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.

Project files: The (modified) EL2k headamp

What is it?
The board files for the new “medium-sized” version of the EL2k buffer/pre as shown a few weeks ago. The smaller 37mm board version will follow in a while.

How big are the boards?
The board measures 3.95″ x 2.0″ (app. 100 x 51 mm.) and is obviously a mono amplifier channel.

What is the status of the boards?
I’ve called this board version 1.5. Apart from the redesign work described in the last post, the circuit is identical to the originally published v1.1 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 50mm 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, but some swearing will likely ensue when you sit there on Sunday afternoon and realise you don’t have any M2.5 screws to hand 😀
  • 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. You should be able to reuse the linked BoM as well.

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

50ASX BTL conversion (part 2)…

So, I’ve done some more testing on my BTL-converted 50ASX-modules…

As you can see, I’ve used a slightly less improvised test setup compared to last time (it looks worse than it is…). While I wouldn’t call what I have done “extensive testing” by any means, my gut feeling is that this works 🙂 It also ties in well with how the other ASX-modules work and some “insider knowledge” from years ago that I can still recall 🙂

Note and disclaimer: I would very much appreciate if someone else tried this to verify and maybe do more testing, however I will accept no responsibility for damage to property, people or pets (or anything else for that matter) if you find a problem – this is DIY after all 😀

You can of course hack this conversion anyway you like, but I opted for removing the old jumper altogether and soldering in a new one. If you do that, be advised that the ASX-board is four layers and soldered with lead-free solder, so it will take a bit more heat to reflow the joints than I am at least used to. If you use a soldering iron that is too small, you’ll just heat up the board and possibly damage it.

My suggested approach would be to cut the jumper on the top side of the board. Heat the solder joint from the bottom and pull out the jumper wire with small pliers. Then clean the remaining solder off the board with desoldering braid or (better yet) a vacuum desoldering station if you have access to one. Then solder in the new jumper in the BTL position. There isn’t much space to work on and you should be careful not to damage any of the (sometimes annoyingly) small SMD-components on either side of the board. Once the new jumper is in place, follow the wiring diagram for the BTL-version in the 50ASX data sheet/designer’s manual and you should be good to go.

Bear in mind that what you end up with isn’t a “real” balanced (= differential) amplifier, but two SE amps referenced to ground and driven with opposite phase input signals to produced a bridged output. As such, the input ground is still required in order for the amp to produce a correct signal on the output. I’ve found a good sketch here for LM3886 modules that should show the correct input wiring. Output on the ASX is taken from the P104 connector, so ignore what the sketch shows here (and of course the DC wiring is irrelevant as well).

If you do try this, let me know how you get on 😀

PS: Yeah and the picture is still crap – but don’t worry, the light should be better from around April onwards 😉

50asxbtltest-1

ICEpower 50ASX – SE to BTL conversion

I’ve recieved a few questions (and participated in a diyaudio discussion thread) about converting ICEpower 50ASX2 SE modules (which are fairly easy to get), into 50ASX BTL modules (which aren’t). I was pretty sure this could be done without component substitutions by simply desoldering the W401 jumper and resoldering it into the W400 position (marked BTL on the bottom of the board) but as I had no modules left, I couldn’t try it. Now I’ve managed to get my hands on some more modules and I’ve actually tried converting one of them and the good news are – I think it works!

I haven’t actually measured anything (not sure what to measure to be honest) but I get clean audio out on the BTL speaker connector (P104) and a very loud buzzing noise on the other output, so at least it isn’t running stereo anymore. No guarantees on anything yet though, but it’s definitely promising.

Oh, and don’t laugh at my improvised test setup, it is necessary because I don’t have a proper balanced source in the house at the moment and I couldn’t be bothered to crimp new cables just for testing 🙂 Incidentally, don’t laugh at the poor picture either – winter in Scandinavia means the days are so short that I can only take pictures in daylight during the weekend…

Next up is to convert a second module, build some better cables and try it “for real” in a stereo setup – hopefully this weekend 🙂

50asxbtl-1

Evolution of a design…

Sometimes when looking at a design I was originally quite happy with new ideas come up and I start to rework the design, either as an optimisation of the original or simply as a “branch” that I hadn’t originally considered.

One such example is my “EL2k” buffer/preamp/headamp design. I was fairly happy with the original layout, but when I contemplated putting four boards in the same box for a balanced configuration the original board size started to look a bit big and so a redesign-attempt was in order.

