DHT filament regulator
DHT filament supply board

DHT filament regulator

I’m planning to rebuild my 4P1L paralleled amplifier. My previous was a normal DC filament supply. I wish to try filament bias this time , and I built a DHT filament power supply for 4P1L project.

From the schematic above, I used a capacitor multiplier to supply the +Ve side of filament, and another constant current source for the -Ve side. My transformer secondary windings for the filaments are 21V AC, and directly connect to bridge rectifier and smoothing capacitor . The +ve DC output of around 28V after the rectifier connected to a TIP122 darlington transistor, and capacitor on its base smoothed out the ripple, act as usual capacitor multiplier. This transistor can be replace by using any others power transistors, but prefer with hfe greater than 100, and I tested TIP41C without problem, up to 2.5A . Power mosfet also can be used without any modification, but some mosfet need to connect a zener diode between source and gate pin to protect the mosfet.

The current source are simple classic 2 transistor design. The power transistor can be replace by using others power device just like the capacitor multiplier circuit, depends on the output current we want to use. The current can be fine tune by preset on the circuit board, and the resistor R10 need to adjust to suit the current needed, the default value are suitable for around 1.3A , higher resistance will give lower current output and vice-versa.The C2 delayed a little slower than the capacitor multiplier stage, to provide slightly soft-start for the filament. The power transistors are then mount on the aluminium casing to dissipate heat.

My audiophile friends ask me why not just buy Rod Coleman DHT supply instead? I think DIY are more fun and I enjoy building it very much. I believe mine are similar to Rod Coleman’s DHT filament supply, I don’t have one and I can’t compare in detail. I found some sonic different compare transistor VS Mosfet versions though, I can’t conclude which is best but both transistor and mosfet sounds great when connected into my test amplifier, and bias using this board. I get more detail and good dynamic range, and clean background.

Once I finished rebuild my 4P1L PSE, I will share it here.

Please stay tuned!

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