Scanning Mixer

Posted on January 12, 2022 by Harald

This scanning mixer is derived from the work of Jürgen Haible and Don Tillman with a lot off additions, changes and expansions.. The mixer is able to scan through four inputs with variable depth ans position. Manually and CV controlled. You can overdrive the individual channel nicely to add some overtones per channel. Rate, depth and scan amount are voltage controllable. The mixing level is controlled with sliders and voltage controllable as well. The four channels are summed into an output channel with similar controls.

The scanning mixer comes in two flavours linear and logarithmic. The linear scan gives a more smooth transition between the channels. The logarithmic scan gives a steeper separation between channels. All channels are DC coupled. So you can get interesting slowly moving CV textures when slowly scanning through different LFO outputs. When the depth potentiometer is set to zero you can use this module as simple voltage controlled mixer

Specs and features

Four input channels
DC coupled
Overdrive per channel
Variable scan depth and position
Voltage controlled rate, depth and scan amount
Mixing level voltage controllable
Power consumption below 80mA each rail

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

There are to much schematic to post here. Please refer to my website. Only pictures here.

Active Case Connector

Posted on January 9, 2022 by Harald

When using different cases it is quite inconvenient to run lots off long patch cables between them. With this pair of modules you can reduce the amount of patch cables used between cases. This modules allows to use ribbon cables between cases. The connections are active buffered with OpAmps, so they are unidirectional. To connect cases in both directions (send and return) you need two pairs of this modules.

Specs and features

Eight active unidirectional connections
Runs on +/-12V and +/-15V
Power consumption below 20mA each rail

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

**Active Case Connector: Schematic send**

**Active Case Connector: Schematic receive**

**Active Case Connector: Populated PCB**

Rotating Gate

Posted on December 6, 2021 by Harald

With this module you can distribute the incoming gate or trigger up to eight outputs. The distribution is software driven. You can select the amount of the used outputs from zero to eight with a potentiometer and an input control voltage. The potentiometer voltage and the control voltage are added together. The mode potentiometer and the mode control voltage selects the algorithm for the distribution. As for the moment (2021 Nov.) only one mode is implemented. Rotating upwards. Any suggestions or programs are welcome.

Specs and features

Gate/Trigger distribution up to eight targets.
Number of used outputs voltage controlled
Distribution algorithm voltage controlled
Runs on +/-12V and +/-15V
Power consumption below 20mA positive rail. 5mA negative rail.

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

**Rotating Gate: Schematic control board**

**Rotating Gate: Populated control PCB**

12dB Multimode VCF

Posted on November 30, 2021 by Harald

This is the Eurorack version of my NGF 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 other synthesizers as well. Nonetheless I have made some changes and adds. I wanted the filter to sound clean with no feedback and the feedback going from soft to very harsh. And usable for pinging (percussion). So I used the the CA3280 for good clean audio (You can use the newly available AS3280 instead). And added a voltage controlled feedback loop going from soft to harsh. This can give the filter a harsh sound and a lot of character. You can adjust the this behavior over a wide range with the calibration trimmers or changing one resistor and capacitor.

Specs and features

12dB voltage controlled multimode filter
Two inputs for easy mixing
Low pass, high pass, band pass and notch filter output
Positive and negative ENV control with sign changer
Temperature compensation with KTY81-110
CV inputs for linear TM, log TM, envelope, V/Oct tracking and emphasis
Runs on +/-12V and +/-15V (with minor resistor value changes for best performance)
Power consumption around 80mA each rail

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

**12dB Multimode VCF: Control board schematic**

**12dB Multimode VCF: Populated control PCB**

**12dB Multimode VCF: Populated main PCB**

Matrix Mixer

Posted on November 25, 2021 by Harald

This is a 4 x 4 matrix mixer with switches for unipolar/bipolar mode for each column. Unipolar means that the controls work as attenuators. Bipolar means that the controls work as attenuverters. In this mode the amplification is zero in the middle position of the corresponding potentiometer. Turning the knob counterclockwise from the center position the signal is subtracted from the output sum. Turning the knob clockwise from the center position the signal is added to the output sum. The module is DC-coupled and can be used for audio and control voltage mixing.

