Project files: Single-supply experiments…

After a short delay caused by me finishing the HF-lineamp writeup first, here are the promised project files for the single-supply minipre and the railsplitter mentioned in the previous post about my USB-C experiments. Although these two designs are pretty different, I’ve decided to group them together because they also have some things in common that would otherwise be a bit repetitive.

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Project files: The HF Line Stage…

Like the NE headamp this is another ancient amplifier design by a (now-defunct) Danish magazine – “High Fidelity” – that I wanted to try out. I’ve therefore redone the original PCB layout and since it is a bit of legacy design for a fairly narrow audience, I am publishing the files directly in case anyone else wants to give it a go 🙂

Is it an exceptional design? – probably not. However, while I haven’t tested this in a big setup I have to say that I was pretty impressed with the clarity and level of detail on offer when I did a quick test on my desktop, so it’s very likely that I’ll try putting the prototype boards in a case at some point.

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USB-C experiments – part 2…

As I wrote about a few weeks ago the USB-C power supply standard might open up a few new possibilities for DIY designs. Having recieved some PCBs now, it turns out I was right… 🙂

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Full house?

After this short break the shopping channel continues… 🙂

As I’ve mentioned before I’ve owned and listened to nearly all the standard ICEpower modules ever made. The only ones I’m missing are the 300AS1 (the last – and according to some people the best – ICEpower module that’s made purely with discrete components), the TI TPA325x-based 100AS2/200AS2 and the ICEedge-based 1200AS2 and 300A2/400A2. Well, this week I took a step closer towards the goal of trying them all because I received both a 200AS2 and a 300A2 in the mail.

These two modules are of course each interesting in their own way, but the all-in-one design of the 200AS2 makes it a bit easier to work with. As a result, I’ve already got a pretty clear plan for what to do with the 200AS2, and while I – sorta, kinda – also have a plan for the 300A2 it is going to be a bit longer. For now I’ve only done a quick check to confirm that the modules are OK though.

The main reason for the delay in building with the 300A2 is that I didn’t buy the matching 1500S PSU because it was far too expensive. While I already have a main PSU that meets the required specs, the rest of the supply arrangements will need to be worked out. That possibly requires me to do a new board layout, so while I’m anxious to try out the amp and hear what ICEedge has to offer, it might well take some time before I get to that.

I actually also ordered a pair of 300AS1s in the same week as these, but it turned out the seller wasn’t able to deliver anyway and so I ended up with a refund instead. Oh well, the hunt for the last few ones continues then 🙂

Powering new projects?

I don’t really want to turn this blog into “the shopping channel”, so before I show you more stuff that I’ve bought just for the h**k of it, let’s look at something that has more of a practical application 🙂

The background is that I bought a small ZK-4KX buck/boost PSU module on Aliexpress a while ago. It arrived a couple of weeks ago, it seems pretty good and the “boost” functionality makes it extremely versatile as an extra power supply (“boost” means that it is able to provide an output voltage that is higher than the input voltage). I looked up reviews etc. and found a youtube-video where someone built a bench power supply using one of these modules and a small USB-C power board and that I found very interesting.

In my mind USB-power is still 5V and 1-2A output at most. However, with USB-C that clearly isn’t true anymore and with up to 20V and several amps on tap, suddenly powering other circuits – even small power amps – is within reach. The reason this is interesting is hopefully quite clear. In my experience power supplies are still sometimes a bit of a pain for DIY’ers. Not only because it can be difficult to find good solutions, but also because mains wiring scares off less experienced DIY’ers (although I am sure some would argue it doesn’t scare off as many as it should 😀 )

I also have a gripe about “bespoke” external power supplies from a more basic engineering POV, namely that replacements are hard to find and so – as anyone who has spent hours looking for a specific offboard PSU for a device will attest – interchangability would be a big bonus.

Sensing an opportunity here, I bought some of the small USB “decoy” boards and also (because that was what I first thought of powering with it) a small TPA3221-based amplifier board. The TPA3221 is the replacement for TI’s previous TPA3116 chip and while it’s not the last word in sound quality and it will not give full power with a 20V supply voltage, it’s still worth putting 20 dollars or so into I think.

Having just received the boards yesterday I have no detailed impressions. The USB adapter seem to work well and they give close to 20V output (with the PSU from my HP work PC, which is what I have at the moment). They’re obviously not really suited for case mounting, but on the other hand the small ones are so ridiculously compact that I think that is definitely a solvable problem. The power amp board is around 55 x 100mm (so a bit longer than a credit card) and the small USB-C board is only app. 10 x 18mm including the protruding connector.

I also started looking at my own “back catalogue” of boards and found a couple of designs that – with small modifications – could be USB-powered. Those boards should be here within a couple of weeks so I can do some experiments with those as well (and no, I’m not telling you which designs they are yet 😉 )

Competition arrives…

A few months ago I showed off the Hypex Fusion plateamps that I intended to use for my active speaker project. While I did get the Hypex amps up and running on Windows I haven’t really used them for anything yet though.

My first excuse for that is that the weather has been a little uncooperative in terms of outside woodworking for a while now, but I am hoping it changes soon because I haven’t been able to make that much progress on my speaker projects yet.

