Four independent LFO

Quad LFO: Front view
Quad LFO: Front view

Four independent LFO with triangle, sine, ramp up, ramp down and square wave output. Output voltage 10Vpp. The sine is inverted against the triangle. Ramp up and ramp down are twice the frequency of the triangle.

Specs and features

  • Four independent LFO
  • Triangle, sine, ramp up, ramp down and square wave output
  • Output -5V to +5V (10Vpp)
  • Runs on +/-12V
  • Power consumption below 25mA each rail

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

Quad LFO schematic
Quad LFO schematic

.Given for the first LFO. The oscillator consists of an integrator IC1C and an OpAmp Schmitt-Trigger IC1D. The triangle wave of the oscillator arises through the feedback of the trigger output to the input of the integrator. At the integrator output IC1C arises a triangle with the amplitude of the hysteresis of the Schmitt-Trigger. The input voltage of the integrator sets the rise and fall time of the voltage output. The square wave output is buffered with IC5C. The circuitry around IC4C provides the saw output. IC4D inverts the saw. The sine shaper is build with the OTA IC2OTA2 and IC3B. IC5D drives the LED.

Quad LFO schematic
Quad LFO schematic
Quad LFO waveforms screenshot
Quad LFO waveforms screenshot
Quad LFO waveforms screenshot
Quad LFO waveforms screenshot
Quad LFO populated control PCB
Quad LFO populated control PCB
Quad LFO populated main PCB
Quad LFO populated main PCB
Quad LFO side view
Quad LFO side view

Precision Adder

Precision Adder front view
Precision Adder front view

This is a useful and often needed utility module. The input voltages are precisely added to the outputs.The inputs 1, 3 and 5 are normalized. It can be used in different ways: As three independent adders, as buffered multiple, adding a modulation source simultaneously to all three outputs, adding two, three or four voltages precisely and a few more, depending on your patch. The accuracy depends on the used operational amplifier. For pitch CV I recommend precision OpAmps like the LT1014.

Specs and features

  • 3 independent precision adders
  • Input 1, 3 and five normalized
  • Buffered multiple
  • Additional common modulation inputs
  • Runs on +/-12V and +/-15V
  • Power consumption below 10mA each rail

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

Precision Adder schematic main PCB
Precision Adder schematic main PCB
Precision Adder schematic control PCB
Precision Adder schematic control PCB

All inputs are buffered with high impedance inputs. They are followed by precision adders where the two inputs and the two additional modulation inputs are added together. The last stage buffers the output and corrects the phase. Inputs 1, 3 and 5 are normalized. The accuracy depends on the used operational amplifier and the matching of the resistors. For pitch CV I recommend precision OpAmps like the LT1014. Match all 10k resistors to 0,1% or better.

Precision Adder side view
Precision Adder side view
Precision Adder populated PCB
Precision Adder populated PCB

15V to 12V adaptor

15V to 12V adaptor populated PCB
15V to 12V adaptor populated PCB

From time to time I want to integrate a 12V Eurorack module in my 15V banana setup. So I needed a 15V to 12V adaptor. Nothing spectacular. Just from the datasheet. This is the bigger brother for up to five modules from the single one.

Specs and features

  • Input +/-15V DC (or higher)
  • Output +/-12V DC

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

15V to 12V adaptor schematic
15V to 12V adaptor schematic

Just the standard configuration from the datasheets.

15V to 12V adaptor front view
15V to 12V adaptor front view
15V to 12V adaptor side view
15V to 12V adaptor side view

Buffered Multiple

Buffered Multiple front view
Buffered Multiple front view

This is a useful and often needed utility module. The input voltage is precisely reproduced on the outputs. It comes in handy when you need to distribute signals which must be decoupled. The input signal is buffered and decoupled with means of individual operational amplifiers. One input drives 6 individual outputs. The accuracy depends on the used operational amplifier. For pitch CV I recommend precision OpAmps like the LT1014 (quad) and LT1013 (dual).

