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 🙂

LED-tester deluxe…

A few months ago I stumbled upon a presentation thread for an “LED-tester” circuit by Muffsy-creator H. Skrodahl on a Norwegian audio forum. Two things immediately occured to me:

1) I want one!
2) I think I can improve this a bit 😀

So rather than simply downloading his posted Eagle files and ordering boards from there, I started doing my own board instead. With the final result arriving earlier this week it’s time to put it to the test.

The basic idea is to use an LM317 regulator as a variable Constant Current Source (CCS) to test unidentified LEDs and confirm what currents are required for acceptable brightness – something that isn’t always easy to guess based on the published specs. I’ve kept the basic circuit intact but my modifications basically consist of:

– “Real” connectors for all connections instead of just solderpads.
– Additional outputs for LED connections to allow direct plugging in, permanent wired connections and also temporary connections via test leads/crocodiles clips.
– Space for a stereo pot to give a bit more mechanical stability.
– Optional “high-current” mode for testing constant-current LED bulbs as a supplement to just normal LEDs.
– Four real mounting holes to allow the board to be fixed to a bit of scrap metal or similar for use in a lab environment.

I need to do a bit more validation on the prototype before I publish my board files, but at least I can confirm that it works and that it is a very useful way to identify the operating parameters of e.g. LEDs in pushbutton switches.

Project files: The last of its kind…

…for a while at least 😀

What is it?
The last (and smallest) version of my EL2k buffered headphone amp using NOS Elantec 2008/2009 buffer ICs. This is the smallest version designed for 1.5″ heat sink profiles as described here. The two other versions are of course also still available (here and here):

How big are the boards?
The board measures 3.95″ x 1.5″ (app. 100 x 38 mm.) and is obviously a mono amplifier channel.

What is the status of the boards?
I’ve called this board version 1.5 as it is a redesign. Apart from the redesign work described in a previous post, the circuit is identical to the other published files.

Does it use any special/expensive/hard-to-find parts?
Yes.

  • The EL2008/EL2009 buffers have been out of production for 10+ years. They can still be found and I don’t think you need to be especially concerned about fakes – there can’t be a lot of demand for these anymore – but of course no guarantees. The main risk is probably that instead of NOS parts that you get used parts that have been pulled from old equipment. This is annoying, but should be OK.
  • The heat sink profile is the same as the original, Fischer SK68, in 37mm length. Easy to get in Europe, but I’m not sure about elsewhere.

Anything else I need to know?

  • I’ve had to mount the buffers on the side of the heat sink that has an M2.5 slot and not an M3-slot. This isn’t a problem as such because there’s no need to isolate the tab, you’ll have to remember to buy M2.5 screws for mounting 😀
  • Otherwise this is a bog-standard buffered opamp circuit and there isn’t much that can go wrong 🙂

Downloads:
Download design files here

Related information:
Be sure to read the original posts for additional information and tips.

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

Switched on?

Another project that’s been on hold for a very long time because I did not really need to finish it….

It’s a balanced two-in/two-out passive switch box which I intend to use partly to add an additional input to a spare amp, and partly to build a more comprehensive test setup for comparisons of sources and amps.

The signal switching is done via relays (see here for original post – oh how time flies!) and the power supply for the relays is an IRM power supply module as showed a few weeks ago. Switching of relays is done with latching button switches that I still need to wire up once the front panel is drilled and that’s about it really 😀

The relays are transistor controlled and 5V types, so while it is simple for now there is plenty of scope for adding functionality via an Arduino/ATtiny-based controller of some sort. The most obvious feature would be an IR remote control, but another thing I was originally thinking would be to add ABX-logic to try some blind testing. I sort of gave up on figuring that out, but if anyone knows how to build this in Arduino code give me a shout 🙂

Zero Audio?

Around a year ago I first tried making a music streamer from my original Raspberry Pi, a digital converter board from Audiophonics and Volumio. Apart from my unfamiliarity with Linux causing some confusion, it actually worked well and it caused me to have a bit of a mindset change. Originally I wanted to have my music stored locally on a harddrive on the playing device (a MacMini with Amarra), but since the NAS I use for redundant backup of files is just sitting there anyway, streaming was suddenly a viable option. Since then I have been happily using a RPi 3 and cheap digital converter board from ebay as a streamer to feed my Arcam DAC, switching between Volumio and Runeaudio for the software-part.

