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32 bit Processor is Core of Multi-function Module
The GMS-634EU Programmable Processor has a Teensy 3.1 processor board with a 32 bit ARM Cortex-M4 processor, USB interface, 96MHz clock, 512K of program memory and 65K of data memory. The supporting module includes two analog inputs with attenuators, two extra potentiometer-controlled voltage sources, 2 analog outputs supported by a two channel 12 bit DAC, two gate level inputs, two gate level outputs, a two channel in and out audio interface with a 24 bit 96 KHz sample rate CODEC, a standard 5 pin DIN MIDI input and output, and a 3.5mm stereo headphone output with level control.

By using the Arduino IDE with the Teensyduino add-in users of this module can download their own sketches to the module to utilize the processing power and substantially larger program space contained in this processor. A number of modular synthesizer specific sketches are available and can be downloaded and run in this module using the Teensy support libraries and some minor code modifications. In addition, libraries are provided to allow users to access the provided stereo CODEC as a high quality stereo audio input and output. The input and output jacks support -10dB line level signals.

The module can be purchased assembled or in kit form. The kit includes a Teensy 3.1 processor with pre-installed headers. The surface mount header that is used to access more of the processor I/O is also pre-installed. The CODEC board is supplied with pre-installed headers, too. The CODEC board has a socket for a mini-SD card, accessible from the rear of the module, and has been configured with SD card libraries in the Arduino environment.

The kit comes complete with all the parts and with the potentiometer leads pre-assembled. Even the solder is included. All the builder needs to assemble this kit is a narrow-tip soldering iron, long nose pliers, diagonal cutters, a small flat blade screwdriver to secure the knobs and a small or medium Phillips screwdriver. A wrench for tightening the pot and jack nuts is also recommended.

This kit includes complete instructions for assembly and is recommended for builders with intermediate kit building skills.
New Kit Recreates an Old Classic
The GMS-294a VC Low Pass Filter is a faithful recreation of the classic Moog 904a 4 Pole Transistor Ladder filter. It incorporates the same audio path and transistors used in the original filter designed by Robert Moog. The GMS-294a adds an attenuator on the audio input and an attenuated CV input as well as a 1 Volt/Octave frequency control input.

The manual resonance control causes a peak in the low pass response and if increased to near maximum will cause the filter to go into sine wave oscillation.

The 1 MU wide module is available either assembled or in kit form as shown here:

The kit comes complete with all the parts and with the potentiometer and jack leads pre-assembled. Even the solder is included. All the builder needs to assemble this kit is a narrow-tip soldering iron, long nose pliers, diagonal cutters, a small flat blade screwdriver to secure the knobs and a small or medium Phillips screwdriver. A wrench for tightening the pot and jack nuts is also recommended.

This kit includes complete instructions for assembly and is recommended for builders with intermediate kit building skills. Some calibration is required after assembly and minimally requires a voltmeter although a waveform display of some kind is helpful.
Dual DADSR Envelope Generator Has Multiple Modes
The GMS709a dual DADSR envelope generator, in addition to the normal ADSR controls adds a delay setting prior to the start of the envelope. The delay time interval can range from 1 millisecond to 10 seconds. Other panel controls can select an exponential envelope or a linear envelope with either positive or negative direction. The operating modes are Normal, Gated and Loop. In Loop mode, by adjusting the delay, attack and decay controls, the envelope generator will generate a series of envelopes with varying frequency.

The gate input connector also includes a trigger input on the ring connection so that a trigger source can restart the Attack/Decay phase of the envelope while the gate signal remains active. There is also a front panel gate pushbutton to trigger the envelope for each channel.
Adapter Allows Using Expert Sleeper ES-3 Module in MU
The ES3-MU adapter allows a Expert Sleepers ES-3 Mk II ADAT optical interface module designed for Eurorack to be housed and powered in a 5U MU format synthesizer cabinet. The Eurorack panel is removed from the module and some minor and reversible modifications made to the module. The module can then be remounted in the MU panel and connected to an internal circuit board that provides power and output interface connections to 1/4 inch panel jacks.

The module adapter also allows the user to select signal conditioning for the channel 5-8 outputs to produce an analog output or a 0-5 Volt standard gate output. Internal power supplies are connected to the module through a 16 pin Eurorack power cable. The module will be available as a semi-kit to allow current ES-3 MK II owners to adapt their modules. We will also offer a retrofit service for those people who want to obtain a completely assembled and tested unit.
USB MIDI to CV Converter Uses Teensy 3.1
A Eurorack compatible USB MIDI to CV converter uses the Teensy 3.1 microcontroller as its USB port and controller. The 6HP wide unit includes 2 CV channels, 2 gate channels, an isolated DIN MIDI input connector and a DIN MIDI output connector.

