Mosfet stabilized power supply

One very important part of a tube amplifier is the power supply. It is crucial for the quality of the whole system. Especially beginners encounter problems like hum or drift that can become quite annoying. But rescue is ahead: the following circuit uses a modern MOSFET to deliver a stable and virtually hum-free voltage to power a large number of tube (and others of course) projects. This power supply unit (PSU) is used for an OTL headphone amplifier and two EL84 power amplifiers.

The power supply circuit for a tube amplifier is a critical component that directly influences the performance and sound quality of the entire system. A well-designed PSU minimizes noise and ensures stable voltage, which is essential for the proper operation of vacuum tubes that are sensitive to fluctuations in power.

In this design, a modern MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is employed due to its high efficiency and capability to handle significant power levels with minimal heat generation. The MOSFET acts as a voltage regulator, providing a clean and stable output voltage that is crucial for the operation of tube circuits.

The circuit typically begins with an AC input, which is first rectified using a bridge rectifier. This converts the AC voltage into a pulsating DC voltage. Following the rectification, a large filter capacitor is used to smooth out the pulsations, significantly reducing ripple voltage. This is vital to prevent hum in the audio output.

After the initial filtering, the MOSFET is integrated into the circuit as part of a linear voltage regulation stage. The gate of the MOSFET is controlled by a feedback loop that monitors the output voltage. If the output voltage deviates from the desired level, the feedback loop adjusts the gate voltage, thereby regulating the output voltage and maintaining stability.

Additional filtering capacitors are often placed at the output of the MOSFET to further reduce noise and ensure that the power supply delivers a clean voltage to the tube amplifier. This is particularly important in audio applications where even minor noise can be audible.

For projects involving tube amplifiers, such as the OTL headphone amplifier and EL84 power amplifiers mentioned, this power supply design ensures that the amplifiers receive the necessary power without introducing unwanted artifacts into the audio signal. The combination of the MOSFET's efficiency and the careful design of the filtering stages results in a power supply that enhances the overall performance of the audio system.One very important Part of a Tube Amplifier is the Power Supply. It is crucial for the quality of the whole system. Especially beginners encounter problems like Hum or Drift that can become quite annoying. But resue is ahead: The following circuit uses a modern Mosfet to deliver a stable and virtually Hum-free voltage to power a large number of Tube (and others of course) Projects. I use this PSU for an OTL Headphone-Amplifier and two EL84 Power Amps. 🔗 External reference