A new king?

Normally I spend a surprisingly low amount of time listening to the builds I finish, but this one is an exception. That’s because I finished casing my Hypex NC502MP class D module and as I have very little experience with the Hypex class D amps, I had to try it out.

The original plan for the module was to build a top-end “integrated” amplifier but I quickly abandoned that idea (however, I picked it up again later with this build). Instead I’ve simply cased the module in a basic Modushop case but added an 8mm thick piece of aluminium to the bottom. A small niggle is that I can’t seem to find the crimps for the signal connectors so I used the cables I had to get the amp working, but it would be nice to be able to put in a functioning mute switch and a power LED as well.

As you probably already know class D is very efficient and class D amps therefore run very cool – right? Not quite actually. The very high efficiency numbers are always measured at (nearly) full power and at low power the efficiency is typically quite unspectacular. The Hypex module here has idle losses of around 20W, which honestly isn’t far off what you might get from an 80-100W class AB amp with a traditional power supply.

The module does therefore run quite hot and don’t for a moment think that my “thermal design” here is suitable for anything except a limited home use application. Even so, it’s hotter than I expected and what surprises me most is actually that I measure very high temperatures on places like the output chokes – these parts are not heat sinked to the backplate and so presumably a better heat sink on the back would not make much difference?. In any case the few experiments I did were enough to break with my conventions and order a ventilated lid for the amplifier instead of the usual one I use, because running the amp “topless” did make a difference to the temperature of the board.

On to the listening then: The logical comparison is against my “new favourite” ICEpower amp, the 700AS2. However, initially I just hooked up the Hypex amp to my test speakers (a pair of 5” Tang Band full range drivers in small reflex boxes) and even then it was obvious that this is a high quality amp. I especially noticed that the small TBs actually managed to sound like they had some bass articulation, which definitely isn’t common. In fact, the very improvised “test setup” ended up staying on my temporary work-from-home desk for three days of near-field listening.

Moving the amp into the main system and the positive impressions continue – this really is a great-sounding amplifier. To make a long story short though, I still ended up returning to the ICEpower amp in my current system for two main reasons: One is that the ICEpower amp seems to give a slightly wider soundstage which I am honestly a bit of a sucker for, and the other is that the ICEpower seems a little leaner in the bass. Whether that is a good thing or a bad thing in absolute terms I am not sure about, but my speakers are quite bass-heavy already and any more just makes them boomy which I don’t like.

Be in no doubt that to me this is a very capable amp though, and as I have a suitable enclosure with a bit more heat sinking that would suit a dual-mono setup I’ll definitely be keeping an eye out for a pair of the mono NC500MPs 🙂

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 🙂

A tweeter amp…

Another overdue board design that finally showed up recently is this one. I would not call this design one of my “heroes” (like the last post), but it’s probably one of the “most-revised” since this version is actually the third iteration (although I honestly haven’t ordered or built the previous two iterations – not entirely sure why…).

So why is it called a tweeter amp? Well, two reasons: One is that the original intention was to supplement a single-supply class D amp in a bi-amp (plate-amp) setup, especially the power take-off on an ICEpower 200ASC/300AS1-module. The other reason is that if you want to improve the sound quality within the limits of the small board you’ll get a low-end roll off that means the amp is not going to play a lot of bass at all, but for a dedicated tweeter amp it is still perfectly usable.

The circuit is simple – it’s basically my version of the bog-standard single-supply circuit of the LM3886 IC (or its cousins, the LM3876/LM2876). With the kind of power supply you normally have available (single 45-55VDC) you only get 20-30W output, but as a dedicated tweeter amp this goes a surprisingly long way (and even further if you use an active filter in front of it). I have to admit that this idea is not actually mine, but something I have seen a manufacturer of active PA-speakers do several years ago (exactly with the ICEpower200ASC module as the bass amp and PSU).

The board works as-is, but it’s got a bigger turn-on thump than I would like so I need to see if I can get that a bit lower somehow. Otherwise I seems workable as-is – and my first impressions of the sound quality are actually also very good. I don’t have any of the ICEpower-modules at the moment, but I’ve got some industrial switching PSUs that I want to try out as well to see if they work.

 

JISBOS/Alpha20 buffer clone…

I’ve got a few projects that are now very nearly finished and also a couple of new PCBs in the mail that I am pretty excited about, but before we get to any of that I just want to show a bit more about the buffer design that I presented in my last post about the integrated ICEpower amp.

The Alpha20 buffer by AMB was originally called the “JISBOS” because of its “JFET input stage, bipolar output stage” and its original design pages are still online here. Sourcing the JFET inputs are of course a constant problem, but fortunately I bought some with my original boards from AMB. The first version of the design was a pure buffer, but since then AMB added the option to have gain as well – not something I need right now, but definitely adds to the versatility of the design.

