PCB

C1 and associated components comprise a linear voltage to log current converter. IC1A sums the control voltages. IC1B provides the temp compensation realized with KTY81-110. TR3 adjusts the V/Oct characteristic. Q1 and Q2 forms the log converter with IC1D as constant current source. IC1C scales the control voltage for the linear FM input. The transconductance of IC1OTA1 controls the frequency of the oscillator. IC2C, C1 and associated components comprise an integrator. When current flows into IC1OTA1 output the integrator ramps up, when current flows out of IC1OTA1 the integrator ramps down. When the integrators output goes above the threshold of comparator IC2D its output goes high. The output of IC2D is fed to the non-inverting input of IC1OTA1 OTA through D1, D2, R1, R2 and TR1. TR1 balances the current flowing during the high and low periods of IC2D. With TR1 you can adjust the symmetry of the triangle. While IC2Ds output is high current flows out of IC1OTA1 OTA and the integrator ramps down until the voltage at the input of IC2D goes low enough to overcome the hysteresis provided by R13 and its output goes low. When this happens the comparator starts to ramp up again and thus we have a triangle wave at the output of IC2C. The bias of the comparator IC2D is controlled by the current generated by the linear voltage to log current convertor. This controls the current that flows in and out of IC1OTA1 and thus the frequency of the oscillator.

The sawtooth is created by mixing portions of the original triangle wave and an inverted version of the triangle wave. N-FETs Q1 and Q1 are used as analog switches.

Voltage controlled LFO screenshot waveforms: ramp up, pulse, square
Voltage controlled LFO screenshot waveforms: ramp, pulse, square
Voltage controlled LFO screenshot waveforms: triangle ramp down, sine
Voltage controlled LFO screenshot waveforms: triangle ramp down, sine
Voltage controlled LFO back view
Voltage controlled LFO back view
Voltage controlled LFO side view
Voltage controlled LFO side view

Dual PSU with 3 pole external AC input

Dual voltage PSU with 3 pole external AC input
Dual voltage PSU with 3 pole external AC input populated PCB side view

For a standalone project with a small case I was in need of an small dual voltage PSU. I can’t find a dual voltage wall wart, but I had an external AC Power Adapter from Yamaha the PA-30. The PA-30 has a 2x18V AC output with a three pole connector. So I decided to build a small PSU with the LM317L and LM337L. The design is straight forward. It is easy to expand for more current and other voltages if you need to. If you don’t want to use a external AC Power Adapter you can use a center tapped transformer.

Specs and features

  • Input: Select 3 pole AC power adapter like Yamaha PA-30 or center tapped transformer according to your needs
  • Output: +/-xV; Voltage depends on the voltage divider around LM317 and LM337. Values given here are for +/-15V.

The documentation and the Gerber files for download can be found in my website.

Dual voltage PSU with 3 pole external AC input schematic
Dual voltage PSU with 3 pole external AC input schematic

Nothing special here. Just refer to the data sheet of the LM317L/LM337L. Calculate R1/R2 and R3/R4 to your needs. The given values here are for +/-15V. Input is from a center tapped transformer or external AC Power Adapter like the Yamaha PA-30. For more current replace the LM317L/LM337L Version with the TO220 version. You’ll need to redesign the PCB then

Dual voltage PSU with 3 pole external AC input populated PCB top view
Dual voltage PSU with 3 pole external AC input populated PCB top view

12V to 5V gate converter

12V to 5V gate converter schenatic
12V to 5V gate converter front panel

This utility module converts a 12V gate to a 5V gate. It is needed when you have a module with 12V gate output and your receiving module only accepts 5V gate voltage.

Specs and features

  • Converts 12V gate to 5V gate
  • Runs on +/-12V

The documentation and the Gerber files for download can be found in my website.

12V 2 5V gate converter schematic
12V 2 5V gate converter schematic

The 12V input is divided down with the input voltage divider to 5V and buffered.

