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 🙂

More MeanWell IRM PSUs…

As regular readers will know I have been using the Mean Well IRM-series AC/DC PSU modules quite a lot. There are many positives to these modules (size, cost, standby consumption etc.) and only a few downsides, mostly the limited output voltage options and the rather noisy output. The noise doesn’t matter so much when used for auxiliary supplies, but for things like preamps, headphone amps etc. I’m sure it’s possible to do better.

However, because the IRMs are a switching design with a relatively high switching frequency (app. 100kHz), cleaning up the output on the IRMs should be relatively easy with just a passive “Pi”-filter (CRC or CLC). Because of the high ripple/noise frequency even a low series resistance/inductance and a little bit of extra capacitance should have a dramatic effect. Some time ago I started making a single-rail PSU based on an IRM-module for a clean and compact 5V supply for my “Music Box” project, but I realised that actually these would be applicable in many projects so I ended up with several different versions (single/dual, different power levels, integrated/separate filtering etc.)

As I’ve just received what I think is the last variant, an integrated dual version with space for two 15/20W IRMs, now seems to be a good time to collect everything and release the project files so they will be up as soon as I am back from my summer holiday in a week or so. Until then, I hope you enjoy the summer 🙂

Back to the future – of DACs?

For pretty much as long as I can remember, there has been a DAC “arms race” going on where manufacturers competed to give the biggest numbers – 16, 18, 20, 24, 32 bit resolution and 48, 96, 192, 384, 768 kHz sampling rates. Irrespective of whether you had the source material to make use of these massive numbers – or even whether the laws of physics made them obviously pointless in the real world, the “bigger number is better” philosophy was still adhered to.

For a few years though, some people have been going “back to basics” with DAC chips such as the TDA154x and others, as wells as discrete “R2R” dac designs such as the Soekris boards and the Schiit Multibit converters. These designs often don’t offer the full resolution of high-res material, but if you don’t care about that – or if you are still listening primarily to 16/44.1 material – then they offer something else, namely a different (many would say “better”) sound. I’ve previously written that I find the ESS ES90xx dacs to often be very impressive at first, but after a while I get a bit of listening fatigue. It could be me or my imagination, but it’s happened enough times that I start to see a pattern (at least when system matching doesn’t mask it) and so I have been trying to stay clear of ESS-dacs and see what else is on the market.

Now, as usual for this I don’t really need another DAC, but I am still curious 🙂 Not quite curious enough to splash out on a Soekris board to play with to be honest, but still curious enough to clicking the “buy it now” button on ebay for this board. It’s based on the AD1865 IC in dual-mono configuration and once again what pushed me over the edge was that I could get a half-finished board with SMD components soldered, so I had some influence over the design of the board.

Assembly was quite easy because I only had to pick and mount the through-hole parts, but even that was enough to make me remember how much I hate black PCBs. Not only because the seller showed that the board was green in the picture, but also because this is a matte black finish that I haven’t seen before and which makes it 99% impossible to see any traces on the board. Fortunately everything worked the first time, but if it hadn’t I am not sure I would have bothered with that much troubleshooting before giving up. Manufacturers: I know green PCBs are considered “boring”, but they WORK! or if you desperately want something else then blue or red still allows you to see the traces, so please stick to those colours. (OK, rant over 🙂 )

The board has one coax input. I opted for a BNC here because that was the socket I had on hand and that might end up being a mistake, but it works now (with an adapter). There’s also an I2S input meaning it’s possible to connect a second source such as a USB card or similar. As usual, I’ve only done basic listening testing with “baseline” I/V opamps (the OPA2134 and the LME49710) but it’s definitely not making a bad first impression 😀

Not quite sure what to do with this one yet, but possibly a “Music box” version 2? Anyway, more listening impressions to be added later I guess.

Idling…

Another long break since the last post, but to be honest nothing much has happened over the last few weeks. I have been waiting for some PCBs to turn up and have been busy with non-audio related DIY as well. I’ve also added a few new empty boards from eBay to the project pile but that’s about it.

The PCBs I have been waiting for from manufacturing were a simple dual-PSU based on IRM-modules and another Borbely design – hopefully I’ll have those populated in a few weeks so I can showcase them.

I’ve also previously promised myself to resist the urge to take up more loudspeaker projects, but a few weeks ago a MiniDSP PWR-ICE125 amplifier popped op on my local classifieds page at a reasonable price so now that promise has been broken as well.. No concrete plans yet, but one of the things I’ve investigated before is how to do a “soundbar/soundbase”-style active TV-speaker and some DSP-capabilities would come in handy there. I’ll start by looking at the drivers I have in stock and see if there is anything that be used for that purpose 🙂

Oh, and a final moan about parts availability. I was browsing through Mouser the other day trying to find an 7905 regulator in an isolated package. It looks like JRC are discontinuing some of these negative variants, which is a bit alarming. I genuinely never thought I’d see the day where I’d be concerned about availability of things like three-terminal regulators and BC54x-transistors, but here we are. On the plus side, I’ve noticed that some of the newer audio-grade opamps from TI (OPA16xx) are surprisingly cheap (but of course SMD only) so it’s not all bad but in general parts availability for “normal” diy’ers is declining so rapidly that you can either worry, stockpile or both! 🙂

Bryston BP26 preamp clone…

Even though my pile of finished (and half-finished, and not-even-started-yet…) projects seem to be steadily growing, I can’t help but keep an eye on eBay for new and interesting designs to add to it. I’m not sure I can describe fully what makes a design “interesting” to me, but something about how it looks, how well thought-out it seems to be in terms of features, whether it seems to be well-engineered and also whether it’s fully-assembled or PCB/kit so I can influence component choices etc. myself – and of course whether it looks like good value.

