NGF-E Project: White and coloured noise, random voltage

NGF-E Project: White and coloured noise, random voltage PCB

NGF-E Project: White and coloured noise, random voltage PCB

This is the noise module for my Next Generation Formant project. It is a combination of two original Elektor Formant modules. The Noise module from Elektor Formant book one and the Coloured Noise (CNC) module from book two. It provides a white noise output, a fixed coloured noise output, a variable coloured noise output “red” “blue” and a random voltage output. The noise is derived from the reverse biased BE diode of an NPN transistor.

The documentation for download can be found in my website.

NGF-E Project: White and coloured noise, random voltage schematic

NGF-E Project: White and coloured noise, random voltage schematic

Noise source is the reverse biased BE diode of NPN transistor Q1. The following operational amplifier IC1A and IC1B amplifies the noise to 10Vpp. IC1C is the buffer for the white noise output. The high pass filter C5/R23 and R13/R19 in the feedback loop of IC1D provides a bass boost for the fixed coloured noise output. IC2B is configured as a 12dB low pass. So you get a low frequency random voltage. The changing speed is set with P1A/P1B which sets the corner frequency of the low pass filter. IC2A / LED1 makes the fluctuation visible. Tr1 adjust the brightness of LED1. In the feedback loop of IC3B is an adjustable filter combination which gives you a wide range of adjustable coloured noise with P1 and P2. The output is buffered with IC3A.

NGF-E Project: White and coloured noise, random voltage faceplate

NGF-E Project: White and coloured noise, random voltage faceplate

NGF-E Project: White and coloured noise, random voltage

NGF-E Project: White and coloured noise, random voltage

NGF-E Project: 24dB LP / HP

NGF-E Project: 24dB LP / HP VCF

NGF-E Project: 24dB LP / HP VCF

This is my take on the 24dB LP / HP VCF. This filter type is widely used in many synthesizers. Because this one is for my Next Generation Formant project i started with the original Elektor Formant schematic and added my changes to the design. All parts are updated to today (2017/7) available parts. The connections are the same as in the original to keep the possibility for internal wiring. If you don’t need those features just leave them out. This PCB provides all basic functions as in the original Elektor Formant. The additional functionality is put on an add-on board. The CA3080 are replaced with LM13700. The LP/HP switch is replaced with DG419 to avoid wiring problems. The signal level is raised to 10Vpp for a better signal to noise ratio. The exponentiator for generating Iabc for the OTA’s is temperature compensated. The additional function on this PCB is the linear TM input and the sign changer for the ENV input for easier use when the filter is switched to high pass mode. All other additional functions are on the add-on board. The add-on board provides voltage control for Q and the volume indicator.

The documentation for download can be found in my website.

NGF-E Project: 24dB LP / HP VCF schematic

NGF-E Project: 24dB LP / HP VCF schematic

NGF-E Project: 24dB LP / HP VCF PCB

NGF-E Project: 24dB LP / HP VCF PCB

NGF-E Project: 24dB LP / HP VCF

NGF-E Project: 24dB LP / HP VCF rear view with AddO PCB

NGF Project: Envelope Follower

This envelope follower was first build for my Shakuhachi 2 Synth project. But it is useful for any other input signal which you want to derive a control voltage from. It provides a gate and a trigger signal as well. The envelope follower is used to detect the amplitude variations of the incoming signal and produces a control voltage that resembles the variations in the input signal.

The gate and trigger signal is derived from the input signal as well. You can vary the threshold to determine at what minimum signal level the gate goes high and the trigger fires. Gate level is +5V. Trigger level is +5V/1msec.

NGF Project: Envelope follower

NGF Project: Envelope follower

The incoming signal is rectified with a precision full wave rectifier. Then feed to a low pass filter for smoothing. The given filter values here are optimized for use with the Shakuhachi, but can easily changed to your needs. The filter values affect the ripple and the timing of the output control voltage.

The gate and the trigger signal is derived from the filter output with means of a comparator. You can adjust the sense level with the threshold potentiometer. The gate is indicated with a LED. The trigger pulse is derived from the gate with an differentiator.

Envelope follower: Scope picture with square cv

Envelope follower: Scope picture with square cv

The picture above shows the control voltage of the envelope follower following a signal of 200Hz sine wave from a VCA (purple line) with a square control voltage (blue line).