Specs and features

4×4 Matrix
Switchable unipolar or bipolar mode
Power consumption below 30mA each rail

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

**Matrix Mixer: Schematic control board**

Track (Sample) and Hold

Posted on November 19, 2021 by Harald

One more module for my Shakuhachi to Synths project. Not exclusively of course. This is a Track and Hold. Which is quite useful for other patches as well. In the Shakuhachi patch it is used to suppress an incomplete pitch to voltage conversion from the Pitch to voltage converter when the player stops blowing. The module tracks the incoming (control) voltage as long as the gate input is high. When the gate goes low the output voltage is kept. The module is DC coupled to track slowly moving voltages. For this one I have used some obsolete parts, which I had laying around. So, if you want to build it, make sure that you can get those parts. You can use it as Sample and Hold as well. Instead of a gate apply a trigger at the gate input.

Specs and features

Track or Sample and Hold
DC coupled
Gate input with LED
Signal input
Signal output
Threshold
Runs on +/-12V and +/-15V
Power consumption below 20mA each rail

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

**Track (Sample) and Hold: Populated PCB**

Shakuhachi 2 Synth Project

Posted on November 18, 2021 by Harald

**Shakuhachi to synth project: Current patch**

I have made some updates to my Shakuhachi to Synth project page. It presents the current patch and some more modules. The project is still ongoing.

Shakuhachi to synth project: Current patch blockdiagram — **Shakuhachi to synth project: Current patch, blockdiagram**

Gate Delay

Posted on November 17, 2021 by Harald

This module starts as a need for my Shakuhachi 2 Synth project. I was in need for a short Gate Delay of about 10ms (which is easy to realize). But then I thought about a more flexible solution with adjustable delay time and optional trimming the gate at the end. To be used elsewhere in the synth as well. So I came up with this solution. The hardware is still simple and the functionality lies in the software. So far I have only realized the function which I need for my Shakuhachi to Synth project. But you can easily improve about this with changing the software.

Specs and features

Gate delay with variable timing
Coarse and fine time adjustment
Gate in and out with LED signaling
End of gate trim
Runs on +/-12V and +/-15V
Power consumption below 30mA positive rail. 5mA negative rail.

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

CV Mover quad

Posted on October 8, 2021 by Harald

A companion for my other quad modules. Especially for my Quad LFO. You can use it as attenuator, attenuverter, CV Source and, most important, for offsetting bipolar control voltages to make them unipolar, positive or negative. The module is DC coupled, so you can use it for DC and AC. It is possible to offset the input with +/- 2.5V. The offset is signaled with diodes. There is an inverted output added as well. The main usage is for processing bipolar LFO voltages into unipolar control voltage inputs. If you have a LFO with +/- 5V output and want to make it unipolar set the input to halve and the offset to +2.5V. The output is then from 0..5V and 0..-5V at the negative output. You can easily adapt the module to other offset voltages with a few resistor changes.

Specs and features

Attenuator
Inverted and non- inverted output
Attenuverter
+/- 2.5V offset
Runs on +/-12V and +/-15V
Power consumption below 20mA each rail

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

CV Mover quad: scheamtic — **CV Mover quad: Schematic**

Voltage controlled AVR LFO with variable symmetry

Posted on October 7, 2021 by Harald

**Voltage controlled AVR LFO: Front view**

This is an old project dated back to December 2017. It was intended to learn some basics about the hard- and software of the ATMEGA series from AVR. It is kept simple. Just three analog inputs, one interrupt input and PWM output with filter are used. It is up to you what software you want to run on it. Here I made a simple voltage controlled VCO with variable symmetry. Speed, waveform and symmetry are voltage controlled. So you can change the triangle from ramp up to triangle to ramp down. Or make one halve of the sine very small. See screenshots below. This software was mainly written to test the hardware. To my surprise it worked sufficiently well for a LFO. So I leave it as is for the moment. No fancy accumulation with fixed point arithmetic and increment interpolation. Of course there is a lot room for improving the software. I know.