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.

New AKGs are in…

It’s been a while since I last added to my already sizeable (and frankly unnecessary) collection of headphones, but now was the time.

Although new models come on the market regularly, the one “top of the line” model that I really wanted to get was the AKG K812. Up until a few months ago they have been very expensive and were only sold at RRP, but as they have started appearing at discounted prices I’ve renewed my interest. Although I’ve been eyeing them for a while now, it wasn’t until last week the stars finally aligned (or at least the combination of bank balance and foreign exchange rates🙂 ) and I could finally press the “buy” button.

When it came on the market some of the first reviews of the K812 mentioned harsh treble, but on the few occasions I’ve demoed them it didn’t sound particularly harsh to me. To be on the safe side I’ve bought one of the later-model “Made in Slovakia” ones, mainly on an assumption that any treble issues might have been teething problems in the first production runs of the original “Made in Austria” series.

I’m quite a big fan of the AKG house sound – and I have been since I first bought the K501 model when it was “flavour of the month” on head-fi a little over 15 years ago (yes, time flies…). I also own the K701, K550, K495NC and a few others and just as I expected my initial impressions of the K812 are that they are “more of the same” but better. As is the case with most other large AKG models (at least for me) the K812s are very, very comfortable once properly adjusted and I think I can wear them for a long time before they start being uncomfotable. For someone who wears glasses, this is definitely not a given when you buy a high-end headphone.

Obviously this purchase impacts the audio-related budget for my next big trip (in a couple of weeks) a little bit, but that’s ok – I’m sure it’ll be worth it once I get to spend a bit more time with these new AKGs😀

k812

More ATtiny experiments…

Since I managed to breathe life into my ATtiny-based speaker delay project I’ve been working on more ATtiny-based boards. There are many potential applications I can see (if I look hard enough…) for a small SW-based controller and that is what I’ve tried to build. The hardware was done a while ago, but the software was lagging (and still is somewhat).

I also received my TinyLoadr programmer a few weeks ago and it was definitely worth the wait. I’ve mounted the board to a piece of aluminium to keep it stable and now its more or less a perfect tool – very highly recommended if you want to play with ATtinys!!

To speed up my development cycle I’ve build a prototyping setup with a ZIF-socket and a solderless breadboard. I’m not a fan of solderless breadboards in general, but they do have their occasional uses and this would be one of them. I bought a few small ZIF-sockets from ebay and together with the tinyloadr programmer they make up an excellent prototyping platform. Swapping ICs from one ZIF to the other is still a bit of an annoyance, but it’s far more flexible than the alternative🙂

If you need more memory space (or more I/O-pins) than the ATTinys can provide then I am also working on an update of my AmpDuino-concept. This will be a fully-fledged controller based on a stand-alone ATmega-chip that can do the same as the old version AmpDuino, but in a more optimised way. Connections etc. will be laid out for what I consider to be typical audio applications. ETA is, as always when there is software involved, unknown😀

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 :-)

Project files: THAT1646 in stereo…

What is it?
A stereo version of my THAT1646 balanced converter/preamp shown here. I wanted to build a small controller/pre for some active monitors and while the stacked mono boards were probably a good idea in princple, I decided to resurrect the stereo layout instead🙂

How big are the boards?
The board measure 2.7″ x 1.9″ (app. 69 x 48 mm.).

What is the status of the boards?
There are two board versions which differ only slightly. One is 100% through-hole and basically a stereo version of the mono-board shown earlier. The other has the R4 gain resistor replaced with a 1206 SMD type and mounted on the top of the board (under the IC socket). This means the feedback loop area is much smaller and the routing is a bit neater. Both boards are otherwise the same size and electrically identical. If you want to change the gain after building the through-hole version is probably easier to work with, but otherwise the SMD-version should be the best design. Both boards are labelled as version 1.0 although I’ve only prototyped the SMD-version in stereo.

Does it use any special/expensive/hard-to-find parts?
As usual, not much. Maybe the THAT IC itself. Mouser has it though, so that should work for most people I guess.

