Inching forward…

Another long(ish) break from posting – this time mostly courtesy of some extremely nice late-spring weather and a couple of house-related DIY-projects. Just about the only thing that has moved forward (at least enough to notice) are my ICEpower 700ASC-based mono blocks (which I discussed here). A couple of weeks ago I got the mounting plates I designed for the modules + supporting circuitry which meant I could drill the chassis and start putting some mechanicals together at last.

Some of you may have guessed that this is where my BalBUF design is supposed to end up, but there was a piece missing. A matching power supply to drop the 700ASC’s 15V aux power supply to something more manageable for the OPA1632 (which gets very hot in operation). Because I was running out of space in the enclosure I wanted to use, a key design criteria was that the PSU should be “stackable” with the BalBUF board.

I quickly found what looks like the perfect device for this use – the TPS7A39 from TI – which is a dual pos/neg low-noise regulator with the right specs. Unfortunately, it is also only available in a 3×3 mm leadless package and as my odds of hand-soldering that are pretty much = 0 I dropped that pretty quickly. Instead I went for a bog-standard LM3x7-based design, but managed to squeeze it down to size because of the modest heat sinking requirements.

In a nod to “reusability”, which is something I always aim for where possible, the PSU board includes SMD resistors on the bottom in front of the caps, which means it can also be used with the unregulated supplies on the other ASX-boards such as the 50ASX and 125ASX. This means that you can use the BalBUF with any ASX-module without a separate offboard supply for the low-voltage circuitry, and because the BalBUF and the PSU stack on top of each other it should be very compact. Assuming everything works as expected with the 700ASC when I test it, I’m pretty sure that means I’ve just figured out what to do with my last remaining pair of 50ASX’es 😀

The sketch for the rear panels is also pretty much done, but given that Schaeffer/FPX panel work is getting more and more expensive I have decided not to order the rear panels “blind”, i.e. before I have tested that the monos work electrically. If this weather continues, that might be a while though 😀

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Project files: STEPS clone PSU

What is it?
The board for my “STEPS-clone” single-rail linear PSU as described here. This PSU is suitable for low-power streamers, DACs, headphone amps etc. that run on a single DC-voltage rail and require less than app. 15W maximum. This isn’t really a 100% clone of the original STEPS supply (see here), but I’ve drawn quite a bit of inspiration from the STEPS so I think the credit is well-deserved anyway 🙂

Note that the transformer primary connections are hardwired on the board, so there are separate 115V and a 230V versions of the board files.

How big are the boards?
The board measures 3.95” x 4.7” (app. 100 x 119 mm)

What is the status of the boards?
The published board files are for version 1.0 which is the version I have prototyped. There are a few minor changes I could do, but it’s mostly cosmetic and it might be a while before I get to it anyway so I have decided to publish this version.

Does it use any special/expensive/hard-to-find parts?
If you can order from Mouser, then nothing here is hard-to find. If you can’t, then the only thing that might be difficult to substitute is the Murata common-mode choke and that is optional anyway 🙂

Anything else I need to know?

• The original idea was that the board should be able to slide into a eurocard-sized enclosure (that’s also the reason for the two extra mounting holes). However, in practice this isn’t possible as the primary pins of the transformer are way too close to the enclosure walls to make this safe. My recommended enclosure is the GX1xx-types from modushop, but there are many other options. If you have more devices, you can of course use larger enclosures to hold multiple PSUs.
• The transformer secondaries are in parallel, so with the standard Talema range from 7VAC to 22VAC, it should be possible to make the STEPS with outputs from around 3-25VDC.
• The 2-pin header near the output can be used to connect a volt meter to display the output voltage (or it can be used for something else – your choice! :D).
• The solder pads on the board can be used either as test points or to tap the AC or unregulated DC-voltage from the board to another PSU board for an AUX-voltage of some sort (additional circuit, trigger voltage etc.). Remember to watch the total load on the transformer and the maximum heat dissipation in all regulators.
• You can use my spreadsheet here to calculate the adjustment resistors for various output voltages. This will show you the upper/lower limit voltages if you use a trimpot for variable output, and also the power dissipation in the adjustment resistors which you need to be careful with at higher outputs.
• The only really tricky bit of this circuit is (potentially) managing heat dissipation if your load draws a lot of power on a continuous basis. You’ll have to balance the heat dissipation in the regulator and the pi-filter resistors, while still keeping the voltage to the regulator high enough so that it doesn’t drop out – even if the mains voltage varies a bit. A little tip can be that if your load device isn’t sensitive to output voltage, then turning up the output by app. 0.5-1V will shift some heat away from the regulator. Be sure that you stay within the specs of whatever you are connecting to the PSU at all times of course!
• As usual for these circuits, you can use both standard and LDO (low-drop regulators). The low-drop types are normally not “better”, but can be a bit less tolerant of circuitry and load conditions so it’s actually better to stick with standard LM317 unless you have a good reason to use an LDO.
• The only time it really makes sense to use a 3A rated regulator (LM350 or Lx1085 types) would be if your PSU is 5-7V output with a 25VA transformer. If your output voltage is higher or the transformer is smaller, the 1.5A+ current limit of a standard LM317 (or Lx1086) should be just fine.

