The voltage regulator design below deals with high voltages — LETHAL voltages. If you are not comfortable or qualified to deal with these potentially deadly voltages, please do not attempt to build this circuit. Proceed at your own risk, expense, and responsibility.
Since its release in 2012, the 21st Century Maida Regulator has become widely adopted by DIY tube amplifier enthusiasts appreciating its ultra-low noise floor and extremely high ripple regulation. In this second revision of the circuit, I take its performance to a whole new level.
Regulator Impact on Sound Quality
When used in tube amplifiers, single-ended and push-pull designs alike, the 21st Century Maida Regulator results in remarked improvements in sound quality. Most commonly, builders report:
- Much bigger sound stage.
- Firmer and punchier bass.
- Huge, open, and natural midrange.
- Clearer and more precise treble.
- Zero hum.
These properties are the direct result of the low output impedance, low noise, and phenomenal ripple rejection offered by the 21st Century Maida Regulator.
The 21st Century Maida Regulator is also being employed in commercial builds with stellar results. For example, you can read Don Sachs’ impressions of the regulator here: Don Sachs Consulting – Custom KT88 Amplifier.
The 21st Century Maida Regulator offers the following features:
- True floating regulator design.
- Ultra-low output impedance across the audio band.
- Phenomenal ripple rejection.
- ±10 % adjustment range on output voltage.
- Soft start.
- Capable of start-up into a purely capacitive load (up to 47 µF verified).
- Start-up into harsh load (2.2 A inrush light bulb load).
- Handles high di/dt current pulses such as the ones caused by loose connections in tube sockets.
- No need for expensive and bulky high-power resistors.
- Optimized thermal performance.
- Ultra-low supply inductance due to the elaborate use of planes and pours.
- Small 2.25×2.6 inch (57×66 mm) board footprint.
The specifications for the 21st Century Maida Regulator are tabulated below.
|Max. Input Voltage||750 V|
|Max. Output Voltage||525 V|
|Max. Output Current||800 mA||Vin * Iout(sc) < 230 W|
|Output Impedance||< 0.06 Ω||1 kHz, Vout = 400 V|
|Residual Noise and Hum||20 µV RMS||Vout = 400 V, BW = 1 MHz|
|Output Voltage Adjustment Range||±10 %|
|Drop-Out Voltage||15 V|
|Regulator Supply Current||2.0 mA|
|Minimum Load Current||0 mA|
The input to the 21st Century Maida Regulator is a rectified DC voltage. The input voltage should be at least 15 V higher than the output voltage at all times. The 21st Century Maida Regulator is compatible with both tube and silicon rectifiers and requires only a small reservoir/smoothing capacitor in the power supply.
The extraordinary ripple rejection is shown in the oscilloscope screen shot below.
The input voltage is a full-wave rectified sine wave with a 50 µF reservoir capacitor. The load current is approximately 200 mA. The resulting ripple voltage is clearly evident and measures about 25 Vpp. The output voltage is completely free of ripple or hum – even at the highest resolution of the oscilloscope (20 mV/div). The measurement bandwidth for above measurement was 20 MHz.
- 1.0: First production version.
- 2.0: Improved routing, output impedance, line rejection, and solderability.
- 2.1: Removed C1A/C1B options for simplicity. Improved routing. Added blue solder mask and Neurochrome logo.