I am mostly happy with this setup, but since the RPi Zero came out a while ago I’d wanted to try using that for something similar and take advantage of the compact size. To match the Zero I bought a “TinyToslink” adapter to give the Zero an optical output to feed my DAC. It seems to work well, but it’s a bit surprising – in a good way – that something less than half the size of a credit card (excluding all the necessary adapters of course 😀 ) produces sound like this.

I have some ideas for how to case this to make it pretty, but it’s going to take a while as it’s not a priority right now. Also, the TinyTOSlink is not as sophisticated as e.g. the Hifiberry Digi+ Pro (which I have my eye on as well), and there are a few things that could be better. One of the problems is that it doesn’t do 192 kHz over optical (and my DAC will not accept that either), so I have been wondering about DIY’ing a version with transformer-isolated coax out instead – maybe later ;).

I’ll probably continue experimenting a little with the Zero and leave the RPi3 in my main system, but if you want to get a cheap streamer together the Pi – regardless of format – is a good option. And it can of course also do many other things as well (especially if you can be bothered to learn some basic Linux, which I can’t right now 😀 )

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.

Class D experiments…

There are many class D technologies on the market at the moment, but one of the ones I haven’t tried (until now at least) is the International Rectifier “IRAUD7”-amps (IRF has been acquired by Infinion).

Consisting of the IRS2092 driver IC and various purpose-built FETs (many of them two FETs in a single package suitable for half-bridge designs), this is by most accounts a good-sounding and scalable class D technology. It’s also one of the few technologies where you can actually have a go at your own PCB layout if you want to. The schematics are available in IRFs published reference designs (here and here) and although making good PCB layouts for high-power switching electronics isn’t easy, it is actually possible to do.

Of course, when something is so easily available it tends to get exploited. It wasn’t long after IR introduced the designs before the market was flooded with several cheap clones, some using their own PCB layouts and some using IRs own Gerber files which are also published on the website. I had my eyes on some small (credit-card sized) boards to try for a while as they were really cheap (do an ebay-search for “IRS2092” and you’ll see 🙂 ), but eventually spotted this “luxury” version (at least based on appearance and observed parts quality) and fell in.

This build is the “low power” version with the IRFI4019 FET, but there’s also higher-power version with the IRFI4020 FET. Since the seller I bought from made a mix-up in ordering I actually ended up having a pair of each version, but I wanted to start with the low-power version. Then I might go dual-mono on the high-power boards later on if the sound quality proves it worthwhile 😀

The PSU consists of a 200VA transformer and a cheap supply PCB with 45mF capacitance per rail – mostly because that was what I had in my parts drawers. I’ve tried to keep the mechanics as simple as possible since I consider this build an experiment, but having the amp and PSU on a mounting plate simply makes everything much easier so I decided to “splurge” a little anyway :). The front panel is blank until I decide how the amp is going to be used.

Even though the pictures show the amplifiers uncabled (which they still are), I did manage some sneak listening on the modules and I am looking forward getting these into my main system for a proper test 🙂

 

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

Happy New Year!

Yes, another year has gone and so up comes another opportunity to reflect on the status of the blog 🙂

Well, sort of anyway. I would like to have said that I am writing this on New Years Day from my desk in the middle of a build, but I’ve actually decided to write this in advance, let WordPress handle the logistics of posting and then bugger off to Italy for New Year’s instead 😀

This (well, last) year I feel I have been a little bit more limited in terms of time to post, but I still have plenty of projects in the pipeline, plenty of ideas I want to realise, plenty of experiments to be done etc. Heck, even the bank balance looks in reasonably good shape 😀

The only things generally lacking are time (not much I can do about that unfortunately) and then space for the projects that I finish (I might be able to do something about during the coming year, who knows?). Overall though, I think there’ll be plenty of stuff to write about during 2017 as well.

I’m still excited to see that both visitor numbers and views are steadily increasing and I think that I manage to keep the signal/noise ratio quite high here – I hope you agree!

All the best to everyone reading and best wishes for 2017 🙂

Gold glitter Happy New Year 2017 background. Happy new year glittering texture. Gold sparkles with frame. Chic glittering invitation template for new year eve.