Technically there is of course nothing wrong with AMB’s original board layout, but a couple of things were annoying me. One is that the original board is intended for very small resistors which I would have to buy, instead of just being able to use the RN55s that I have already (yes, I know it is possible to make the RN55s fit a 7.5mm lead spacing, but for me it always ends up looking like crap and a real 10mm LS is much easier to work with anyway).

Another niggle is that power and I/O connections are just holes in the board. That makes it pretty easy to solder up a permanent design, but it is a royal PITA for testing and also in case something ever goes wrong. Last but not least, I really like having LEDs to give some indication that the board is powered and operational. Of course this is not bullet proof in any way, but as a quick indication that everything is OK I find it works well.

The original plan was to run these boards without heat sinks (because they are only for line-level applications and not supposed to deliver a lot of power) but at the last minute I chickened out and put some small heatsinks on anyway. I’ve actually got another layout version with the output transistors turned 90 degrees. Then there is space for heatsinks to extend over the sides of the board, which for headphone use and other high-power applications would probably be better.

Now as I wrote in the previous post I don’t normally set out to make my boards twice as large as the original, but in this case I am willing to take that tradeoff for the improvements I have made – so let’s hope the finished amp will sound as good as I expect it to! :).

Starting the 250ASX-int…

For a while I have been thinking about doing an “all-in-one” integrated amplifier and therefore I’ve been looking for a suitable class D amplifier module as the “centrepiece”. A few weeks ago the perfect candidate showed up in a local classifieds ad and so I picked up a single unused ICEpower250ASX2 module at a fair price. Conceptually this build is quite simple – two switched single-ended inputs and a buffered ICEpower module with a volume control inside. However, just doing that would have been a little bit boring, so I added a some complexity to make it interesting 🙂

Part of my reasoning to build this at all was that I wanted try out an ESP8266-based amplifier monitoring & control board I developed based on my IoT-T design. This control board was actually intended for ICEpower-modules so that I was lucky enough to pick up a 250ASX was really good. The original inspiration for the control board wasn’t even the ASX-modules but rather the Pascal-module which has the ability to output quite a lot of monitoring and diagnostics signals. However, as I only have one Pascal module and no reliable way to get more I decided to build a first version to suit the ICEpower ASX modules instead.

I don’t really have working software yet, but when completed the finished amplifier should have the option of basic web control and monitoring via the ESP’s Wifi connection as well as driving a “local” front panel LCD display via I2C. I haven’t fully decided if I want to use this feature for this particular build, but at least the option is there. A potential problem is that the ESP8266 is going to be enclosed in a aluminium and steel box and the Wifi-connction might not like that. Obvious solution #1 is to use a ESP pro module that can be fitted with an external antenna on the back but my mechanical layout is suboptimal for this purpose to say the least. Obvious solution #2 is to ditch the steel lid in favour of acrylic or something else – we’ll see where I end up with that.

Another goal of this design was to try using a discrete buffer such as the JISBOS/Alpha20 with the ICEpower amp as I’ve never really done that. However, once I started looking at the A20 boards from AMB that I already have I decided I preferred to do my own version instead. Normally my goal with clones is to make stuff smaller but in this case I ended up making it about twice as large as the original… Still, I think it was worthwhile to do and I’ll probably do a separate writeup on this design later. For input selection I have a basic design that works (I only need two inputs), but once I got the boards I have out of storage I couldn’t resist messing with them a little, so I can’t finalise this until the new boards show up (which may take a while if all the factories in China stay closed due to Corona-virus…)

For volume control I ended up with a very difficult requirement, namely that it had to be controllable by I2C from the control board. That’s a surprisingly difficult one since the “usual suspects” for high-quality audio (e.g. a PGA23xx or similar chip) requires SPI, so my solution ended up being something else – we’ll see if that works 🙂

A new flavour…

I finally managed to get an opportunity for a taste of a type of class D that I haven’t tried before – a Pascal Audio S-Pro2 module. I unfortunately missed buying a small lot of these a couple of months ago at a price which were at least the deal of the year if not the decade, but here was a single module at a reasonable price on a local classifieds side and so I could not resist buying that instead.

Pascal Audio is a(nother) Danish amplifier module company. It was actually founded by a group of ex-ICEpower people and although there are some clear similarities in product portfolio and product thinking, most of the Pascal products are focused on professional, PA- and musical instrument applications. This does show in things like power levels, channel configurations and module features. However, Pascal have also managed to creep into several hifi brands including Gato Audio, Jeff Rowland Design and many others – even edging out ICEpower from some of them. Irrespective of that, the quality reviews I’ve seen range from app. “massively better than ICEpower and Hypex” to “horrible sound and very poorly engineered”. As usual, the truth is probably somewhere in the middle but I guess we’ll see about that.

