Deftaudio Two Channel CV Gate Attenuator for Eurorack

Two channel gain and max voltage passive attenuator with three options available:

• Basic version, two channel with 3.3V, 5V limits, precise adjustment and LED control
• Indicator version, two channel with 3.3V, 5V limits, precise adjustment with a vintage arrow indicator per channel
• Voltmeter version, two channel with 3.3V, 5V limits, precise adjustment with a single digital LED voltmeter

Description:

This is simple and efficient board to adjust voltage level when interfacing between Eurorack gear and to the outside world. It's specifically important for Gate levels, which exceed typical voltage level of 3.3V or 5V and go all the way up to 12V. While modular gear typically designed to handle those voltages, other instruments such as sync or arp inputs on vintage synths may not have a protection at all.

This board designed in mind with three modes of operation which are not available in other products:

• 3.3V logic limit. This mode is protected by a Zener diode and meant for interfacing to 3.3 logic gear, such as microcontrollers, Arduino, Teensy, etc.
• 5V logic limit. This mode similarly has a Zener diode circuit for 5V logic of the majority synthesizers sync, arpeggiator and other various trigger inputs.
• Attenuation. In this mode multi-turn potentiometer sets the attenuation ratio. While two other modes set the max voltage limit, in this mode the output voltage is linearly scaled down to the attenuation ratio set.

Purchasing options:

• PCB only: Only PCB board is included, other parts, such as connectors, diodes, resistors and LEDs are sourced by a buyer.
• DIY Kit: Comes with all parts including arrow indicators or digital voltmeter per selected option. Soldering is required.
• Fully assembled: Includes everything per selected option.

Basic version assembly instructions:

The board is self explanatory but Github link includes schematics, board layout and photos to help if there are any problems. Here are several notes though:

• Beginner soldering skills required. There are no high expectations, but being able to read schematics and understand polarity of components are quite important.
• It's highly advised to populate only parts of the schematics that you're planning to use. i.e. for 3.3V fixed limiting populate R2+D1(ch1) / R5+D5(ch2) and for 5V R1+D2(ch1) / R4+D6(ch2).
• Do not populate R1 and R2 (or R4 and R5 for ch2) at the same time or if you're not planning to use fixed limiting at all. This creates unnecessary load on the input (up to 50mA)
• Follow polarity orientation for LEDs. Square pad on PCB is for the negative pin.
• Set J3 and J5 jumpers: 1-2: fixed limit for 3.3V logic, 3-4: fixed limit for 5V logic, 5-6: Attenuation (set by RV1, RV2), 7-8: Passthru, no change.
• LEDs are active in all modes and can handle up to 12V input voltage

Indicator version assembly instructions:

The board is self explanatory but Github link includes schematics, board layout and photos to help if there are any problems. Here are several notes though:

• Beginner soldering skills required. There are no high expectations, but being able to read schematics and understand polarity of components are quite important.
• It's highly advised to populate parts of the schematics that you're planning to use. i.e. for 3.3V fixed limiting populate R2+D1(ch1) / R5+D5(ch2) and for 5V R1+D2(ch1) / R4+D6(ch2).
• Do not populate R1 and R2 (or R4 and R5 for ch2) at the same time or if you're not planning to use fixed limiting at all. This creates unnecessary load on the input (up to 50mA)
• R3/R6 are for indicator calibration. Use 470 Ohm for red area = 9V, or 220 Ohm for red = 5V
• JP1/JP2 enables the arrow indicator per channel. Note, as it also consumes some current you may expect to see some voltage drop when it's used.
• Set J5 and J6 jumpers: 1-2: fixed limit for 3.3V logic, 3-4: fixed limit for 5V logic, 5-6: Attenuation (set by RV1, RV2), 7-8: Passthru, no change.

Voltmeter version assembly instructions:

The board is self explanatory but Github link includes schematics, board layout and photos to help if there are any problems. Here are several notes though:

• Beginner soldering skills required. There are no high expectations, but being able to read schematics and understand polarity of components are quite important.
• It's highly advised to populate parts of the schematics that you're planning to use. i.e. for 3.3V fixed limiting populate R2+D1(ch1) / R5+D5(ch2) and for 5V R1+D2(ch1) / R4+D6(ch2).
• Do not populate R1 and R2 (or R4 and R5 for ch2) at the same time or if you're not planning to use fixed limiting at all. This creates unnecessary load on the input (up to 50mA)
• JP1 sets the channel for Voltmeter: 1-2 - Channel 1, 2-3 - Channel 2, no jumper = not connected
• Note: LED Voltmeter min input voltage is 2.5V (max 32V)
• Note: Voltmeter consumes ~50mA. Depends on the circuit it can be high load for some Gate implementations
• Note: As voltmeter is powered form the input circuit this can create a voltage drop when it's used
• Set J5 and J6 jumpers: 1-2: fixed limit for 3.3V logic, 3-4: fixed limit for 5V logic, 5-6: Attenuation (set by RV1, RV2), 7-8: Passthru, no change.

Andrei Kudryavtsev, Deftaudio 2008-2023.