More finished stuff!

Although there is a tiny bit of light at the end of the Covid-19 lockdown-tunnel (at least in my part of the world), the “new normal” (or at least “interim-normal”) of working from home and attending lots of online meetings still continues. This means I also continue to have more time than usual for building, so I’ve managed to complete a few more projects over the last week or so. I know it might not seem that much, but compared to my usual rate of progress it’s starting to feel like an assembly line! 🙂

First up is the AD1865-based DAC I showed here. It works as intended and sounds fine, but honestly I need to redo the wiring because it’s not really optimal. Not now though 🙂

Next is my 50ASXBTL-based amp. This is the original “prototype” I did of the SE-BTL conversion for the ICEpower 50ASX modules and while there have been some reports on diyaudio that the conversion isn’t as straightforward as I made it seem, I can confirm that at least based on sound the finished product still works well.
However, the last strech of this build wasn’t without issues, firstly because I had to redo the bottom plate as I realised that glass fuses on the primary side of an SMPS is not only a bit stupid, but also not necessary when each PSU is already fused on the board. Secondly, that turned out to be the easy part because I did most of the wiring by memory which in hindsight wasn’t the best choice. Anyway, after a few more attempts than I expected (and after swearing at everyone and everything including my own stupidity) it actually works well now – nice!

Last, but definitely not least, is the basic ICEpower700AS2-based power amp I showed here. This deserves a new 10mm custom front panel at some point, but it plays well and for now I think getting some more listening impressions is higher on the agenda. My initial impression is that this could well be my all-time favourite ICEpower-amp, but let’s see how it goes when I put a few more hours on it.

Hopefully this week will bring a new batch of front panels (or actually, rear panels) so I expect to be able to keep up the current level of progress a little while longer 🙂

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 😀

An ICEpower 50ASX amp – the easy way…

Some weeks ago a reader on the blog asked me some questions about various pre-made options for putting together a simple amplifier based on the ICEpower 50ASX2 module.

One of the options mentioned was to buy a case-kit for the module from Ghent Audio in China. I’ve seen pictures of these cases before and not only do they look quite good, they also come pre-drilled and silkscreened which for most DIY’ers is the hardest part of building stuff. I answered the questions as best I could without any hands-on experience to offer, but as I had an older black 50ASX-module left over I decided afterwards to get a case for myself and try them out.

After the usual waiting on shipping (which wasn’t actually that bad – app. 2.5 weeks), the case kit arrived. Everything is included, a power switch assembly, AC inlet, terminals etc and it seems to be decent quality all round. I didn’t buy the full cable kit, which would have made it even easier to assemble, but still it’s not too bad.

Putting together the basic kit with the module, feet, switch etc. ready for cabling only took around half an hour or so. If you look at the pictures I’ve made a few “adjustments” to the kit by using stainless screws and feet (the kit comes with black screws and matte silver feet), but otherwise it is as delivered and of course using the original parts would also have been just fine. The terminals are decent quality, but not the best I’ve seen. Also, the terminal holes are drilled too large (presumably to accommodate changing suppliers) which is slightly annoying but by no means a deal-breaker.

A bit more digging in the parts drawers revealed some suitable pre-made cables for signal and speakers – and a problem: my stock of JST connectors for the power connections has run out (or run away :-))

So yes, in conclusion this is definitely an easy way to build an amplifier (just as long as you ensure you get all the parts before you start 😉

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 😉

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 🙂

Surrounded – again!

This is an old project that I have resurrected now as I would like to get my surround-sound setup back into working order (not that I expect I’ll be using it that much, but still…)

It’s a 2+3 channel ICEpower ASX-based setup with 125ASXs in BTL-mode at the front and 50ASXBTLs for center and rear. The 2-channel amplifier very nearly identical to my previous 125ASX-based amplifier but it does have three USPs compared to that build:

• Transformer-coupled (balanced) inputs using Lundahl LL1527 transformers.
• Two switchable inputs so it can be connected to both a stereo source and a surround-processor simultaneously.
• ”Audiophile” form factor (i.e. around 44 cm. wide and much larger than is really necessary 😀 )

The 3-channel amplifier also has Lundahls at the input but no input switching (for obvious reasons).