Originally the ambition was a “space no object” design which had room for the best quality parts possible, but aside from that the original design goals were simple:

  • Through hole parts where possible
  • Short signal path and good decoupling as per the component datasheets
  • “Overkill” Fischer SK68 heat sink profile because I like the way it looks and because it provides solid mechanical mounting to the board.

Mostly because the heat sink profile comes in predefined sizes (which means that there are some natural steps in how the board should be shrunk), I thought this could be an interesting way to showcase the evolutionary process of what I ended up with 🙂

On the original version I was pretty happy with the basic layout and most of the traces are as short and as clean as the physical layout allows (at least I think so…). The only real exception is the unsightly top layer trace that links the negative supply to the buffer with the negative supply pin on the opamp. The first step was to try and tackle that….

el2k-evo-1

…and it’s not easy. There isn’t really a lot of space to begin with, and even with tricks such as physical jumpers and SMD decoupling caps I wound up more or less back where I started (see below).

Next came trying to actually reduce the board size. The next step down in heat sink size is 50mm, so that becomes the target. End result:

el2k-evo-2

The 50mm version actually looks good to me and there are very few actual compromises here.

  • The input cap has been moved and it has been changed to a 27.5mm lead spacing box cap (with a 15mm option). It’s a small step down in quality vs. the axial cap on the original board, but probably still fine for most people/applications.
  • The power LED arrangement has been changed. The original “1 LED per rail” replaced with a single LED connected between the supply rails. In return, the LED resistor was changed to a slightly bigger package that allows for resistors up to 1W.

Now, the next step down in heat sink size is 37.5mm.

el2k-evo-3

Now we’re seeing some actual compromises 🙂

  • The basic layout is still the same, but the input cap has been shrunk considerably to a 15mm type. However, that in itself is not enough and one of the mounting holes had to be removed to provide space for the input connector.
  • The output connector also had to be removed and replaced with solderpads.

Other than that, it’s pretty much identical to the 50mm version. This led to a bit of thinking – what if the input cap was removed altogether? – and either omitted or mounted off-board? That would allow the fourth mounting hole to be kept. However, since the cap can easily be bridged and the board still has two mounting holes on the “heavy” end, this was deemed unnecessary overall.

el2k-evo-4

Both of these versions have larger compromises as far as I am concerned, but still not unacceptable if I had an application that required the smaller PCB size. Suddenly it becomes possible to take the idea of a balanced-bridge amp and realise it in almost the same space as the original stereo amp. Also, it gives an excuse ahem, opportunity, to design a backplane for the amp boards to keep the wiring tidy and make it look better 😀

It also becomes clear that it isn’t really possible to shrink the design further without making substantial changes. A stereo board version would of course be possible, but looking at the configuration of parts around the EL200x IC and it became clear that I couldn’t have two amplifier blocks side-by-side and keep the original arrangement of power supply, decoupling, signal routing etc. Also, when deciding between a stereo 75mm version and a mono 37mm version, I would normally choose the latter as it is cheaper to manufacture and more versatile in use.

So, all things considered the original 75mm version is still good but the “modified” 50mm version should be almost as good. The 37mm version doesn’t give up the overall flavour of the original design and it’s definitely still viable, although the exact application would have to decide exactly which compromises to make. Not bad if I do say so myself 🙂

So with that done – expect to see revised prototypes in about a month or so 😀

Paypal grumble…

Slightly off-topic post, sorry. Like most people that shop online (especially on Ebay and from private sellers on discussion forums) I use Paypal extensively. Normally it’s relatively easy, safe and convenient. However, earlier this week I started getting error messages that the two debit/credit cards I have linked to my account were no longer usable as payment. I managed to link a third card and complete the transaction, but I started wondering what was going on.

It turns out that Paypal at some point last week have made the default option for transactions the same currency that your credit card is issued in, even if there has for a long time been an option to set this per credit card you use. I’m sure that somewhere this is listed as a “customer service initiative” or “security initiative” (yeah!), but nevertheless it is one that just happen to give Paypal a further few percent commission on the exchange rate (I haven’t calculated it exactly but it looked like a 3-5% markup depending on the currency). This is of course unacceptable when I pay fees already (or the seller pays them, which means in the end I pay them).

