Multipurpose (Tube) Controller

Category: Product Published: Friday, 29 June 2018 Written by Richard Hoogeveen

Let's move the tube amp to the 21st century ! (or your solid state amplifier)

This pcb is the new HMR-audio multipurpose (tube) controller.

For some, digital electronics in a tube amp is an impossible combination, well not for me.  I wanted to see more information of my tubeamplifier and have more control. I created a board which can do these things. To use this board you must be able to work with Arduino IDE and have the knowledge of all kind of electronic parts and busstructures.

It can certainly be a nice circuitboard to learn and to work with different kind of components and slowly expand into a completely usable solution and then build it into your equipment.

I can give some support to a certain extend or you can ask me to do the programming for you, which ofcourse is not totally free. 


This board is based upon an Robodyn Arduino 16Mhz MegaPro 5V embed with USB interface, it is just a smaller version of the Arduino Mega 2560 but with the same functionality (go to Arduino for the MEGA 2560 specifications). 

PDF pinout of this Arduino

Not all of the Arduino pins are used (54 I/O pins, 16 Analog) for the different applications on this board, the rest is still available on the bottom of the board and can be hardwired. You can see many options are already made available on this board.


The following video is the controller programmed for the HMR-audio 2A3/300B Tube amplifier, not all Nextion screens are shown that are part of the software (shutdown, audiodetection etc.)




Board size 100 x 120mm

220V, 0.9Watt in stdby, Off mode.

5V, 4A

XH 2.54mm pitch connectors

SPI bus connector (MISO, MOSI, SCK, SS) , example bitbang registers, sensors as BPM183 barometric

I2C bus connectors, example RTC, LCD, OLED, all kind of sensors.

Mode connector input, example a switch on the back of your equipment that shortens this connector to gnd.

Manual switch connector (GND, "OFF", "ON"), when used with a 3 position switch, you can create ON, Auto (audiodetect ?) and OFF.

IR connector for connecting a IR receiver (or sender ?)

Rotary Encoder connector (digital push/turn knob, rotation A, B, S Push)

LM35 temperature sensor connector (measure your heatsink temperature ?)

DS1820 I2C digital temperature sensor connector

a BC337 transistor (max sink 800mA), for example switching a large relay

a VOM1271 Photovoltaic MOSFET driver , integrated fast turn off (Switch your HV delayed ?)


 Relay 250VAC/5A, 30VDC/5A, your ON/OFF relay ?

Optional vintage ledbar with 8 led, the most right is connected to the same signal as the relay, the others are free to wire to a positive signal (they only use 1mA)

4 x RGB led connectors (bias monitoring ?) 

Nextion touchpanel display connector (+, -, RX2, TX2)

serial ports set (RX1,TX1 and RX3,TX3) are available on pads on the board or on the bottom pins. RX0,TX0 is used by USB.

Bias connector 4 Analog inputs LA, LB, RA, RB, also known as Tube 0, 1, 2, 3 (example, measuring single or balanced currents over a resistor in a tube amp)

2 high impedance audio inputs with a rectifier circuit to measure audiosignal, L and R (audiodetection ?)

3 High Voltage input pins (1% resistor divider network, (Uin/44.1) x 0.1), 380VDC will be 0.855VDC.

Several pads 5V, GND, for peripherals

The arduino is able to store your settings in 4096 bytes of EEPROM (latest volume ? counting tube hours ?)

AREF pin, to apply your own analog reference voltage (programmable in Arduino IDE) or use the internal (Mega analogReference function)




LCD used for debugging or use it for you application

Meanwell 5V/4A, use a stable 5V ! otherwise measuring is unreliable.

RTC I2C module if you need time/calendar.


If you are looking for a real autobias controller for tubes ? It's not here, but may be soon :-)


You can contact me if you are interested in this controller.

Empty PCB/Schematics and having fun building you own stuff on it : 35 euro





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