Improving the improved?

A bit of a long hiatus for me but don’t worry, nothing’s happened or anything. Simply the combination of decent summer weather and the usual “pre-holiday” panic at work, trying to get everything finished before people start taking time off during July and August. Fortunately, even though I might not be focused on diyaudio doesn’t mean that everyone else isn’t either…

As I’ve written about several times one of the things I like best about this hobby is the opportunity to get to interact with fellow DIY’ers and even “co-creating” a little bit with them. A month or so ago I was contacted by a reader called Andy who asked permission to use my STEPS-clone PCB layout as basis for a design with a “de-noisator” circuit that was being discussed on diyaudio. As I’ve already made the STEPS PCB files public there wasn’t too much to “OK” in any case but I was of course grateful to be asked and obviously also a little bit interested in the circuit as well.

The Denoisator-circuit uses a few simply components to improve the noise performance of the LM317, so while the STEPS design was already an improvement on a basic LM317-regulator circuit, it’s quite clear from the performance measurements in the thread that the De-noisator moves the performance bar even higher. And the best things about it are of course that it might actually be a bit cheaper than my original STEPS-version and also that there isn’t a single ultra-tiny, impossible-to-solder, leadless SMD package anywhere 😀

I did briefly consider taking a stab at modifying the layout myself, but I could see more work starting to come up in the horizon and as I did not really need a new PSU design so I begged off. Fortunately Andy decided to take a stab at it himself and it’s quite clear he does know his way around Eagle 🙂 To cut a long story a bit shorter a new design was made, prototype boards were ordered and Andy was gracious enough to send me one of these – and that is what landed in my postbox earlier this week.

I don’t have an immediate application for the board I received from Andy right now, but it’s clear that the next time I have a need for single-supply circuit with enough space in the box there is a decent upgrade waiting in my PCB inventory. And actually, I am now sufficiently intrigued by the “De-noisator” circuit that if I find myself thinking about designing a dual PCB with it as well at some point.

Project files: Filtered IRM power supplies (part 1)

As promised a while ago, here are my designs for the “filtered” power supplies based on IRM AC/DC modules. These are excellent for adding compact and powerful single and dual supplies which still have a reasonably good performance to any small preamp/headamp amplifier.

Read more of this post

More MeanWell IRM PSUs…

As regular readers will know I have been using the Mean Well IRM-series AC/DC PSU modules quite a lot. There are many positives to these modules (size, cost, standby consumption etc.) and only a few downsides, mostly the limited output voltage options and the rather noisy output. The noise doesn’t matter so much when used for auxiliary supplies, but for things like preamps, headphone amps etc. I’m sure it’s possible to do better.

However, because the IRMs are a switching design with a relatively high switching frequency (app. 100kHz), cleaning up the output on the IRMs should be relatively easy with just a passive “Pi”-filter (CRC or CLC). Because of the high ripple/noise frequency even a low series resistance/inductance and a little bit of extra capacitance should have a dramatic effect. Some time ago I started making a single-rail PSU based on an IRM-module for a clean and compact 5V supply for my “Music Box” project, but I realised that actually these would be applicable in many projects so I ended up with several different versions (single/dual, different power levels, integrated/separate filtering etc.)

As I’ve just received what I think is the last variant, an integrated dual version with space for two 15/20W IRMs, now seems to be a good time to collect everything and release the project files so they will be up as soon as I am back from my summer holiday in a week or so. Until then, I hope you enjoy the summer 🙂

Improving small DC-DC converters…

I’ve written a few posts about DC-DC converters and I’ve found them very useful for many circuits where a “complex” (= multi-rail with fixed voltages) power supply needs to be replaced with something “simpler” and more flexible (= single-rail with large variations allowed). However, I have previously largely ignored small SIP-type converters because I didn’t believe they were powerful enough to be of much use. As I (recently) realised you can actually get 3W from several manufacturers and even 5-6W from certain others. That makes it’s possible to get 100mA or more at +/-12-15V which is more than plenty for most small opamp circuits such as buffers, preamps and RIAAs, and of course single-rail 5-12V currents more than suitable for small auxiliary circuits in power amps etc.

