Project files: HackerCAP PSU clone…

In response to a request from a reader for these files. Not sure why they never never published, but they work well and seem fine so here you are 🙂

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Last of a dying breed?

Yes, this is a DAC and no, those are not a dying breed as such. However, it is an AKM-based DAC, and since the main AKM factory burned down last year, those have been dying out as the supply of ICs dried up. I believe AKM is planning to restart production of at least some of their ICs but I am not sure when, and the reality is that DAC design is pretty complicated and so they may not be able to win back the customers that they have lost when they do eventually restart production.

I was reminded of this by a recent blogpost from Jason Stoddard of Schiit Audio that deals with exactly this problem as Schiit was one of the AKM customers and they have had to convert their products to ESS DACs instead. As I think I have mentioned in the past I have tried several ESS-based DACs and somehow always found them impressive at first, but tiring in the long run. Not sure why but that’s just how it is and so I am obviously not enthused by an outlook of nothing but ESS-based DACs in the future. The DAC chip at the heart of my board is the AK4497, so not quite top-of-the-range but still a part that is/was used in several very expensive commercial products.

The background for this build (which I completed a few weeks ago) is simply that I came across this unwanted kit on diyaudio.com a few months ago. The price was pretty good and since it was (almost) complete but still an unassembled kit, I had the opportunity to add my own touches to it – which is exactly how I prefer it. It’s also got a few details I like, such as the onboard connectors and the muting relay on the output, so for the price I paid I thought it was a bargain.

No concrete plans for the board just yet, but having a DAC with all inputs available is very nice as a kind of “future-proofing” for a digital signal chain. The board even takes a separate USB-module which I don’t need right now, but still plan to add for the sake of completeness.

Blink and you’ll miss it?

OK, so it seems I just blinked and three weeks went by….that’s how it is sometimes I guess.

Anyway, what has happened in that time? Well, my “staycation” holiday came and went. Decent weather so I managed to get a lot of stuff done at home, but – as usual – not as much as I wanted to. The “downtime” from work was much needed, but to be honest so is getting back to work and finally getting out of the house a little again.

Audio-wise I did manage a few things during the break, but in what I guess can be called my standard pattern it was very much: “finish two projects – start three new ones”. I don’t know why I never learn to be honest…

Apart from some layout work where I am waiting for PCBs to be delivered, one of the “newcomers” to the project list is actually very much an exception to an established pattern – because it is a Pass amplifier that works in Class AB! Called the AB100, it’s a design that Nelson made for a customer who didn’t use it or pay for it. Instead it was “open-sourced” to the diyaudio community.

The initial posting is very old now and I’ve seen the AB100-design before, but this time around I realized that diyaudio-member Prasi had open-sourced some gerber-files of his PCB-layout. Prasi’s layouts are usually very well done, and as I had some room in a PCB order I got some boards delivered. I’ve also ordered the parts I know I don’t have (transistors etc.) and so I hope I either have the rest in stock or can manage to work around the “out-of-stock” messages for even the most trivial parts that seem to be inescapable these days.

I also made some progress on some speaker work – thanks mostly to the “work-outside-friendly” weather. However, when that progress will be turned into something I can actually show off here is an entirely different discussion. For now I’ll settle for seeing if I can pick up the posting pace a little over the next months 🙂

Dead on Arrival?

Isn’t that what “DOA” normally means? Fortunately in this case nothing has died (yet!) and “DOA” instead stands for “Discrete OpAmp” 🙂

The background is that I have noticed that quite a few clones of various Bryston amps have started cropping up over the last year or two – not least the excellent BP26 clone I have built myself. On one of my PCB-searches I was looking into these clones and found a small dedicated headphone amp that looked interesting. However, looking at the PCB layout I honestly wasn’t particularly impressed and a small “I can do this better” thought started forming at the back of my mind…

Some more digging revealed that Bryston is one of the (few) companies that publish schematics of their older models which would explain the surge of clones – these schematics are obviously a great resource. I started looking through the schematics and found that a lot of these products are build around the same “DOA33” discrete opamp building block. That’s obviously interesting since Bryston’s commercial products tend to be well-regarded and that gave me the idea to do a version myself, but with the modular “opamp” concept intact. As a replacement for an integrated opamp this is probably a stupid idea, but as a way of building compact and modular discrete amplifiers it’s not so bad I guess.

I started doing some layout work and eventually ended up with an all through hole design of around 45 mm squared that I was quite happy with. As a “mini-evolution” of that design there I also did an SMD version (with SMD passives) which I still need to test. The idea being that it can be smaller (I could have done more here), that SMD passives can actually be had better/more accuarate (and for less money) and that it would be possible to get the SMD pasives mounted professionally and relatively cheaply by one of the PCB companies that also offer assembly service. Then it would be possible to have a drawer full of “building blocks” and then simply mount the leaded parts (mainly matched transistors) when needed. I didn’t get to that just yet, but I might explore the idea again later.

To accompany the DOAs, a series of “baseboards” would be required to provide space for the external components required. The baseboard shown here (and the only one I have done so far) is the most simple circuit to build a basic preamp, i.e. similar to a CMoy-style amp with an integrated opamp, and is probably most accurately described as a “test bed”. to confirm that the opamp circuit works. The baseboard just includes the various gain setting resistors, some PSU caps and an output capacitor to get rid of any DC on the output.

