Power Supply Units for Tool Units

Mains Voltage and Installation

Some notes on the Mains Voltage and the Installation

The adt-audio Tool devices require a regulated supply voltage of +/- 25 V for proper operation and best possible performance. Here are some notes on the mains power supply, voltage, frequency, and the installation of the unit.

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ToolPwr-M for 2 to 3 Units
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Rear View of a 2U high Power Supply Unit

Mains Voltage and Frequency

All ToolPwr power supply units are designed for operation with 230 V / 50 Hz. Most of the units have a mains voltage selector for operation with 115 V / 60 Hz. The selector is located next to the Euro mains power inlet.

Primary Fuse

The primary fuse is part of the Euro power supply inlet. It can be replaced without the need to open the unit. Above the plug is a little drawer that holds the fuse and a spare fuse. With the ToolPwr-M, the fuses are installed in fuse holders next to the power switch. All TooPwr units use standard 5 x 20 mm fuses. Due to the high inrush current of the torodial power transformer, SLOW-BLOW FUSES MUST BE USED. If a fuse blows, replace it by the spare fuse and take care that you get the same sort. The fuse will not blow if the outputs are shorted; if units are connected to the power supply while the power supply is on; or for any other reason that will happen while using or installing the unit.

Primary Fuse and different Mains Voltage

Switching the power supply from 230 V to 115 V will double the mains current. We usually deliver the units with appropriate fuses for the country; units we send to the USA will have fuses for 115 V. If the fuse blows after switching the unit to 115 V, please replace the fuse by a fuse with the doubled current value, i. e. use a 6.3 amp fuse instead of a 3.15 amp.

Mains Voltage

The units are designed for an operation range from 215 V to 245 V, or 107 to 123 V respectively. In general, the tolerance against different mains voltages depends on the load. It is higher, when the load is low. If the mains voltage is very low, or the units are overloaded, the internal voltage regulators will drop out, which causes 100 Hz hum (or 120 Hz hum with 60 Hz mains), that will reduce the noise performance of the audio gear. In this case, you should measure the mains voltage and get in touch with us.

Humming can have many different reasons. In most cases, the reason is not the power supply but one or more ground loops in the audio installation.

If there is humming for any reason,


All power transformers of the power supply units have a special winding, the so called screen winding, that is located between the primary windings that are connected to the mains voltage and the secondary voltages. Therefore, connecting the audio devices with the protective ground is recommended but not necessary for safety reasons. In case of problems with hum, please, get in touch with us; we'll tell you how and what to check and how to proceed.

Top View of the ToolPwr-SIf the mains voltage is a lot higher than normal, the signal to noise ratio of the audio units is not affected; but the temperature of the heat sink will be higher than normal. The high mains voltages causes a higher voltage drop on the voltage regulators of the power supply; the quantity of heat produced is higher. As long as the airflow along the heatsink is sufficient, this is not critical. If the heat cannot be transported away from the power supply unit the unit will heat up increasingly until the internal overheat protection circuit is triggered and the output voltages shut down. The remaining low output voltage is not clean, the audio signal will be distorted and a high level of hum and other disturbances appears. After switching off and cooling down the unit for a while, the overheat protection is reset and the unit will function properly again.

However, if this happens there is reason to check the mains voltage and the temperature of the heat sink. A good way for checking the heat sink temperature is just to touch it after at least an hour of operation. If it is possible to touch the heat sink without jerking back, the temperature is below 50 °C / 122 °F. This okay and there is no danger for overheat at all. If the temperature is higher you should consider to improve the airflow. The best way to do so is to install a slotted blind panel below and above the power supply in the rack. In extreme situations (totally enclosed rack with no ventilation, very high room temperature, unit mounted in a rack on top of many 'hot' devices), we recommend to install a fan in the rack.

For any questions, please get in touch.

- additional Information:
    How to determine the right power supply unit? 
    Mains voltage and installation 
    Output pinning


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