Many upmarket manufacturers use transformers on the inputs of ICEpower-based amps and Lundahl in Sweden make some of the best ones around. The LL1527 isn’t usually employed as an input transformer, but if I’m reading the specs correctly it’s actually fairly well-suited to the lowish input impedance of the ICEpower modules so it should work well. The alternative (which would also fit on my boards) is the LL1540 which is a purpose-built high impedance input transformer. And well, if all else fails the way that these are mounted would mean that I could probably develop an active circuit instead 🙂 (differential opamp-board anyone?)

Just like my as-yet-not-completed “Ring” amp project the front channel amp has switchable inputs so that it can be used in a combined stereo/surround setup. Switching after the respective volume controls make more sense to me, but of course I haven’t actually lived with it yet so let’s see if theory meets practice in this case 😀 This switching is relay-based and uses the balanced selector modules I posted about earlier – yes, sometimes those piles of leftover prototype PCBs come in very handy :D.

There isn’t actually a lot missing – mostly cabling – before this is done, but I hate cabling so it might take a while to do it anyway 😉

Waiter, more ICE please!

After building the 6-channel amp with the ICEpower50ASX modules my stock of modules still wasn’t depleted. Time to fire up the imagination then…except not a lot of imagination was needed to come up with this to be honest 🙂 It’s a very simple miniature poweramp in a small Modushop enclosure (cabinet dimensions excl. terminals, feet and front panel is around 130x175x40mm).

The main point of this build is small size but of course that makes the layout fairly cramped. The amp works fine as it is, but there are a couple of issues which I plan to rectify in an upcoming “v2”. Firstly, the mains switch is a bit small, in fact so small that the inrush current from the switching supply causes it to “stick” quite badly. Secondly, I have reversed the position of the left and right outputs compared to what you normally see. While it makes for slightly neater wiring on the inside, it makes for ridiculously impractical wiring on the outside (trying to cross a pair of stiff speaker cables) so that has to go as well.

Soundwise, this is quite good. From my recollection, the 50ASX is the “warmest” sounding of the ICEpower modules which is quite nice, and there is enough power on tap here (app. 50W into 4 ohms) to supply my speakers at normal listening levels. I have a matching Pass Preamp in the works as well, and with those two I actually think that is all anyone really needs from a sound system (not that this will stop me from building more gear obviously :D)

Past projects: 6-channel ICEpower50ASX amp

In have owned a number of ICEpower-based amps in my time, partly because I think they are great amps that offer great ease of use and a lot of value for the money – and partly because I used to work for the company 😀

My 6-channel amp for surround sound is based on three stereo 50ASX modules. Where the “older” ICEpower modules in the A- ASC- and ASP-series were build entirely with “off-the-shelf” parts, except the magnetics, the ASX series modules are built around a proprietary ICEpower controller and driver ASIC chipset. This means the performance is better and the modules can be mechanically smaller.

The 50ASX is the smallest of the range and as the pictures show, these modules are very compact. Two amplifier channels including the switching power supply takes up only 8×11 cm of PCB space (around the same size  as two credit cards placed side-by-side). Power output is a fairly modest 25W/8R and 45W/4R, but the amp bridges to around 170W so the power supply is quite powerful and for normal listening conditions these have more power than you’d think (note that the SE-version doesn’t bridge, while identical in build, the 50ASX modules are hardwire for either SE or BTL operation from the factory).

A commonly cited “problem” with the ICEpower modules is the low-ish 8kOhm (or so) input impedance. Because of that (and because I wanted to try it) I added some input buffers. These are based on the LME49710 opamp with +2 gain and a 51kOhm input impedance.

Soundwise, for a smallish listening room with relatively efficient speakers this is very good. The 50ASX modules are great little amps that sound very open and spacious over the whole frequency range – and surprisingly powerful at the low end as well. The compact size is definitely a plus as well, the 1U enclosure with feet is actually overall around the same size as my surround front-end, an Audiolab 8000AP processor.

I haven’t done very detailed comparisons between the 50ASX amp and its bigger brother, the 125ASX, which I have also used before (here and here). My initial impressions though is that the 125ASX is more neutral while the 50ASX has a slightly warmer character, but since the 50ASX’es in this configuration is buffered while the 125ASXs are only stock, I am not 100% sure of this. I’ll have to do some more “scientific” comparisons one day 🙂

Anyway, I have a few more of the 50ASX modules in the drawer (including some of the BTL-version) so obviously there are a couple of more projects in the works – stay tuned 🙂