12V 2 5V gate converter populated PCB
12V 2 5V gate converter populated PCB
12V 2 5V gate converter side view
12V 2 5V gate converter side view

Send and Receive

Send and Receive front view
Send and Receive front view

As a wind player I need to keep my hands on the wind instrument. This module was first thought for connecting pedals to my modular for changing control voltages. But it is useful to include external signal changers like echo or delay or any other sound and CV source as well.

Specs and features

  • Connects a banana system to external sources.
  • Runs on +/-15V and +/-12V without changes

The documentation and the Gerber files for download can be found in my website.

Send and Receive schematic

I think you need no description here.

Send and Receive side view
Send and Receive back view

Connecting a Banana System with 3.5 Eurorack

Banana to 3.5 Eurorack front view
Banana to 3.5 Eurorack front view

This module is needed for easy connecting a banana system to a 3.5 eurorack system. It is a passive module. No signal changes are made.

Specs and features

  • Connects a banana system to 3.5 eurorack
  • Passive. No signal changes

The documentation and the Gerber files for download can be found in my website.

Banana to 3.5 Eurorack connection schematic
Banana to 3.5 Eurorack connection schematic

I think you need no description here.

Banana to 3.5 Eurorack connection populated PCB
Banana to 3.5 Eurorack connection populated PCB
Banana to 3.5 Eurorack connection side view
Banana to 3.5 Eurorack connection side view
Banana to 3.5 Eurorack connection back view
Banana to 3.5 Eurorack connection back view

24dB VCF LP/HP with gain loss compensation

24dB VCF LP/HP with gain loss compensation at high Q


VCF This is a 24dB lowpass / highpass with gain loss compensation for high Q. This one is basically derived from my 24dB VCF LP/HP which i build for my Next Generation Formant Elektor project. I just added the compensation circuitry from my Moog Ladder filter to compensate for the volume loss when Q is turned up. I have brought out all 4 filter stage outputs. Depending on your wiring you can use a switch to select between the outputs or/and bring all outputs out in parallel. The LP/HP switching is done with electronic switches on the PCB to avoid the problems (hum, noise…) of the wiring with a mechanical switch.

Specs and features

  • 24dB voltage controlled low pass and high pass filter
  • Switchable output 6dB, 12dB, 18dB, 24dB
  • Volume loss compensation with high Q
  • 10Vpp signal level
  • Voltage controllable Q
  • Voltage controlled lin and log timbre modulation
  • Positive and negative ENV control with sign changer
  • Runs on +/-15V and +/-12V (with minor resistor changes)
  • Power consumption below 60 mA each rail

The documentation and the Gerber files for download can be found in my website.

24dB VCF LP/HP with gain loss compensation at high Q: Schematic back PCB .
24dB VCF LP/HP with gain loss compensation at high Q: schematic front PCB

Straight forward design. Four state variable filter cells are connected together in series, The output of each filter cell is brought out. There are a lot descriptions of those state variable filters out there. I feel no need to add another one. The resonance (Q) is voltage controlled with means of the OTA IC2OTA1 in the upper right corner (page 1). To compensate the volume loss when the resonance (Q) is turned up a second OTA (IC2OTA2) is used. This two OTA shares the same Iabc source. The amplification of this second OTA is increased when Q is going high and add volume to the output signal.

24dB VCF LP/HP with gain loss compensation at high Q: back view
24dB VCF LP/HP with gain loss compensation at high Q: populated front PCB
24dB VCF LP/HP with gain loss compensation at high Q: populated back PCB
24dB VCF LP/HP with gain loss compensation at high Q:side view


Trigger Delay

Trigger Delay front

Trigger Delay front

This module can delay an incoming trigger signal up to 8 seconds. The trigger length is adjustable up to 8 seconds as well. The trigger pulse length is independent from the input signal length. Both parameters are independently adjusted with potentiometers. The output state is shown with a LED.

Specs and features
• Input: positive Trigger or any fast changing voltage.
• Output: 5V pulse with adjustable delay and length.
• PSU +15V/-15V or +12V/-12V

The documentation for download and the Gerber files for download can be found in my website.