Specs and features

  • 6 independent buffered outputs
  • Runs on +/-12V and +/-15V
  • Power consumption below 10mA each rail

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

Buffered Multiple schematic 01
Buffered Multiple schematic 01
Buffered Multiple schematic 02
Buffered Multiple schematic 02
Buffered Multiple side view
Buffered Multiple side view
Buffered Multiple side view
Buffered Multiple back view
Buffered Multiple populated main PCB
Buffered Multiple populated main PCB

Quad VCA, AC or DC coupled with normalized input

Quad VCA, AC or DC coupled with normalized input. Front view
Quad VCA, AC or DC coupled with normalized input. Front view

This is one more module for my quad system. It contains four VCA with normalized input, so you can distribute one input signal to four output channels. With each channel under voltage control you can move the input signal through the room dependent on the control voltages. I have two versions build one AC and the other DC coupled. Beside using this VCA’s for signal distribution you can use every VCA independently. The gain to voltage ratio is linear. This is done because it is easier to predict the performance. The distribution of the signal must be steered through the control voltages. The implementation follows the recommendations from an article at Open Music Labs from October 3, 2015 (Minimizing distortion in OTA’s)

Specs and features

  • Four VCA with normalized input
  • Usable as four independent VCA as well
  • Linear gain to voltage response
  • Individual Volume, CV and Bias controls
  • Low distortion implementation
  • Runs on +/-12V and +/-15V (with minor resistor value changes for best performance)
  • Power consumption around 35mA each rail

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

Quad VCA schematic main PCB
Quad VCA schematic main PCB

The linear controlled current source for Iabc is straight forward and implemented as usual. An elaborate description for the VCA part is given here.

Quad VCA schematic control board DC
Quad VCA schematic control board DC

On the left side are the potentiometers for volume control followed by the input buffers. The only difference between AC and DC coupling are the capacitors. On the right side are the CV input potentiometers and the bias potentiometers followed by the voltage adder.

Quad VCA control PCB AC coupled
Quad VCA control PCB AC coupled
Quad VCA control PCB DC coupled
Quad VCA control PCB DC coupled
Quad VCA main PCB
Quad VCA main PCB
Quad VCA back view
Quad VCA back view
Quad VCA side view
Quad VCA side view

Quad white and colored noise source. Quad random voltage source

Quad white and colored noise source. Quad random voltage source. Schematic control PCB
Quad white and colored noise source. Quad random voltage source: Front view

It is quite useful to have different adjustable noise and random voltage sources. Depending on your patch stile of course. Here is the quad version of my noise module from the NGF project. It is a combination of two original Elektor Formant modules. The noise module from Elektor Formant book one and the colored noise (CNC) module from book two. It provides four independent white noise outputs, four adjustable colored noise outputs with “red” and “blue” adjustment. The four random voltage outputs are adjustable in speed of change. The noise is derived from the reverse biased BE diode of an NPN transistor.

Specs and features

  • Four independent white noise outputs
  • Four independent adjustable colored noise outputs with “red” and “blue” adjustment
  • Four random voltage outputs, adjustable in speed of change
  • Four LED indicating the random voltage change
  • Runs on +/-12V and +/-15V
  • Power consumption around 65mA each rail

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

Quad white and colored noise source. Quad random voltage source. Schematic control PCB
Quad white and colored noise source. Quad random voltage source: Schematic control PCB
Quad white and colored noise source. Quad random voltage source. Schematic main PCB
Quad white and colored noise source. Quad random voltage source. Schematic main PCB

Description:

(Given for one of the four.) Noise source is the reverse biased BE diode of NPN transistor Q1 (B_090). The following operational amplifier IC1A and IC1B (B_090) amplifies the noise to 10Vpp. IC1C (B_090) is the buffer for the white noise output. IC2B (F_101) is configured as a 12dB low pass. So you get a low frequency random voltage. The changing speed is set with P3A/P3B (F_101) which sets the corner frequency of the low pass filter. IC2A / LED1 (F_101) makes the fluctuation visible. TR_1 (F_101) adjust the brightness of LED1 (F_101). In the feedback loop of IC1B (F_101) is an adjustable filter combination which gives you a wide range of adjustable colored noise with P1 and P2 (F_101). The output is buffered with IC1A (F_101).