Now, there are a few drawbacks to these converters: Even the small converters normally still have quite large ripple voltages and I expect there is quite a bit of HF-noise as well, but I’ve tried to use a passive filter to compensate for that. The basic idea is that because the switching frequency of the converter is very high (typically 50-100 kHz) which is nearly 1000 times higher than a linear supply, a simple passive filter is also 1000 times better at removing ripple and noise and so even small capacitor/resistor values for the filter gets you very far. A second drawback is that the converters have limited tolerance for capacitive loading, so it’s normally a good idea to think the power source into the design/build of the consumer circuit. That’s normally also doable though.

The basic SIP-8 form factor is used by several manufacturers so there are quite a few different converters to choose from, both cheap and not-so-cheap. One thing that differs between manufacturers seems to be the allowed capacitance load that the converters will tolerate. Here, the more expensive Recoms and Tracos list considerably better specs than the cheaper converters, so that’s worth looking into before you choose. Given how the converter works, this restriction mainly applies to higher voltages of 12-15V or higher – at 5V the load margin is likely to be fine even for the cheaper converters.

The boards I’ve made are both a single and a dual version with the same form factor and they both work as expected. However, after I received the boards and assembled the prototypes I had a couple of ideas to improve the filtering a bit so I’m going to hold off making the board files public until I’ve tried those ideas 🙂

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.

EDIT 21st March 2020: As described here I have added files for v1.5 below. Apart from some other minor changes, the board now includes the footprint for the 10VA Talema transformer (so you can use 10-25VA sizes) as well as an extra set of pads between the main capacitors to make space for a larger footprint inductor for the Pi-filter.

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

EDIT 21st March 2020: Download v1.5 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: IRM Switching PSUs

What is it?
Since I first discovered the IRM-series of compact switching supplies from Mean Well I’ve grown quite fond of them. They are compact, cheap and very easy to implement so they are perfect for everywhere an “aux-voltage” is required to power non-critical circuitry. Through the different applications I’ve found for these I have managed to build up a full series of boards suitable for the IRMs.

While some of the boards can be (and are intended to be) used for “serious” stuff (to be shown later on), a very obvious application for most of these boards are as AUX-supplies for powering relays, displays, logic circuitry etc. where a bit more or a bit less ripple and noise are of no consequence, but where the compact size and low standby consumption is a real plus.

There are four board versions, suitable for the IRM modules in all versions from 3-30W output power (the 30W board is missing from the pictures as I couldn’t find the prototype when they were taken – sorry! 😀 ).

How big are the boards?

  • The 3W board measures 1.8” x 1.5” (app. 46 x 38 mm.)
  • The 5/10W board measures 1.2” x 2.65” (app. 31 x 67 mm.)
  • The 15/20W board measures 1.25” x 2.95” (app. 32 x 75 mm.)
  • The 30W board measures 1.6” x 3.6” (app. 41 x 92 mm.)

What is the status of the boards?
All of the board files are version 1.0 or higher. Some tweaks have been done after the initial protoypes for a few of them, mostly because of errors/issues with the IRM module footprints.

Does it use any special/expensive/hard-to-find parts?
No, none. Several places to get the IRM-modules them selves (Mouser, Reichelt, TME etc.) and everything else on the boards is more or less optional 😀

Anything else I need to know?

  • The modules have worse specs for ripple and noise than most linear regulators, but obviously the switching frequency is quite high (66-100 kHz depending on model), which means that passive filtering like an LC or a CRC (“pi”) filter would be an ideal way of reducing the output noise. I have a couple of examples for that which I might show later.
  • I haven’t been able to find a spec for how much capacitance the modules will tolerate on the output, but it probably should not be overdone.
  • Remember that obviously one side of the board carries mains voltage, so take the necessary precautions when working with them.

Downloads:
Download design files here

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

Humble beginnings….