Anything else I need to know?
A few things:

  • Gain: You can tweak the gain of the circuit as you wish using the resistors for the pampas, but remember that the THAT1646 should add 6dB gain on its own when you go from SE to BAL.
  • Opamp selection: You should be able to use pretty much any single opamp here. if you don’t have a favourite already I’d once again recommend that you start with either the OPA134 or the LME49710 and then experiment from there.
  • SMD resistor: If you are using the board version with the SMD gain resistor, remember to solder R4 on the board before you fit the IC sockets (otherwise some swearing may ensue when you discover it… :D)
  • BW limiting capacitors: There is no space on the board for BW-limiting capacitors for the opamp. Not sure why really, but with the opamp only driving a very short trace with a fixed load at the end (the THAT1646) I felt quite sure most opamps will behave. If not, soldering some small ceramics on the bottom of the board should be easy🙂

Downloads:
Download design files here

Related information:
As usual, RTFD! (= read the f’ing datasheets :D)

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

Project files: ATtiny-based power delay

As the PCBs for my next ATtiny-based designs have landed over the weekend and I am back from my holidays, now seems to be an appropriate time to post this🙂

What is it?
It’s my ATtiny85-based power delay controller which can be used for speaker protection etc. as described here. In addition to the controller board itself are also a couple of relay boards to do the actual signal switching. One board is stereo and based on 10A relays, the other is mono and based on a 30A relay.

The controller board includes an on-board 5V regulator, an LED coupled directly to the ATtiny to indicate when the relay is engaged (or another purpose) and two FET-switched outputs. The last two ATtiny I/O pins can be used to trigger the chip with buttons, sensors etc. which gives tremendous versatility.

How big are the boards?
All three boards are my “industry-standard” 2”x2” (app. 51 x 51 mm.) in size, meaning they can be stacked on top of each other if needed.

What is the status of the boards?
All three boards are version 1.0 and the prototype boards looked and worked as expected.

Does it use any special/expensive/hard-to-find parts?
Nothing serious this time either🙂

  • The small heat sink for the regulator is a Fischer type SK95 with an M3 hole in the bottom, but if you’re having trouble finding this there should be plenty of other small heat sinks that will fit. In any case, the heat sink isn’t always required, it depends on your input voltage and current draw from the 5V line.
  • The relays are standard types, either Omron G5LE (small board) or Omron G8P (large board). I’ve quoted Omron part numbers to give you something to go on, but there should be plenty of identical replacements from other manufacturers available.

Anything else I need to know?

  • The intention is that the ATtiny chip should be programmed using the Arduino IDE. That means you need to have either a dedicated programming shield for ATtinys or wire up the chip to an Arduino board that is used as an ISP. You also need to have the ATtiny cores installed in your Arduino IDE (see explanation here) and you have to burn the Arduino bootloader onto the ATtiny yourself before filling it with the actual program.
  • For programming, I highly recommend something with a ZIF-socket because it will make the whole thing much easier. I’ve got one of these on order (which recently came back in stock) because that looks brilliant, but there are shields on ebay that can be used as well. I’ve been working with this one so far and it works well, but of course you need a dedicated Arduino board to run it.
  • As you can see from the schematic, the intention is that the controller board is fed from a higher voltage (9-24V) than the ATTiny requires, in order to be able to use relays that draw less current. The onboard regulator will provide the 5V that the ATtiny requires.  If you are using the big mono relay boards, be aware that the worst-case power draw for these is around 1.2W each. This means that if you are using a pair of 9-12V relays here you’ll need to be sure that your power supply can handle that.
  • The second output is intended as just that – a secondary switch – but since it’s connected to one of the ATtiny pins that provide a PWM-output, you could probably do something clever and use this for controlling a variable-speed fan fed from the same voltage as the relays. If anyone does that I would love to steal, ehm…. borrow your code😀
  • Although the relay boards have on-board protection diodes across the coils, there is also space for optional SMD diodes on the bottom of the controller PCB. Use these if you’re driving off-board relays etc.
  • There is a sample sketch included in the download file, but please don’t laugh (too loudly) at my pitiful attempts to code – it’s just an example🙂

Downloads:
Download design files here

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

Most of the complexity here is around the coding. There are tons of links available around the web for how to use ATtinys with Arduino, so I’ll not list them here. Start from the link to the official Arduino page and then do your own search from there.