Envelope follower: Scope picture with ADSR cv

Envelope follower: Scope picture with ADSR cv

The picture above shows the control voltage of the envelope follower following a signal of 200Hz sine wave from a VCA with a control voltage set by an ADSR.

Envelope follower: stuffed PCB

Envelope follower: stuffed PCB

Envelope follower: Module

Envelope follower: Module

Envelope follower: Front

Envelope follower: Front

Shakuhachi 2 Synth Project: E-Shak Interface

Shakuhachi 2 Synth Project: E-Shak Interface

Shakuhachi 2 Synth Project: E-Shak Interface

Here is the interface for my “E-Shak”. The input comes from an exoskeleton attached to a Shakuhachi. It is connected to the interface with a 10 wire ribbon cable. The exoskeleton is used as addition to the pitch 2 voltage converter and the ENV follower. Inputs are three voltages from a three axis accelerometer (x, y, z) and three touch sensitive switches (Gate 1, 2, 3). The output range foe x, y, z is adjustable in gain and volume. This gives a wide variability in usage. The three gates are 5 V. The state is indicated with LED.

Shakuhachi 2 Synth Project: E-Shak Interface schematic

Shakuhachi 2 Synth Project: E-Shak Interface schematic

The voltage from the accelerometer is buffered and level shifted in the first operational amplifier. The amplification of the second stage is adjustable so you can spread the signal range. The inputs from the touch sensitive switches are buffered and signaled with LED.

Shakuhachi 2 Synth Project: E-Shak Interface stuffed PCB

Shakuhachi 2 Synth Project: E-Shak Interface stuffed PCB

Shakuhachi 2 Synth Project: E-Shak Interface back view

Shakuhachi 2 Synth Project: E-Shak Interface back view

Shakuhachi 2 Synth Project: E-Shak Interface side view

Shakuhachi 2 Synth Project: E-Shak Interface side view

S2S Project: Pitch 2 Voltage Converter

Here is the pitch 2 voltage converter for my Shakuhachi 2 Synth project. It is based on an article in Electronotes EN#84 p5-p9 from Robert Iodice. It consist of some control logic and a 12bit DA converter. I have found a fault in the control logic and simplified the DA converter. The original only had a V/Hz output, so I added a V/Oct output.

 

Pitch 2 voltage converter: schematic

Pitch 2 voltage converter: schematic

The circuitry takes a pulsetrain and converts it to a voltage according to the frequency of the pulsetrain.

Pitch 2 voltage converter: timing diagram

Pitch 2 voltage converter: timing diagram

A clock of about 320kHz is used to drive a 12bit binary counter. The outputs of which are fed through latches and then to a 12-bit DA converter. The voltage is then converted to V/Oct characteristic with a anti-log generator. The additional circuitry is to control the timing sequence, gating the clock signal and generating a flag signal. The flag is generated when the outputs of the counter all reach a high level. This condition is reached when the input is removed or the input frequency drops below the systems lower frequency limit.

The circuit has the advantage of sampling very quickly (only two pulses required) and holding indefinitely.

Pitch 2 voltage converter: stuffed PCB

Pitch 2 voltage converter: stuffed PCB

Pitch 2 voltage converter: Front

Pitch 2 voltage converter: Front

Pitch 2 voltage converter: Back

Pitch 2 voltage converter: Back

Shakuhachi 2 Synth Project: Shak 2 pulse

This is the first stage of the pitch to voltage converter for my Shakuhachi 2 Synth project. The incoming signal from the microphone is bandpass filtered and a pulse train is derived from the signal. This is possible because the signal/waveform of the Shakuhachi is nearly sinusoidal. At least in the higher register. As you can see on the screenshot.

Shakuhachi 2 Synth Procect: Shakuhachi signal Ro kan

Shakuhachi 2 Synth Procect: Shakuhachi signal Ro kan

In the lower register you need to adjust you playing a bit. Not in pitch but in timbre. Playing a honking RO otsu will confuse the circuitry. It is hard to discriminate between the basic pitch and the overtones in the analog domain. This can be partly corrected setting a high threshold in the filter.

