The Universal Filament Regulator is a power supply that features ultra-low output noise. It is intended for powering heaters and filaments in vacuum tube amplifiers but it also serves in other applications where a low-noise power supply is needed. Such applications include high-end DACs and Raspberry Pi media streamers.

A regulated filament supply results in a dramatic reduction in mains hum in tube amps. The result is complete silence between tracks and a much cleaner tone. This is especially true when used in combination with the 21st Century Maida Regulator.

Technical Documentation

Design Documentation

• Description
• Specifications
• Performance Graphs

• This sixth revision of the Universal Filament Regulator takes an 8-17 AC input from a transformer and provides a DC output voltage in the range of 0.8-21 V, selectable in 0.1 V increments by rotary switches. It can also operate with a DC input voltage (8.0-24 V).

  The Regulator can provide up to 6 A of output current and up to 70 W of output power. The output current can be limited to 3 A by fitting a jumper. The built-in soft start ensures a gentle startup suitable even for fragile directly heated triode (DHT) filaments.

  The Universal Filament Regulator is a buck/boost regulator, which means it can provide the full output voltage range as long as its input voltage is within the specified range. That said, the best noise performance is obtained when the input voltage is higher than the output voltage.

  The Universal Filament Regulator is a high-efficiency, switching power supply. The switching frequency is 400 kHz – well above the audio band. Furthermore, it uses spread spectrum dithering to further minimize switching noise and EMI. It offers the same sonic benefits as linear regulators, including constant current regulators, without any of the bulk.

  The four-layer circuit board with 2 oz (70 µm) copper thickness requires no heat sink and will fit just about anywhere with its diminutive size (76.5 x 45.0 x 24.0 mm).

  The Universal Filament Regulator is Made in Canada.

  

• The specifications for the Universal Filament Regulator Rev. 6.0 are tabulated below.

  Parameter	Value	Notes
  Absolute max. input voltage	17.6 V	RMS, AC
  Input voltage range	8.0 - 17 V	RMS, AC
  Input voltage range	8.0 - 24 V	DC
  Output voltage range	0.8 - 21 V	Selectable by rotary switch
  Output voltage tolerance	±2 %
  Output current limiter	3 A, 6 A	Typical, jumper selectable
  Minimum load current	0 A
  Max. output power	70 W
  Output noise	3.0 mV, RMS	Vin > Vout, 800 kHz BW
  Output impedance	1.2 mΩ	Vin < Vout, DC
  Output impedance	1.7 mΩ	Vin > Vout, DC
  Line Regulation	68 dB	Vin < Vout, DC
  Line Regulation	78 dB	Vin > Vout, DC
  Switching frequency	400 kHz	Spread-spectrum
  Dimensions & weight	76.5 x 45.0 x 24.0 mm 55 g

• The Universal Filament Regulator Rev. 6.0 operates with very high efficiency, especially at the higher output power levels. The graph below shows the efficiency vs output power for both boost (V_out > V_in) and buck (V_out < V_in) mode.

  

  The Regulator provides the lowest output noise when its input voltage is higher than its output voltage. This is shown below.

  

  The output noise is a bit higher when the Regulator operates in boost mode as seen below.

  

  Note, however, that the output noise is actually quite low - only a few mV - in either operating mode.

  The measurement below shows the change in output voltage as the load current is changed from 0.5 A to 1 A in boost and buck mode, respectively. As seen, the regulator responds to the changing load very quickly and without tendency to overshoot.