Downloads:
Download design files here

Related information:
1) Read the original STEPS page linked above. Even if the circuit isn’t completely the same, there is still lots of great info about the LM317 type regulators and how to get the most of them.
2) Read the manufacturers datasheet for the regulator that you are working with. Pay specific attention to recommendations around output capacitance and bypassing of the adjust pin as there are some differences between regulator models and manufacturers here.

Note: Always read the “intro post” for additional important information about my designs.

 

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 🙂

Project files: GP-PSUs v2

What is it?
Two boards for general-purpose LM317/LM337 power supplies with two rails, useable for many low-power applications (preamps, buffers, filters etc.). There are two versions, one where the +/- voltage is derived from a single AC-voltage via a voltage-doubler and one where it comes from a traditional dual-AC, two-bridge rectifier circuit.
These boards are effectively an update on the old GP-PSUs and they are based on the triple-PSUs I posted a while ago. In fact they are just the three-rail designs with the third rail removed 😀

How big are the boards?
Both board versions measure 3.925″ x 1.8″ (app. 100 x 46 mm.) and they are mechanically interchangeable.

What is the status of the boards?
Both boards are in v1.0. I haven’t actually prototyped these in this format yet, but since they are the same as the three-rail version (which I have tested) I don’t mind publishing them.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. As always with these circuits, you can use standard LM317/337 regulators or splash out on more expensive (low-dropout) types like the LT/LM/LD108x-series. My experiences with the latter parts aren’t the greatest though (instability), so unless your applications require the low-drop capability I’d just as well stick to standard 317/337-types from a reputable source. If your application requires a higher performance PSU than this, you are probably better off looking at entirely different circuits and regulators anyway.

Anything else I need to know?
Yes, pretty much a repeat of what was mentioned for the three-rail circuits:

• The diameter of the main filter capacitors is 18mm, but the dual footprint means that anything between 10mm and 18mm should be fine.
• The DIP rectifier bridges exist in versions up to 2A rated current although anything more than 1A can be a bit difficult to find. Realistically though, if you plan on drawing more than 1A from either supply the SK104-type heat sinks are probably going to be a limiting factor anyway.
• Mounting the regulators and heat sinks is a bit of a faff because there is not much space, especially if the heat sinks are 38mm or taller. My suggestion (as always) is something like this:
  • 1) Loosely assemble the regulator, the isolation components and the heatsink.
  • 2) Mount the combination on the PCB and solder the heatsink in place.
  • 3) Tighten the screw holding the regulator to the heatsink.
  • 4) Solder the regulator in place.

Downloads:
Download design files here

Related information:
Even though the regulators used here are generic types made by many manufacturers, there can be small differences in recommended parts values etc. I suggest you always consult the regulator data sheets from the specific manufacturer.

Note: Always read the “intro post” for additional important information about my designs.

Project files: Universal Triple-PSUs

What is it?
Two boards for general-purpose LM317/LM337 power supplies with three rails, useable for many low-power applications where both a +/- supply and an auxiliary voltage are needed. Examples include analog amplifier + digital/logic circuitry, microphone preamplifier + phantom voltage etc.
There are two versions, one where the +/- voltage is derived from a single AC-voltage via a doubler and one where it comes from a traditional two-bridge rectifier circuit. This design is virtually a copy of my GP-PSUs. I made some minor enhancements and added the extra rail, but it is the same basic design.

How big are the boards?
Both board versions measure 3.925″ x 2.6″ (app. 100 x 66 mm.) and they are mechanically interchangeable.

What is the status of the boards?
The “standard” board is in v1.0 and works fine. The voltage-doubled board is in v1.1 and also works fine. The two versions are completely identical except for the diode/bridge arrangement on the +/- supply. The difference in version numbers came because I originally prototyped a different (smaller) layout for the voltage-doubled version. After making the “standard” version that requires a bit more space for the rectifier bridges, I decided it was smarter if they were both the same size and then changed the layout of the voltage-doubled board to match.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. As always with these circuits, you can use standard LM317/337 regulators or splash out on more expensive (low-dropout) types like the LT/LM/LD108x-series. My experiences with the latter parts aren’t the greatest though (instability), so unless your applications require the low-drop capability I’d just as well stick to standard 317/337-types from a reputable source. If your application requires higher performance than this, you are probably better off looking at entirely different circuits and regulators.

Anything else I need to know?

• There is a jumper on the boards that links the ground on the AUX-voltage to the midpoint (0V) of the +/- supply. This is optional and probably not required for most applications but can be used for e.g. linking analog and digital ground in mixed-signal circuits.
• The diameter of the main filter capacitors is 16mm on the AUX supply and 18mm on the main supply.
• The DIP rectifier bridges exist in versions up to 2A rated current although anything more than 1A can be a bit difficult to find. Realistically though, if you plan on drawing more than 1A from either supply the SK104-type heat sinks are probably going to be a limiting factor anyway.
• Mounting the regulators and heat sinks is a bit of a faff because there is not much space, especially if the heat sinks are 38mm or taller. My suggestion (as always) is something like this:
  1) Loosely assemble the regulator, the isolation components and the heatsink.
  2) Mount the combination on the PCB and solder the heatsink in place.
  3) Tighten the screw holding the regulator to the heatsink.
  4) Solder the regulator in place.

Downloads:
Download design files here

Related information:
Even though the regulators used here are generic types made by many manufacturers, there can be small differences in recommended parts values etc. I suggest you always consult the regulator data sheets from the specific manufacturer.

Note: Always read the “intro post” for additional important information about my designs.