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So I've got a few older pcbs for a low voltage tube headphone amp I built years ago - the Millett Hybrid - and was thinking I could put one together with my Pi3,IQAudio hat DAC, and WD passport HDD all in the same small enclosure and run it off the HPA's supply to use at work. The HPA needs 24VDC/750mA. I currently use the Pi/hat/hdd as a player using a 5V/2A pi wallwart.

Is there a good way to drop the 24VDC to 5VDC to run the Pi/DAC/HDD without massive heat dissipation? Also, would I need to look at filtering the power to the Pi to keep the noise down since both the amp and Pi will be tied to the same PS?

I used a LM317 regulator with a 24VDC wallwart for the amp I built in the past. It was well filtered and worked well (Tangent TREAD regulator). I thought maybe that for the amp and a buck converter for the pi. My concern is any noise from the buck.

The whole thing will be going in a 6” x 9” enclosure. The amp pcb is 4x6”. Here are some pics of my old amp (it’s just the top half enclosure) with the small regulator and the bare pcb in the enclosure for size reference.

LM317 regulator

Amp

bare pcb

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  • Not sure if this will pass as "on topic", but: You shouldn't have any issues using a 24-5 SMPS for your RPi here. They often use SMPS in audio amplifiers, so there's no reason you couldn't use it to power your RPi. Pay attention to wiring layout & see the RPi is not "starved" for power with small-gauge wiring.
    – Seamus
    Jan 27 '21 at 5:42
  • I’d like to fit everything into the enclosure. Is there an smps that is smaller than 2.5” x 4”?
    – Blooze
    Jan 27 '21 at 15:00
  • Oh yeah - thousands of them I'd guess. Have a look at Mouser, or Arrow Electronics - or any of the larger US distributors. If you're not familiar & knowledgeable on electronics in general, I would suggest you avoid the "junk traders" at Amazon, eBay, etc... they're not all selling junk, but it might be hard to tell the junk from the quality.
    – Seamus
    Jan 27 '21 at 20:12
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Look for a stepdown converter. You can get them by the kilo on ebay. I've been using them for quite many years on industrial applications. You can get them for like 2-3£ and they are small... The one I was looking was Size: L_59mm * W_21mm * H_17mm Now days I am using the ZB15-24-5S. It's a bit pricier but it's pcb mounted and I was looking for something that was on a steady supply and of-course something that can accept more than 24V input. Example

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Using a buck converter would be a good solution however be sure your 24V supply can support the additional current. Better, if you can tap into your power supply before the linear regulator, that would help but be sure the buck converter can handle that voltage with some room to spare. Hopefully the diodes you used in the rectifier circuit are bigger than one amp and the transformer can handle the additional load. This second approach would keep everything cooler as the additional energy will not have to pass through the linear regulator.

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Here is the completed unit. It works fine, except for some noise from the Raspberry Pi Zero wifi or bluetooth when the music is not playing. Even on very soft music passages you cannot hear the noise. Only when the player is stopped. I tried using a very good linear 5V supply to the Pi and it did not make a difference. Tried a Pi3 and the noise went away so it's definitely the Zero. Unfortunately the Pi3 wouldn't work in the space I had available.

I have a power shutdown for the pi on the front of the unit and a main power switch on the rear panel. I added a USB jack so as to be able to pull music directly off of a flash drive if I didn't want to stream. Tubes are 12FK6.

Millett Pi Top Millett Front

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