Fortunately after some googling it turns out there still is a way to pay the actual transaction amount and let the card issue handle the conversion (which in my case they do with 1% commission on the official rate from the National bank). Before completing the purchase, click to change payment method and then click the exchange rate to change back to using the card issuers rate. I haven’t tried with a direct Paypal transaction (only via Ebay) but I will be keeping my eyes open in the future….

Oh and, needless to say I will from now on always avoid using Paypal if there is another payment option listed where I shop…

EDIT 29/11-16: Have now tried to send money via Paypal directly and here I can’t change the conversion option. Then I spotted this in the latest revision of the user agreement “Where your payment is funded by a Debit or Credit Card and involves a currency conversion, by entering into this agreement you consent to and authorise PayPal to convert the currency in place of your Credit or Debit card issuer.” Which basically means that they decide the exchange rate and if you don’t like it you can f*** off…

Anyone know of any good alternatives to those Paypal bas***ds?

Shopping in Japan (again…)

Yes, I’ve just returned from a two-week trip to Japan – my third in as many years. Apart from a load of sightseeing and general holiday’ing, just as the two previous trips (see here and here) I had a chance to do some shopping. Not the only reason for going, shopping in Japan is in my opinion an opportunity that shouldn’t be missed for any audio and electronics enthusiast 🙂

Although it is no doubt just a shadow of its former self in this respect, Tokyo’s Akihabara district (and it’s less well-known counterpart in Osaka, Nipponbashi or “Den-den”-town) are still interesting places for DIY’ers to walk around and browse. The pictures below are from a couple of the shops I’ve passed on my way and I’m sure you’ll agree it looks interesting 🙂 Finding adresses can be a bit tricky – and not everything in Japan is on the ground floor for all to see – but there are a few good resources available online on where to go, such as Pete Millet’s “Parts in Asia” page that covers Tokyo and various blog posts.

Is it cheaper than buying online? Not always to be honest, but it’s definitely much more fun! 😀

So, what can (or should) you buy in Japan then?

Well, if you are from Europe like me, most Japan-made items will be cheaper there. If you are in the US, the prices might not be all that competitive for everything but it’s still worth having a look around.

Apart from finished electronics that aren’t wall-powered (anything wall-powered is often 100V-only for the Japanese market and so not useable anywhere else), that means headphones and other gear from the likes of Stax, Audio-Technica and all the usual big-name brands like Sony, Pioneer, Denon and Onkyo. Smaller electrical items which use outboard power supplies may also work, provided you factor in the cost of replacing the PSU and of course accept that the warranty on Japanese items usually isn’t valid outside of Japan.

It also means cables and connectors from the likes of Canare, Mogami and Oyaide as well as a heap of excellent-quality tools. I’d especially recommend the Japanese “Engineer” brand where everything I’ve seen and tried seems to be excellent quality. There are several other interesting tool brands as well, but the stuff from Engineer seems to be consistently good and prices in Japan can be 30-50% lower than the EU prices I’ve seen (although the yen has climbed a fair bit against the Euro over the last year).

I also saw several places selling loose connectors of the most well-known series from Molex and JST. These can be hard to get as well, so being able to get singles just off the street might be helpful. There were a few shops with audio-grade parts like ICs, pots and capacitors and again, Japanese brands like Muse capacitors and Alps pots were generally cheaper. A bonus should be that these parts are probably less likely to be fakes than if you shop on ebay etc.

If you are into tubes, there are a few good places for both tubes and accessories such as transformers (see Pete Millets page for details). Don’t expect to find screaming bargains (although you might) and ignore at your own peril that tubes don’t necessarily travel well and transformers will tend to take a big chunk out of your airline luggage allowance 🙂

Oh, and of course regardless of whether your shopping allowance is more limited (or far greater) than mine, Japan is still a phenomenally interesting place that I highly recommend visiting if you get the chance 🙂

Minipre in a box…

A while ago I presented my “MiniPre”-project of a simple op-amp based preamplifier. Now I’ve had occasion to put it into use as a small standalone preamp/active monitor controller.

The design is very simple, so not much to be added there (whatever you need is probably already in the original post), but it’s basically a standard dual op-amp in non-inverting configuration.

The power supply will be in the form of a small DC-DC converter (a continuation of my previous experiments) so that I can feed the box from a single 5V supply and keep the case size down. Because of this I’ve managed to cram everything into the smallest available hifi2000 case, so it will fit nicely on a desk 🙂

The advantage of this simple design is the the selection of opamp tends to have a noticeable influence on the sound signature, so this is one place where there is room to experiment whether different options have better synergy than others.