Quad white and colored noise source. Quad random voltage source. Populated control PCB
Quad white and colored noise source. Quad random voltage source. Populated control PCB
Quad white and colored noise source. Quad random voltage source. Populated main PCB
Quad white and colored noise source. Quad random voltage source. Populated main PCB

Trapezoid quadrature VCO through zero (flat version) with waveshapers

Trapezoid quadrature VCO through zero (flat version) with waveshapers
Trapezoid quadrature VCO through zero (flat version) with waveshapers: Front view

This is my second take on the Trapezoid VCO designed by Don Tillman. My first implementation can be found here. This time I mounted the PCB’s parallel to the front to save space and integrated the wave shapers. The core is still based on the original design from Don (used with permission). I found the original article and schematic about the Trapezoid VCO on Don Tillman’s site (Link to original article from 19 July 2003). The article consists off three parts with the core implementation in part 2. I kept the basic idea and changed nearly everything else. I use an other exponentiator scheme and temperature stabilization. Another reference voltage device is used. And quadrature square outputs are implemented. As well as the additional waveforms triangle, sine, ramp up, ramp down and pulse.

Specs and features

  • Trapezoid quadrature output
  • Square quadrature output
  • Triangle quadrature output
  • Sine quadrature output
  • Pulse output, 0deg, 90deg
  • Ramp up output 0deg, 90deg
  • Ramp down output 0deg, 90deg
  • Through zero modulation
  • PWM input
  • V/Oct, FM log and trough zero CV input
  • Temperature compensated
  • Coarse and fine frequency setting
  • Runs on +/-15V and +/-12V
  • Power consumption around 135mA each rail

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

Trapezoid quadrature VCO through zero (flat version) with waveshapers: Back view
Trapezoid quadrature VCO through zero (flat version) with waveshapers: Back view

Quad output module

Quad output module
Quad output module front

This is my first step into the quad world. I want to build a system capable to deal with 4 channels. The tone control is derived from “Small Signal Audio Design” by Douglas Self second edition chapter 15. The maximum output volume is adjustable to protect your PA. You can connect the output directly to active monitors.

Specs and features

  • Bass, middle, treble tone control
  • Adjustable maximum output volume
  • Direct connection to active monitors
  • Runs on +/-12V and +/-15V
  • Power consumption around 85mA each rail

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

Quad output module schematic control board
Quad output module schematic control board
Quad output module backside view
Quad output module schematic main board

A detailed description can be found in “Small Signal Audio Design” by Douglas Self second edition chapter 15.

Quad output module backside view

Headphone output

Headphone amplifier/output front view
Headphone amplifier/output front view

Not that much to say here. Simply a Headphone amplifier. Based on Douglas Self “Small Signal Audio Design” second edition pg.560 and pg.33 fig.1.12

Specs and features

  • Drives headphones in the range from 50R to 600R
  • Runs on +/-15V and +/-12V
  • Power consumption around 25mA each rail

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

Headphone amplifier schematic
Headphone amplifier schematic

Simple dual amplifier with opamp-array (multipath amplifier).

Headphone amplifier back view
Headphone amplifier back view

Scaled voltage reference with octave and semitone steps

Scaled voltage reference with octave and semitone steps. Front view
Scaled voltage reference with octave and semitone steps. Front view

This module provides high precision CV outputs in 1V (octaves) and 83,3mV (halves) steps. The 1V output goes from -5 to +5V. The 83,3mV steps goes from -5 to plus 5 steps (halves). This module is thought for all who are missing octave switches in some modules. Especially in VCO. With this module you can switch octaves and halves as well.

Specs and features

  • High precision output 0-8V in 1V steps (octaves)
  • High precision output in 83,3mV steps, +/- 5 steps (Halves)
  • Runs on +/-15V and +/-12V
  • Power consumption around 30mA each rail

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

Scaled voltage reference with octave and semitone steps. Populated PCB
Scaled voltage reference with octave and semitone steps. Schematic

The precision voltage is derived from the REF102. The negative voltage is provided with the INA105. It is crucial to match the resistors in the voltage dividers as good as you can. The outputs of the voltage dividers are buffered to avoid loading of the dividers. The resistors around the OpAmps must be matched as well. The one volt and the 83,3mV steps are added together with IC4A. The three outputs are individual buffered.

Scaled voltage reference with octave and semitone steps. Populated PCB