The control voltage output range is internally settable to 0-10 Volts or -5-+5 Volts. The gate signal is 0-5 Volts active-high. The software for the unit is open-source and can be reloaded and modified by the user. A programming development environment that utilizes the Arduino IDE with a Teensy support add-in can be used to create new functions using Arduino-like commands.

The module will be available in the Synth Store either assembled or as a complete kit. A demo program will be available that provides a two CV output and also allows USB MIDI note commands to be sent and received from the serial MIDI ports.
Let Out Your Inner DIY
The first modular synth kit will be available shortly. The GMS732EU USB/MIDI/CV module contains a board, a Eurorack panel, connectors and parts to build a support host for a Teensy 3.1 microcomputer board. The module also provides a two channel 12 bit digital to analog converter, buffer amps, two 0-5 Volt gate outputs, a MIDI input, and a MIDI/DIN clock output. Shown below is a mockup of the new module:

The panel is 5.03 inches tall and 1.20 inches wide (6HP). The depth behind the panel is less than 2.0 inches. The module is designed to be used in a standard Eurorack synthesizer case and has a IDC-16 pin Eurorack power connector. There is a jumper selectable +5 Volt regulator on-board which can be used if the Eurorack system does not provide +5 Volts. The panel will be available black painted with white screen printing or clear anodized aluminum with black lettering.

This intermediate experience level kit contains all the parts necessary for construction including solder, a USB Micro B to A cable and detailed, fully illustrated, assembly instructions. Users need to supply a medium-fine tipped soldering iron, long nose pliers, and diagonal cutters for assembly. The kit comes with a 3D printed bending gauge to allow neat bending of component leads. There are no surface mounted parts used in this kit.

The Teensy 3.1 is a powerful microprocessor card containing a 72MHz Freescale MK20DX256 Cortex-M4 processor and USB communications processor on a 3/4 inch by 1 1/3 inch PC board. It has 256KB of program memory and 64KB of RAM. There is a Teensyduino add-in available for the Arduino IDE that allow sketches developed in the Arduino enviroment to be loaded into the Teensy.

A demo program will be available for download that causes the module to perform as a USB MIDI to CV converter. It will also allow MIDI commands to use the MIDI I/O connectors. Source code for the project will be available for download.
Small Eurorack Development System
This small Eurorack system has been assembled to assist in the development of new modules and accessories for this format. Shown here is the production version of the PM Resonator for Eurorack.

Dual DADSR Envelope Generator Coming Soon
The GMS-709 Dual Envelope Generator prototype is coming along. The single MU panel will house two complete DADSR-type envelope generators. Controls will allow selection of exponential or linear ramps in either positive going or negative going outputs. Modes include normal gate, gated loop and LFO operation.

The gate input will allow a gate signal on the tip and a trigger signal on the ring of a stereo 1/4 inch jack. If the gate is high and a new trigger signal is applied, the delay, attack and decay phases will be run again.

Shown below is a mockup of the new module:

New Web Store is Back
I have set up the Grove Synth Store again. I am populating products back into the store as I get time. Most of the currently available products are listed but it will take some time to get the descriptive information reinstalled. Orders can be placed, the Paypal is working and the shipping options now include UPS and USPS.
16 Step Mini Sequencer Available for Pre-Order
The GMS777 Voltage Sequencer is a 2x8 or 1x16 step sequencer which produces a CV output and gate output per channel. Each channel has a clock input and a separate reset input. Several step functions are programmable using a push button and LED for each step. Stop and skip can be programmed for each step.

There is a separate switchable quantizer for each channel. The output voltage range 0-2V, 0-5V, and 0-10V is selectable from the panel. The module will also support the "Q" bus modules and interface.

The unit will be available in MU, in MOTM and in EURORACK configurations all running about $350.00 range. Pre-orders for delivery in March can be made through an indiegogo crowd-funding project. This will offer a couple of options including discounts and other bling. Also the purchaser will have the option of selecting knob styles including the new custom-molded Davies 1900 knobs in ivory.

Pre-orders can be placed using this indiegogo campaign.


You will receive a unit at a substantial discount, a fabulous project shirt and free domestic shipping. International participants will receive discounted shipping.