Tinkering: powering a Raspberry Pi 4b from the LH Labs LPS4 linear power supply

I own the LH Labs Geek Pulse Xfi balanced DAC/headphone amplifier, along with its accompanying LPS4 linear power supply. One nice thing about the LPS4 is that it has four 12 volt outputs, so that it can power multiple devices in addition to the Pulse Xfi amp/DAC.

The Task: use the LPS4 to power a Raspberry Pi 4b, in addition to the Geek Pulse Xfi, so that I can add a simple Roon endpoint streamer to the Geek Pulse Xfi + LPS4 stack.

First challenge: what connector? While LH Labs did include extra cables with the unit, it didn't include any information about what, exactly, the connectors types might be. And the connectors look pretty delicate, so I wasn't keen on trying to reclaim a connector from the cables supplied with the LPS4. With some online sleuthing (thanks, Ghent Audio!), I discovered that the connector is a Molex Microfit 3.0 43025-0200, 3mm Pitch 2 Way 2 Row Female Straight PCB Housing. I bought a set of three from Amazon here for US$6.  Note the polarity for the LPS4 connections: negative lead on top (nearest the release clip), positive on the bottom.

Second challenge: 12v-to-5v conversion. The outputs on the LPS4 are all 12 volts. All Raspberry Pi units run on USB power at 5 volts, with the RPi4b sporting the USB C connector. So I needed a step-down "buck" voltage regulator to bring the voltage down. Fortunately, not only are these cheap, but there are plenty of units out there that already have a USB connector outputing the standard 5V. Here's the one I picked up from Amazon, for $US16, with a USB C connector and spec'd for 5V/3A power output.

Third challenge: what about amperage? The USB C standard calls for 5 volts and up to 3 amps (aka 15 watts). The LPS4 outputs are specified at 12 volts and 1.2 amps. I'm not enough of an engineer to know whether the step-down voltage regulator increases the available output amperage (voltage and amperage are related and multiplied together give you the wattage rating). I suppose it depends on the efficiency of the regulator. The good news is that it probably doesn't matter, since a typical Raspberry Pi 4b doing streaming duties is not likely to need the full recommended 2.5A, as benchmarks show that the RPi4b under load consumes only about 1.5A. The RPi also has a power LED that will let you know if you have insufficient power, by either flashing or not lighting at all.

Achievement Unlocked. After a bit of soldering (Molex connector to the voltage step-down regulator input leads), the set up works! I now have the LPS4 powering both my Geek Pulse Xfi and a Roon-ready streamer (Raspberry Pi 4b running Ropieee).

Bonus Round: powering the Allo DigiOne Signature HAT. In addition to the Raspberry Pi 4b, I also own an Allo DigiOne Signature HAT that runs on an older Raspberry Pi 3b. In order to keep electrical noise to a minimum, the DigiOne requires its own, separate, low noise USB C power source. Fortunately, the LPS4 also offers a low-noise USB A power output that powers the DigiOne HAT very nicely. (You may ask why didn't I just use that power source from the outset -- the answer is that the LPS4's USB A power connection doesn't push enough current to power a Raspberry Pi.) So, with a single cable to the wall socket, I have the LPS4 providing power to (1) Geek Pulse Xfi DAC/amp (from 12V, 1.2A output); (2) Raspberry Pi (from 12V, 1.2A output via step-down regulator); and (3) Allo DigiOne Signature HAT (from USB A). Tidy.