Shakuhachi 2 Synth Procect: Shakuhachi signal Ro otsu

Shakuhachi 2 Synth Procect: Shakuhachi signal Ro otsu

First stage if the filter is 36dB high pass followed by a 36dB low pass. They form a bandpass with the frequency adjusted to a 1.8 Shakuhachi. The filter is followed by a comparator and a differentiating circuit. After some level shifting we get a pulse train at the output with the same pitch as the sinusoidal input signal. The output is 5V and around 150 micro seconds.

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse schematic

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse schematic

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse stuffed PCB

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse stuffed PCB

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse Faceplate

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse Faceplate

Shakuhachi 2 Synth Project: Brief project outline.

I have build my first synthesizer in the late 70’s. And I am playing Shakuhachi for seven years now. Time to bring both worlds together. Here we go.

The aim of this project is to provide shakuhachi players with the means to control an analogue synthesizer simultaneously with playing the shakuhachi, without affecting the playability of the flute.

So far it consists of three main modules: the pitch-to-voltage converter, the envelope follower and the “E-Shak”. The pitch-to-voltage converter derives a voltage from the pitch played on the shakuhachi. This is used primarily to control the pitch of the VCO (which is the initial generator of waves in the synthesizer). The envelope follower provides a voltage which follows the volume of the shakuhachi, together with gate and trigger signals. These are used mainly in conjunction with the synthesizer’s VCA (which is responsible for the dynamics of the synthesizer’s signal). The “E-Shak” is an exoskeleton attached to the shakuhachi with crepe tape. It is equipped with an accelerometer with three axes and with three switches. This module provides three control voltages according to the movement of the shakuhachi, and three additional on/off switches. The usage is only limited by the player’s imagination.

Shakuhachi 2 Synth project: Block diagram

Shakuhachi 2 Synth project: Block diagram

In the block diagram you can see the basic structure of the project. The microphone signal goes to the “Shak 2 Pulse” converter and the envelope follower (ENV). The Shak 2 Pulse converter is a band pass filter followed by a zero crossing detection with adjustable threshold. The output is a pulse train with the same frequency (pitch). This pulse train is converted to a voltage according to the pitch. The output voltage is available in V/Hz and V/Oct format. The envelope follower generates the gate (+5V), the trigger (+5V/20ms) and a voltage following the amplitude of the microphone signal.
The “E-Shak” is an exoskeleton equipped with a three axis accelerometer and three touch sensitive switches. With the interface you can adjust the gain and the inclination of the accelerometer signal. It provides three gate signal (+5V) as well.

Shakuhachi 2 Synth project: stuffed flight case

Shakuhachi 2 Synth project: stuffed flight case

NGF Project: 12dB Multimode VCF

This is my take on the 12dB Multimode VCF. This filter type is widely used in many synthesizers. You can find it in Electronotes or in the SEM modules and in many others as well. Because this one is for my Nest Generation Formant project i started with the original Elektor Formant schematic and added my changes to the design. All parts are updated to today (2017/4) available parts. The connections are the same as in the original to keep the possibility for internal wiring. If you don’t need those features just leave them out. This PCB provides all basic functions as in the original Elektor Formant. The additional functionality is put on an add-on board. The The CA3080 are replaced with LM13700. The JFET transistors are replaced with OpAmps. The signal level is raised to 10Vpp for a better signal to noise ratio. The exponentiator for generating Iabc for the OTA’s is temperature compensated. The only additional function on this PCB is the linear TM input. All other additional functions are on the add-on board.

The add-on board provides voltage control for Q, a sign changer for the ENV input for easier use when the filter is switched to high pass mode and volume indicator. This will be covered in another post.

Specs and features

  • 12dB highpass filter, 12dB lowpass filter, 6dB bandpass filter, notch filter
  • Temperature compensated exponentiator
  • 10Vpp signal level
  • TM log input
  • TM lin input
  • Positive and negative ENV control (with AddOn PCB)
  • Volume display (with AddOn PCB)
  • Voltage controlled Q (with AddOn PCB)
  • Runs on +/-15V and +/-12V (with minor resistor value changes)
    NGF Project: NGF 12dB Multimode VCF stuffed PCB

    NGF Project: NGF 12dB Multimode VCF stuffed PCB

    NGF Project: 12dB Multimode VCF schematic

    NGF Project: 12dB Multimode VCF schematic

    NGF Project: 12dB Multimode VCF Front view