Regulated Linear Power Supply for Raspberry Pi 4

Having recently converted to the church of Rasberry Pi, I was very pleased to find that I could squeeze even more out of my little music streamer, by adding a decent power supply.

The MCRU power supply replaced a battery system, and brought not just convenience but a great enhancement to the quality of the musical reproduction. On initial use, the most obvious improvement was with stereo imaging. The sound stage widened and each player and singer took a better defined position within it.

With further listening it has become apparent that there is more detail and and an even more life-like quality to the music. Finally, a slight sharpness, that could make the Pi system fatiguing to listen to for a long time, has been removed. In summary, the combination of the Rasberry Pi, a dedicated plugin DAC and the MRCU regulated linear power supply makes the most natural and wonderful music to have filled my music room.

Mr R. Nichols | April 2015

MCRU and Longdog Audio have developed a regulated linear power supply based on the multi award winning 2 case design which was reviewed by Hi-Fi Choice magazine and award 5 stars and a recommended badge.

Here is a review of the 5V power supply we sent to Hi-Fi Choice.

Our power supplies improve sound quality based on 100’s of satisfied customer feedbacks. The raspberry Pi and Pi 2 requires 5V DC to power it, it can be powered by the voltage from a USB socket but this can be noisy, using a fully regulated design will enhance performance and get the very best audio sound from the Pi when used as a music source.

The Pi uses a micro USB socket for power, we supply a DC plug to micro USB adpater cable to connect the linear psu to your Pi.

The design rational from Longdog founder Nick Gorham is below.

When thinking of regulation, it’s worth remembering the Roman god Janus. Who was the god of gateways, and was a two faced god looking in both directions. Likewise a good voltage regulator is required to look in both directions at once. From one direction you have the mains supply, with the ever increasing noise, distortion and random variation that exists on our household mains supply. In the other direction you have the device you are supplying power to. The load will be asking constantly varying current, and the job of the regulator will be to ignore the varying load and to supply a rock steady voltage that ignores the changing load.

To ask a single regulator to perform both tasks means that it can not do either as well as it could. We don’t ask our regulators to be two faced, we split the two functions into two separate regulators and put them both where they can do the best job.

The first regulator is close to the mains supply, its job is to take the incoming mains and convert it into a low(ish) noise DC supply, and to isolate the mess that is our household power lines from what follows. In most power supplies on the market, the output of the first stage would be directly connected to the load device, and that would certainly be an improvement over the supplies that most manufactures provide. But we can do better by adding the other face of Janus to the system.

The second regulator is supplied with a clean low noise supply, and its job is to handle the changing demands of the load. To do that, it needs to be as close to the load as possible. So we remove the second regulator from the main box, and place it close to the load, both electrically and physically, that removes it from the noise and interference of the mains supply, and allows it to spend its time looking towards the load. Typical commercial voltage regulator chips are general purpose devices, but are not quiet enough for the task on hand, so the second regulator uses a bespoke regulator based on a low noise multi stage filtered voltage reference, a low noise error amplifier and a high current low resistance mosfet. To allow it to handle the changing load it also needs to supply current on demand, so all the remaining space in the second regulator is filled with low impedance capacitors to act as a local energy source.

Using the two stages of regulator, we achieve a noise floor equal or better than most battery supplies, and a effective source resistance of the order of 0.02 ohm (and the short cable run to the load avoids increasing this valve by adding copper where its not needed, and the use of a discrete regulator design allows that tiny value to be maintained way above the frequency any audio device operates at.