What is it? The Silent Switcher is a solution for powering your small-signal audio circuits with quiet, low noise and efficient power, totally separated from the mains. Audio projects are steadily getting smaller and the power supply with its transformer and rectifier and reservoir caps remain as large and looming as ever. I had been looking at switched-mode power supplies before and was never quite satisfied, but that has recently changed a lot for the good. The very high requirements for tablets and smart phones have driven switcher technology to incredible quiet and low noise performance. Also, linear (post) regulator performance has leapfrogged those old audio standby’s like the LM137/337 series.
What does it for me? Almost any small signal audio project will benefit from a Silent Switcher. A RIAA phonon preamp; a line preamp with or without tone controls, an active filter, buffers, cross-overs. Electronic volume controls, headphone amps; anything that has op amps in it. Op amp and discrete audio circuits almost always run at +/-15V, and even if the are designed for say +/-12V or +/-16V, they will almost always run fine at +/-15V. At 150mA (or more, see below at powering options) it’s enough for all but the most power hungry circuits. The 6/5/3.3V output would be ideal for a DAC or streamer with a dedicated controller. The 0.5A current (up to 1A with extra power option, see below) goes a long way to power a dedicated unit with a display, some relays, LEDs, etc.
Silent Switcher is a very high performance turnkey power supply for such mixed systems. The linear post-regulators have a PSRR of over 60dB at more than 1MHz – exactly what is needed to clench what little ripple remains from the switcher. I also put a lot of effort in designing the PCB to avoid excess radiation; very low impedance ground- and current paths, sort traces, decoupling caps right at the source, etcetera.
The Silent Switcher is not a kit: you will receive a fully assembled and tested board.
Outputs Analog circuitry mostly wants to be fed with +/-15VDC, so that was the target for my design. But increasingly the analog is combined with something digital, a DAC, a microcontroller, LEDs, relays, etcetera. So, the Silent Switcher outputs +/-15VDC at up to 150mA each, as well as a jumper-selected 6V, 5V or 3.3 output at up to 0.5 amp (see below for higher-power options). The 6V option is handy in case you want to regulate locally to 5V or 3.3V.
Connectivity There are 2- and 3-pin headers on the PCB to connect the load, and a 2-pin header for an On/Off switch. The connection to the 5V source is through a B-type USB connector or a standard 2-pin screw-type connector block. You can mount the PCB on the back of your enclosure with a hole cut out for the USB-B – no further input wring required. (The pic shows the prototype with a screw-terminal). The assembled and tested board will be delivered with a separate USB-B connector and 2-pin screw terminal, so you can mount the connector that fits your need.
Supplying the supply The Silent Switcher runs from a standard 5V/2.1A USB charger. For total separation from the mains, run it from a Power Bank. And you can also use a wall wart or (LiPo) batteries, anything between 3V and 10V will do (higher voltage allows higher out out currents – see below). The start-up of the various parts of the Silent Switcher is timed such that the inrush current doesn’t get above 2.5A, even at max load
Some numbers:
- Outputs (analog): +15 and -15 VDC at 150mA* each;
- Output (6/5/3.3V): selectable 6, 5 or 3.3 VDC at 0.5A*;
- Output noise (analog): see graph below;
- Output noise (6/5/3.3V): less than 1mV broadband
- Output impedance (analog): less than 10mΩ (+15V) and 80mΩ (-15V) at 20kHz (see graphs below);
- Output impedance (6/5/3.3V): less than 3mV drop with 100mA current step.
*The current specs (150mA at the +/–15V and 0.5A at the 6/5/3.3V simultaneously) are such that they can be used with a standard 5V/2.1A USB charger. They are not actual limits; if you use a higher input voltage source like batteries (max 10VDC) or a wall wart delivering 9V at 2A, the available output currents are doubled.
Read More: The Silent Switcher, A Quiet Mains-free Power Supply