Power Supplies
Almost every piece of electronic gear needs a power supply. Here I present some simple solutions especially suited for audio applications.
Linear PSU Excel Calculator
An Excel sheet which will greatly help (or rather speed-up) the design of linear PSUs. Based on several input values (such as transformer secondary voltage, filter capacitor values, output current and output voltage) it will calculate important parameters such as regulation headroom, regulator dissipation and transformer power rating.Standard Linear PSU With Phantom Power
standard_linear_psu_r1.pdf
standard_linear_psu_r1_PCB.pdf
This is my standard PSU I use to power microphone preamplifiers. Shown are values for ±18 V (audio circuits), +48 V (phantom power) and +5 V (LEDs and relays). The design is however easily modified for different supply voltages—the Excel file linked above might help you with the required calculations. Check the pictures as well.
A custom power transformer is recommended to provide the required four secondary windings. A static and magnetic shield will greatly reduce radiated and conducted hum and noise. I usually order them from Haufe, see a picture from a recent project.
Discrete Series Voltage Regulator
discrete_series_voltage_regulator_r1.pdf
While IC regulators are cheap and easy to implement discrete designs allow substantial improvements with respect to noise and regulation; this is mainly because of the availability of large capacitors to filter the voltage reference noise, the availability of good-quality PNP transistors and the allowance of a rather large quiescent current. Output noise was measured as 700 nVrms (400 Hz—22 kHz). A complementary negative regulator is easily derived from the shown schematic.
48 V DC-DC Converters
48V_box_r1.pdf
48V_DC-DC_50mA_r1.pdf
Deriving +48 V along with dual rail voltages such as ±18 V from standard linear PSUs tends to be a nuisance as it will either require two power transformers with different secondary voltages (which is bulky and heavy), a custom power transformer with three secondary windings (my preferred but expensive approach) or voltage doubler/tripler circuits (very inefficient and sometimes unreliable).
The schematics linked above provide a valuable alternative—a simple DC-DC converter for +48 V. The first schematic will power two channels from a 9 V battery while the second schematic (which is untested) will provide phantom power for 4 to 8 microphones (depending on their current draw). Given careful layout, component placement and grounding these circuits will give an output voltage with low noise and ripple.
Resources
HB206-D.PDF
Covers extensively the basics of power supply design.
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The designs described on these pages are not commercial in any way. This means that I do not sell PCBs, kits, or anything like that. It also means that any for-profit use of the information on these pages is strictly prohibited—you may not sell PCBs, kits (neither partial, nor complete) or finished (or unfinished) units of the designs on this site, without the express written consent of Samuel Groner/SG-Acoustics.
Disclaimer
Notice that all information, schematics, layouts etc. are supplied as is, and that I can in no way be held responsible for its accurateness, functionality or even safety. Samuel Groner/SG-Acoustics shall not be responsible and disclaims all liability for any loss, liability, damage (whether direct or consequential) or expense of any nature whatsoever, which may be suffered as a result of, or which may be attributable, directly or indirectly, to the use of or reliance upon any information, links or service provided through this website.