I thought the title was appropriate because while this build might not look like much, what comes after it is hopefully somewhat more impressive. It’s an external AC power supply (a.k. a. a transformer in a box 😀 ) for an upcoming version of Kevin Gilmore’s Dynahi SuSy (SuperSymmetry) balanced headphone amplifier (more info here).

The reason for making an external PSU isn’t grounded in any particular philosophical belief but simply in a lack of available space in an (already sizeable) amplifier chassis. The decision to make it an external AC PSU rather than an external DC PSU is a slightly philosophical one though – although heavily influenced by thoughts on practicality and versatility 🙂

This is 2x25VAC and it will eventually have a 2x30VAC identical twin for another project which also requires an external PSU – at least if it is to have any hope of fitting in a standard-sized stereo rack 😀

The chassis is as compact as I could reasonable make it and the output is fused via my fuseboard (link) and then fed to a 5-pin Neutrik XLR which has a few features I like for this application (solid, reliable, cheap, locking etc.)

Front panel, power switch and final wiring coming once the front panel layout for the amplifier itself is ready 🙂

Project files: VFET PSU

What is it?
In response to a reader request, the project files for my V-FET PSU board shown here. Of course, this will also work for any other class A design you might think of, as it is a fairly standard CC-R-C configuration with onboard rectifiers and space for three 35mm snap-in capacitors per rail. On typical class A voltages that means you’ll be able to use capacitors in the 22-33mF range and the the onboard rectifiers are 15-25A plastic SIP types, which should be just fine for most applications.

Input and output connections are via FAST-ON tabs and there are two sets of output connections. Since we’re paying for the copper on the boards anyway, I’ve tried to keep as much of it as possible  with a top-side ground plane and the supply rails on the bottom. 🙂

How big are the boards?
The board measures 3.1” x 6.675” (app. 78 x 170 mm).

What is the status of the boards?
Since the prototypes worked fine I haven’t made any changes and the board is therefore version 1.0.

Does it use any special/expensive/hard-to-find parts?
Nothing worth worrying about really. The only possible exception is only really the rectifier which is in a small GBU-package. However, Mouser has them up to 25A (p/n 750-GBU2510-G) and they are available from many other sources in 10-15A variants as well.

Anything else I need to know?

  • If you want to use off-board bridges, bridge the AC and the DC-connections with as thick a wire as you can get through the holes. That should allow you to use offboard metal-cased rectifiers up to 50A. Since the average current draw of most class A amps is quite low and the surge ratings aren’t that different between package types I don’t see the need to use anything else than the plastic ones, but by all means complicate matters with offboard bridges if you must 😀
  • The four series resistors can be 3-5W types in parallel which should be plenty, even if you want to burn off a bit of voltage in them.
  • The (optional) 3W bleeder resistor discharges the two first capacitors while the LEDs will discharge the last ones. The series resistor for the LED can be a 1/2W or 1W type.
  • Last, but not least: Electrolytic capacitors in this sort of size aren’t to be trifled with, so make sure you mount them correctly and test the board properly before mounting it in your amplifier chassis.

Downloads:
Download design files here

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

vfetpsupcb-2

VFET progress…

Well, not that much progress on the Pass VFET boards themselves – hopefully this weekend something will happen – but I have managed to make a PSU-board for them. Plenty of those around already of course, but being a) particular about dimensions and b) a bit particular about PCB colour matching I decided to roll my own instead 🙂

The design is a pi-filtered CC-R-C type with space for 35mm electrolytics, which at the VFET-voltage are available up to 27-33mF. As I plan to use the boards in mono-mode (one per channel) that’s actually enough energy storage to be a bit frightening. The Pi-resistors can dissipate up to 12W per channel which should be plenty (at least I don’t plan to go that high).

Also included are a polyester decoupling cap, a bleeder resistor for the two first electrolytics and a pair of LEDs which, apart from indicating power, also bleeds the last pair of caps.

As the pictures show, I’m still missing some parts but this project was never going to be a rush-job anyway so that’s just fine. The days in Scandinavia are getting noticeably shorter now, so saving projects for winter will not be a problem 🙂