Trigger Delay schematic

Trigger Delay schematic

Trigger Delay populated PCB

Trigger Delay populated PCB

Trigger Delay back view

Trigger Delay back view

CV Mover

CV Mover faceplate

CV Mover faceplate

This utility module provides you with different functions. You can use it as attenuator and sign changer for any input signal. You can use it as CV Source. It gives you a DC offset between -2.5V ans + 2.5V with coarse and fine adjustment. This voltage range is easily adopted to your needs with simple resistor change. Most interesting application is using it as “CV Mover”. This means adding a DC offset to the input signal. Say you have a LFO signal between +/-5V and want to shift it in the positive range. Then you can divide the signal in half with the attenuator to 1/2 and add the +2.5 threshold and you get a 0..5V positive LFO signal. This comes in handy for steering filters VCA’s and other modules. The output signal is visualized with LED

Specs and features
• CV source -2.5..+2.5V with coarse and fine adjustment
• Attenuator
• Positive and inverted output signal
• Adjustable DC offset for the input signal
• Positive and negative CV output indicator with LED
• Runs on +/-15V and +/-12V

The documentation and the Gerber files for download can be found in my website.

CV  Mover: schematic

CV Mover: schematic

IIC1B acts as a simple inverting voltage adder. The input signal and the offset voltages are added together. The direct output from IC1B is the negative of the input signal. IC1A converts the signal back to the original phase. IC1C is a simple buffer and in the feedback loop of IC1D are the indicator LED’s.

CV Mover populated PCB

CV Mover populated PCB

Voltmeter

Voltmeter faceplate

Voltmeter faceplate

The circuitry of this module was developed by Ray Wilson of MFOS. It was part of his Multi-Function Module. I have changed some resistor values to use with low current LED.
The LED voltage level meter gives you a graphical idea of where the voltage level you like to use to modulate your filter or VCA is. This circuit lights the LED in real time giving you a rough idea of the voltage level you are looking for. This is very useful when you want to move a CV from bipolar to only positive values.

Specs and features
• Three voltage ranges (+/-1V, +/-5V, +/-10V).
• Realtime LED display
• Runs on +/-15V and +/-12V
• Power consumption below 15mA each rail

The documentation for download can be found in my website.

Voltmeter schematic

Voltmeter schematic

IC4A is used for input buffering. IC4B and IC4C and associated components build the range selection circuitry. The heart of the circuit is the group of comparators build with IC1x, IC2x, IC3A and IC3B. The left side is used to measure the positive voltage, the right side for the negative voltage. LED 11 is the “near ground” indicator. IC3C and IC3D build a window comparator. For a more detailed description please refer to the original source at Ray Wilson’s Site MFOS (Multi-Function Module).

Voltmeter populated PCB

Voltmeter populated PCB

Voltmeter side view

Voltmeter side view

VC LFO

VC LFO front

VC LFO front

A VC LFO with multiple synced output waveforms is a very useful and versatile module. You can’t have enough of them. They can add a lot to sounds making them more animated. This one provides triangle, ramp up, ramp down pulse. square and sine wave output (-5V to +5V). The frequency range is easily adjusted to your needs from some minute per cycle up to 700Hz. I started with the VC LFO design form Ray Wilson MFOS but changed the exponentiator and pulse adjust schematic completely. I have added a range switch and a linear FM input as well.

Specs and features
• Synced triangle, ramp up, ramp down, pulse, square and sine wave output
• Output -5V to +5V
• log and lin CV input
• Voltage controlled pulse width
• Range switch
• Coarse and fine frequency setting
• Runs on +/-15V and +/-12V
• Power consumption below 10mA each rail

The documentation for download can be found in my website.

VC LFO schematic

VC LFO schematic

VC LFO waveforms screenshot

VC LFO waveforms screenshot

VC LFO waveforms screenshot

VC LFO waveforms screenshot

VC LFO populated PCB

VC LFO populated PCB