What I am looking into next is one of the more “advanced” circuit variations that Bryston describe, namely a headamp (with a DC-servo to get rid of the impractically large output cap for headphone impedances), a RIAA (with two modules per channel) and also a specific preamp with the volume pot isolated between two gain/buffer blocks (similar to Bryston’s own designs) etc.

I may end up more or less “full circle” back to the BP-26 design I originally came from, but then at least I will have had some fun along the way 😀

Babysteps…

The “official” summer vacation period in Denmark is coming to an end, which means that thanks to careful planning my vacation period is just getting started 😀

That means two full weeks off from work with (for once) no plans to really go anywhere except some day trips. Instead, I have a very long list of audio- and non-audio diy-projects to work on – if the weather permits and nothing better comes up that is 😉

Top of the list is that I have been eying a lot of the half-finished projects taking up space, so with any luck I’ll get started on some cabling to get some of those boxes finished up and out of the way. I normally don’t like cabling very much, but once i get over the initial “I don’t like this”-stage it tends to be easy work, and I expect I have all the supplies I need on hand (fingers crossed).

Also near the top of the to-do list is a handful of partially assembled PCB projects, mostly started because a couple of months ago I couldn’t really summon up the energy to do anything execpt a little layout work and a lot of online-shopping. These projects are also progressing, but – as the post headline alludes to – quite a bit slower than I had hoped for. The reasons are manyfold: back-ordered or unavailable parts (due to general supply-chain issues I imagine), incorrect deliveries (Digi-key’s fault), procrastinated parts orders (my fault…), cocked-up PCB orders (my fault…), PCB design errors (also my fault…) and so on.

The picture shows one of the boards that actually worked the first time – a PSU for a small class A amp based on larger IRM60 PSU modules. Sadly, the matching amplifier PCBs didn’t work the first time, but hopefully I can showcase the full set once I have figured that one out.

The upshot of all this is that a few of these projects actually turned out to be welcome opportunities to make use of parts I already had on hand (more on that later), while the others just sort of stopped when I ran into parts I didn’t have…

Anyway, much of what is missing should trickle in over the next two weeks and so let’s see what sort of progress comes out on the other side. If you have had a summer vacation already I hope you’ve enjoyed it. If – like me – you are just getting started on your time off, I hope you make the most of it 🙂

If it’s not broken…

… modify it until it is!

Not sure I’ve ever posted an example of me destroying something that otherwise worked perfectly well. That’s not because it didn’t happen before (on a number of occasions…) but because I think this one is worth showing off 😀

The background is that I bought a small TPA3255-based amplifier PCB along with one of my recent Aliexpress purchases. This is called the Shui Yuan amp (diyaudio-thread here) and it costs somewhere around USD 30 incl. shipping. The TPA3255 has got a reputation as a good amplifier and since I have a few suitable PSUs I put one in the shopping basket.

I received the board, checked it and confirmed that it worked well. Very importantly there were no nasty turn-on/turn-off thumps and the sound quality was definitely promising. Having thus confirmed that it worked and sounded very well, I set about making it sound even better… The obvious (and intended) modding object is of course the input opamps (NE5532s – as usual of questionable origin). These are socketed and so very easy to replace.

However, there are also some interstage coupling capacitors which are Nichicon FW polar electrolytics. They look genuine, but since I have a bag of Elna Silmics that are supposed to sound better I wanted to change those as well. Also the two main power caps were a bit tall for my liking, so I wanted to replace those with some shorter ones to ensure a good fit in a 1U case.

In principle this is all a simple job, but in the middle of the desoldering process I realized that I was not only removing solder but also quite a few of the pads on the underside of the board. Pretty annoying, and very difficult to do anything about on a double-sided black PCB where you can’t really see what you are doing. The culprit here – apart from my lack of desoldering skills – is obviously that I forgot that this is a cheap product on cheap PCB material. It’s not impossible to fix, but it’s not easy and right now I’d probably not spend too much time on it – oh well.

From what little I heard this is a great amplifier PCB at a reasonable price though so if you want to experiment I would definitely recommend buying one (but consider limiting your mods to replacing the opamps … 🙂 )

Closer to the edge…

As you probably saw I added an ICEedge-based ICEpower300A2-module to my collection not so long ago. I originally envisaged this as a long-tem project because the module requires a fairly complex PSU (with five supply rails) and I didn’t want to “splurge” on the matching ICEpower PSU (too large and too expensive).

However, for a different project I was looking through Aliexpress for cheap switching Power Supplies and I then spotted the option of customising some of these PSUs with the specific voltages you want. That was definitely an interesting turn of events, not only because the Aliexpress PSUs are massively cheaper than the ICEpower PSU, but also because it is much smaller and allows for a 1U case to be used. That gave me a case design idea as well, and so I bought a PSU without having ever held one.

Having received it now it seems to be well-made and the output voltages are more or less spot-on what I requested – great!. The 250-300W power rating is probably a little on the low side, but for a bit of evaluation and home use I think it will do just fine. I haven’t tested how noisy it is, but again for a quick test it’s probably more than plenty.

Now am sure you hear about parts shortages all the time these days and this project is also somewhat affected. It turns out “the missing pieces” of the puzzle in this case are rather small, namely the double-row JST connectors for the ICEpower modules control and low-voltage power connections – very annoying. I couldn’t find them in stock fro any of the “normal” sources that I am actually able to order from. I think I found a place to order these now, but probably with at least two-week lead time and possibly more. Let’s hope they actually show up 🙂

Lots of other things going on the mean time though, including a new PCB project I am quite excited about so even if we are heading into the holiday period then expect more updates coming later 🙂

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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