Linear PSUs are better…

…aren’t they? 😀

No, I don’t really want to start up that discussion here because in my opinion it’s much more complex subject than most audiophiles believe. However, one thing that is obvious is that as more and more small audio components run on single DC rails from an external PSU (streamers, DACs, headphone amps etc.), a fairly large market for aftermarket “upgrade” PSUs has opened up. Some manufacturers (e.g. Auralic) even offer separate PSUs as upgrades themselves. Well, a linear PSU is normally a relatively simple thing so why not DIY it?

Since I now have a DAC, a preamp, a streamer and quite a few other things that run on single-rail DC this seems a worthwhile project and it’s actually been on the drawing board for a while. I did have a bit of trouble getting started on the circuit and layout though, and I didn’t manage to really break the deadlock until remembered a design called STEPS by headwize/head-fi user Tangent from (many) years ago. The design isn’t up anymore, but thankfully I managed to locate it on the wayback-machine.

It’s basically a standard LM317-based PSU, but with a few tweaks added to tease as much performance as is possible out of the LM317 regulator (or one of its many derivatives). My version isn’t a straightforward copy of the STEPS, but I owe a big thanks to the the STEPS all the same. Compared to a “normal” LM317-based circuit this one includes:

  • A simple mains filter on the primary side of the transformer.
  • A snubber circuit on the secondary side of the transformer.
  • Space for high-speed/soft recovery diodes and snubber caps.
  • Space for 2+2 18mm filter capacitors in C-R-C (pi-filter) configuration before the regulator.

Everything else looks like the “high-performance” circuit variation from the data sheet of any LM317-type regulator. The onboard transformer is a 25VA Talema PCB-mounted toroid type meaning the design should be good for most applications requiring less than app. 20W power. The 15VA type transformer will fit as well and allow for mounting in a 1U enclosure, but the constraints on heat sinking and capacitor height might then be an issue.

The pictures show the completed 12V prototype for my Arcam IRdac as well as a partially completed 16V board for an Auralic Aries Mini (a recent purchase) – I’m waiting for a transformer in the mail before I can finish that and test it 🙂

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8 Responses to Linear PSUs are better…

  1. danieldeverell says:

    Surely better than anything I’ve seen in any walwart before!

    • theslowdiyer says:

      Hi Daniel,

      You are of course correct, but if the circuitry the the PSU feeds on the inside of the device isn’t known (and it usually isn’t) then it can be hard to estimate the real benefit. Feeding clean power to a very noisy switching circuit to generate a negative voltage might be a waste of money. Of course, experimenting can never hurt 😀

  2. Walker says:

    I’m a little worried about how much power will be dissipated by the LM317 itself in the worst case. 20W with a 12V output means 1.67A. With 30V going into the LM317 that’s 18V*1.67A = 30W of heat in addition to your 20W to the load. (There are more factors to consider but this is just back of the napkin.)

    Of course I don’t know how much current what you’re planning on powering actually draws, and I don’t know if you decided to pick a lower voltage transformer (that’s a change I’d make to make it run less hot.)

    • theslowdiyer says:

      Excellent point and one of the things I have spent some time thinking about.
      I’ll expand this when I eventually release the design, but first of all the transformer secondaries are in parallel, not in series. This means for a 12VDC output I am effectively using a 12VAC transformer.
      Secondly, we have the losses in the rectifiers, the losses in the pi-filter resistors and the adjustable output voltage itself to shift heat away from the regulator and the heat sink and on to other parts of the circuit 🙂

      • Walker says:

        Oh, if you’re using it in parallel that explains everything! I was just looking at the original schematic. Thanks.

        • theslowdiyer says:

          Yes, the original STEPS design was mainly for headphone amps using 18-24VDC. This is a little more versatile since the Talemas come with outputs from 7-22VAC, so voltages from app. 5-25VDC should be workable 🙂

    • theslowdiyer says:

      Oh, and of course if the regulator was dissipating 30W as heat it wouldn’t be able to deliver 20W to the load from a 25VA transformer 😀

  3. Pingback: Project files: STEPS clone PSU | theslowdiyer

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