The second reason is that while I did get the Hypex amps running I have been secretly hoping to find a pair of MiniDSPs instead. Not because of the sound (haven’t really tested that) but purely because of convenience/practicality. Firstly I will be able to control the MiniDSPs directly from my Mac and secondly the MiniDSPs can be connected to a network via ethernet and not just via USB to a computer as Hypex uses.

This week my patience (or is that procrastination?) paid off as I was able to grab a pair of MiniDSP PWR-ICE250s off my local classifieds page. These are new (or nearly new) and bought from a seller who – like my first venture with the PWR-ICE125s a few years ago – bought them for all the opportunities they present but never managed to get them off the shelf. I didn’t really need the extra power of the 250W version but I think these will do fine and the price was not bad.

Another advantage will be that these are acually mechanically better suited to my floor-standing design. And of course, it means I have the Hypex amps left over for (potentially) activating a small monitor project as well.

In short, I really hope the weather improves soon… 🙂

It’s an anniversary!

…well, actually it was yesterday but who’s really keeping track?. And besides, the year has been a bit odd anyway so it seems fitting that I break with conventions here as well.

It’s been eight years since I started writing, and although the pace has slowed a bit I am definitely still here. I am also very happy that many of the regular readers continue to hang around and engage with questions and comments – extremely grateful for that.

There are a few recent developments that I look forward to showing as soon as I can (mostly they’ve been held up by postal delays and a lot of pressure at work) and in general the DIY pipeline is as full of projects as it has been for the past eight years.

As always, thanks for reading and I’ll look forward to the next year (ok, 364 days…) 🙂

Project files: IRM PSUs from a different angle…

Here is yet another version of a couple of PSUs based on the Mean Well IRM modules. I’ve done these before and the post title basically comes from having simply turned the module 90 degrees to make a more compact footprint – I know, not exactly a revolution… 😊

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Easter breaks in Denmark are quite long and as the weather cooperated part of the time, I did manage to squeeze in some audio-related activities 🙂

A while ago when I launched the version 1.5 of my “mini-pre” a reader asked if I had done any comparisons of the different opamps I suggested and I replied I hadn’t. On one hand I’m surprised that I can even hear differences between opamps, but on the other hand when you think about it it’s a bit like replacing a whole amplifier and then it is of course a bit less surprising that changes are audible.

Now, I am always a bit hesitant to make recommendations for opamps based on just my own sound preferences and my limited testing, but on the other hand I have done opamp comparisons in the past and my impressions haven’t been far off what I have been reading elsewhere. I also found the comparisons to be very useful for myself and since it has also been a while since I’ve really tried the newer opamps on the market I started thinking it would be worthwhile to try comparing a few types again.

Actually doing comparisons in practice is a different matter though as the newer ICs are only available in SMD packages and so I had to pick a more “brute force” approach than the usual method of just swapping DIP opamps. I could have used DIP adapters, but I wanted to be sure that there were no oscillation issues etc. and so I decided to build an extra preamp instead with a different IC. These two boards are therefore completely identical except for the choice of IC – even the two Alps pots come from the same supplier so nothing is left to chance (well, sort of, anyway – plenty of variables left still 🙂 ).

The original amp has the OPA1656 and the other has the OPA1642. From what I know the OPA1656 is currently the highest-spec audio grade standard opamp that TI offers. The OPA1642 is “one step down” but still very highly rated, and it is JFET-input which should give a low enough DC-offset to be used directly in this kind of application. The bipolar input “equivalent” to the OPA1642 is called the OPA1612 as far as I know.

Not quite ready to post my listening impressions of these two ICs yet, but it’s been quite a good exercise to try comparing opamps again – and yes, I can still hear some differences 🙂

Two of a kind…

If I showed off every blank PCB I’d bought over the years I’m not sure this blog would feature much else. Also, it would give away just how many projects I really plan/start up but never finish and I don’t really want to do that either 😀

However, here I’ll make an exception because these two boards were both bought from Aliexpress on the same day, they arrived on the same day (from two different vendors) and they are actually the same basic design – a John Curl-designed JC-2 discrete preamp.

Obviously the boards look far from identical, but the amplifier sections are the same. What’s different is the power supply and a few selected parts and implementation choices. On the large board, the power supply is a dual-mono discrete regulator. On the small one it is a pair of 78xx/79xx regulators shared by the two channels. On the small board there is an onboard volume pot but no output caps, on the larger board it is the other way around etc. OK, to be fair the large board has a pair of higher-biased output transistors added, but again, the input stage topology and parts choices are essentially the same so these two have a lot in common.

Apart from being interesting comparisons, both to each other and to the balanced JC80, I am always intrigued by these simple discrete circuits – what can they really bring in terms of sound quality?. The JC-2 has received quite a lot of discussion (scrutiny…) on diyaudio with even John Curl himself chipping in, and I’m sure there are ways to evolve and improve the circuit. However, that’s not really what I aim to do with a pair of ready-made boards.

Plans for the boards? Well, yes and no… The large board is probably going to be a stand-alone preamp eventually. With the discrete regulator and the space for good-quality caps etc. I think it must showcase more or less how much it is possible to squeeze out of the relatively simple JC-2 design. The small board was attractive for a different reason though – the onboard PSU arrangement means that it can be powered directly from an ICEpower module (or a similar class-D amp), so if it sounds any good, here’s an easy and compact way to build an integrated amplifier – hopefully it sounds good too 🙂