New Audio-Grade Dual/Bipolar LV-Reg

This newly designed 4.5 by 4.4 inch PCB holds two low-voltage bipolar regulated power supplies. In fact, it holds two LV-Reg regulated power supplies. Why? Well, sometimes, you need two. But more importantly, this new PCB can be configured as a bipolar power supply for use with solid-state circuits. The odd fact about three-pin IC voltage regulators is that no one makes a great negative voltage regulator or, put differently, no one makes as good a negative regulator as the LD1084 is as a positive regulator. So, two positive regulators are used instead of the usual negative-positive regulator paring. How is that possible? How do you get a negative regulator out a positive one? You don’t; you make two positive regulators and stack the outputs to create a bipolar power supply by using jumpers J1 & J2.

In addition, the Dual/Bipolar LV-Reg employs two RC pre-filters, one for each regulator. Series resistors R3 define an RC filter with capacitors, C6 and C10. The resistors are 1 ohm in value and the capacitors are either 10kuF/16V or 470uF/25V or 4700uF/35V capacitors. This pre-filter defines a low-pass filter with a corner frequency of either 16Hz or 34Hz, which will greatly help strip away high frequency ripple overtones, without losing too much voltage across the resistors. If the load current is light, then a much larger-valued resistor, say 10 ohms, could be used. The Dual/Bipolar LV-Reg regulators also hold large 10uF Vishay polypropylene capacitors (C10) to bypass the outputs. (They are the black boxes you see in the photo.) In short, this is an audio-grade power supply.

The heatsinks are either 1.5 or 2.5 inches tall and provide plenty of cooling for the two LD1084 5A low-drop-out regulators. If the output voltage is greater than 20Vdc, then LM317-HV will have to be used instead, as the LDO three-pin regulators present a 30V maximum input voltage. Still, a wide range of output voltages, from +/-2.25Vdc to +/-24Vdc are possible. The rectifiers are MUR410G ultra-fast types and each is bypassed with a ceramic capacitor.

This bipolar regulator ABSOLUTELY requires a power transformer with two secondaries, as it uses two four-diode rectifier bridges. In other words, a center-tapped secondary cannot be used. Fortunately, low-voltage power transformers with dual secondaries are easy to find. Use a power transformer with a current rating at least 1.8 times greater than the expected peak load current. A fuse can be placed in series with each secondary or the primary.

The kit includes all the parts and a user guide and six hex standoffs and screw sets.