Mosfet stabilized High Voltage 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 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.
With the provided PCB Layout it can quickly be built at very moderate cost. There is no need for heavy and expensive Chokes!
I tested the Sound against various conventional Designs (C-L-C, C-R-C), and i think the Sound Quality is even better!
here 's the schematic:
The Transformers AC Voltage is fed to Connector X1 and is rectified by D6-D9. C3 is Charged to the Peak Voltage
By means of R2 and the cascaded Z-Diodes D2-D5 a reference Voltage is created and filtered by C1. R2 and C1 also ensure that the reference Voltage rises slowly to the desired Voltage.
The reference Voltage is fed to the Gate of the Mosfet through R1. The Source Potential of Q1 therefore is fixed to a Voltage of about the reference Voltage minus the MOSFETs GS threshold Voltage and is very stable.
D1 is needed to ensure that the maximum Gate-Source-Voltage of the MOSFET is never exceeded, and R3 limits the curent through D1 in case of a short circuit.
R1 limits the current that can be drawn by the Mosfet from C3 in case of a short circuit, and somehow affects the sound of the connected Amplifier. Typical values are from 10 to 300 Ohms, just experiment!
The desired output voltage can be set by the combination of several Z-Diodes D2-D5 and must be chosen to meet your requerements.
The Fuses are optional to protect the Transformer in case of defective input Rectifier or Input Capacitor
The PSU will withstand short time short-circuits, but R1 and Q1 will heat up quickly and be destroyed evenually.
You can use this circuit with standard transformers or with center-tap-Transformers
When using a center-tap.transformer, the center tap is connected to X1-3. The Diodes D8 an D9 must not be used in this case!
The Filament(heater) Voltage is connected to X3. R4 and R5 provide a virtual symmetrie Point if desired.
The onboard-heatsink is sufficient for 50-80mA, enough for a EL84 Power Amplifier or a headphone Amplifier. The Mosfet should be mounted with Isolation foil for security reasons!
This picture shows the PSU along with a Optimized Morgan Jones OTH Headphone Amplifier, as shown on www.headwize.com (a very rewarding Project!!!)
Additional Information,Basics,DIY Kit, Links for Schematic