The S-Pro2 is a two-channel amp with onboard PSU that will do around 500W/channel in stereo and 1000W in BTL. This means it’s providing roughly twice the power of an ICEpower250ASX2 in almost the same form factor, making it (supposedly) the smallest 1000W amp on the market. As you can see from the pictures this version is an OEM-version without the usual aluminium base plate, which actually doesn’t bother me since it should make mounting the module to a “proper” heatsink much easier (and yes, even at 90% total efficiency a 1000W amplifier & PSU combo is still going to need pretty serious heat sinking if you want to get close to full power!).

While I do (sort of) have a specific project idea in mind for this module it’s going to take a while. First step is to (attempt to) develop a proper adapter PCB for the 26-pin signal connector to break the various module connections out to something that is easier to work with. Once that is done I’ll move on from there to some real testing, but that will definitely take some time 🙂

An early Christmas present…

I generally make a point of buying myself a Christmas present every year and this year it came a little early 🙂 While I was looking for the Hypex Ncore module I wrote about a couple of weeks ago, a stereo ICEpower700AS2 popped up as well – so I bought that 🙂 This is going to be a “little brother” to my 700ASC-monoblocks but whereas the monoblocks (which I also hope to finish over this Xmas break) have added buffers and dual-input switching, this is just going to be made into a simple and no-frills power amp.

In contrast to the Ncore module the ICEpower amp has onboard heatsinks so mounting in a small(ish) enclosure should be fine – at least for home duties. As I already had a basic layout for both a bottom plate and a back panel, drawing them up was quite easy and the back panel order is already placed. The support PCB I did for the monos also works here which should mean that once I receive the back panel there should hopefully be very few blockers to wiring up the amp and getting it tested within the next weeks.

I have seen one comparison of the Ncore and the ICEpower module (although I can’t find the link at the moment) with the Ncore coming away as the clear winner, but I am looking forward to seeing if my own conclusions match that 🙂

(apologies for the poorly lit pictures, but winter in Scandinavia means no daylight when I get home from work :D)

Encore?

A quiet last few weeks here – at least on the surface. Two reasons for that really: 1) With an Xmas-break looming on the horizon the pace at work is picking up a bit and 2) for quite a lot of projects I am in the annoying phase where lots of important work is done, but it doesn’t really look like you are getting closer to a finished product and so it’s not really worth showing here. If nothing else though, it’s nice to have a good pipeline for next year 😉

However, one thing there is always time for is to buy new projects for the shelves 😀 As regular readers will know I have made lots of ICEpower-based projects, but practically nothing with the various Hypex-modules. However, recently one of the new Ncore NC502MP modules came up on ebay and so I pounced on that. The module looks very nice but I need to test it for a while to check the sound (waiting for proper cables at the moment) and then I’ll decide on a suitable enclosure for it. The original goal was to built a custom high-power integrated amp, but I may end up going in a different direction and do a pure power amp instead. One deciding factor will definitely be whether mounting the module on a simple aluminium bottom plate proves to be enough heat sinking, because if the module has to be on a “real” heat sink, then all my current enclosure ideas are definitely out the window!

Soundwise, I still expect that the benchmark for the Ncore to beat (at least in class D) is going to be my trusty 125ASX-based stereo amp and the 700ASC-monos (which incidentally are also among the designs that are I am currently inching closer to completion…)

In search of synergy…

Slightly off-topic post, but I have written a few times about how I think that system-matching is much more important than any “absolute” sound quality, at least as far as enjoying the music is concerned. Well, today was another reminder that I still think this is the case 🙂

A couple of months ago I got new speakers, trading my old (and much-loved) standmount Sonus Fabers for some floor standing Scansonics that offered a bit more low-end slam. I was quite happy with the trade from the beginning and I have absolutely no regrets, but after a time the inevitable restlessness sets in and you start thinking about change (at least I do…). I’ve been running the Scansonics with a simple 125ASX amp on my Harman/Kardon preamp, but just to try it I dug out another ICEpower-amp from my collection, this time based on the older 200ASC-modules.

Although I would definitely still class the 125ASX as the better amp overall, the Scansonics (which are just a little bit bright) immediately benefitted from the more “closed-in” presentation style of the 200ASC, so as usual after initially listening to half a track I started to go through my normal playlist of tracks I know well and just enjoyed listening to some music that I would normally say I know back-to-front already.

To be fair I am honestly not surprised at this, because I saw the same change when I switched from the even older Elac speakers that much preferred the warmer sound of a 50ASX amp whereas the Sonus Fabers really came to life with the more lively presentation of the 125ASX. However, I still think that it’s nice to be reminded once again what really matters when putting a well-rounded system together and of course experimentation is always fun (although it can sometimes be very expensive as well…)

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 😀