The latest thing I stumbled upon was a blank PCB of a (supposed) clone of a Bryston BP26 preamp. To be honest Bryston is one of those brands that I know about but have never really had any particular opinion about. I get the impression that their stuff is solid and well-engineered, but their representation in Europe is sketchy and the design of their products has never really managed to catch my eye. However, regardless of the supposed provenance of this kit – you never really know how close to the original these “clones” actually are – a fully discrete preamp design with both balanced and SE inputs is definitely interesting. The board looked good on the pictures and as I had most of the expensive components (connectors, relays etc. ) and quite a bit of the other stuff on hand already, I decided to take a chance on it.

Normally the quality of these ebay-offerings is a bit hit-and-miss to say the least, but this one I’d place firmly in the “hit” category. The board is good quality and it is supplied with documentation that is well above average for what you can expect. Full, readable pdf-schematic, full BoM (with just a few untranslated comments in Chinese that you have to work out), a basic adjustment procedure (only one trimpot per channel) and – something completely unheard of – a mechanical drawing of the rear panel cutouts for the connectors!.

The board came together quite easily, and although it took a while for me to operate the input selector correctly during testing to actually get sound (…) there were no real issues getting it to work. The board seems stable and well-behaved in initial testing, meaning no nasty turn-on/turn-off thumps, no noise and no unexpected spikes in DC-offset or bias at any point.

Normally I’d try and finish the full pre as quickly as possible, but this time I’ve chosen a slightly different strategy. I’m going to listen to the board in my own system before i decide if I want to commit the extra money for the final enclosure (mostly because a customised back panel is probably going to cost about the same as all the other components combined). While I am waiting for a PSU board that should be here in a couple of weeks, I’ve repurposed an old bottom plate into a makeshift test bottom. Let’s see and hear what this thing can really do then 🙂

Music Box…

For some time now I have been using Raspberry Pi-based music streamers in combination with Volumio as my primary signal sources. On the hardware front I have both analog and digital versions of the Hifiberry Pro+, an Allo Mini Boss and an ES9018-based DAC HAT. However, to see if I could push the quality up even further I wanted to try and do something myself as well.

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Wooden amps…

Well, not completely wooden of course! Some years ago I showed a plan to make a set of amps with wooden front panels, because I picked up some pre-cut wood in the right dimension on one of my trips to Japan. A while back the plan was resurrected, but then immediately brought to a halt because I had to enlarge some already-drilled holes and managed to destroy one of the panels in the process – bummer!

However, in the mean time I’ve found a local place that sells wood trim pieces for professional craftsmen and in their assortment I found a pre-made profile in the right dimension for a 1U panel and in several different kinds of wood. I chose oak as it is more my thing than the darker wood types and it goes well with both black and silver fittings. I’ve recently invested in a better drill press, so redoing the panels were without accidents this time and I also managed to overcome my fear (or is it loathing) of doing cabling to finally complete the set 🙂

The set consists of a DCB-1 preamp (on a clone board), meaning a DC-coupled version of the classic B1 buffer circuit, and a Hifimediy T4 Tripath-style class D power amp. The power supply is a surplus N2 XL375-type which I bought a small stash of some years ago.

No detailed listening impressions from my main system yet, but on test speakers it sounds excellent as I expected from what is basically an “evolution” of my old B1/125ASX bedroom system. Both components include relays to minimise turn-on and turn-off thumps and so as a set they are well-behaved enough for daily use (which is always one of my success criteria). As far as the looks are concerned, I could honestly see this being something I will want to try again in the future…

Buying “suspicious” parts…

With the current trend in audiophile parts being that all the “old” audio grade parts that we know and love are either being discontinued outright or at least replaced with something in impossibly small surface mount packages, it’s almost inevitable that we all at some point face a choice between giving up on a project and sourcing parts from “questionable” channels such as eBay or Aliexpress.

Here are the questions I personally ask myself before buying something and while they are definitely not a guarantee against wasting your money, they might help someone decide when to take a (calculated) risk and when to pass up what otherwise looks like a good opportunity.

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The last F5?

I’ve built a couple variations of the F5 already and I have a couple more that haven’t been finished yet, but the last one of them is here. It’s a pair of mono blocks with fan cooling and a large power supply 🙂

This project was of course driven by the fact that I really liked my original F5 build, but also by the fact that I had some suitable heatsinks and that I got a good offer on a couple of transformers that were really meant for a Pass/FirstWatt mono block build (2x18V/250VA each). The heatsinks actually turned out to be a mixed blessing, because they are just a millimeter or two too tall for most of the readily available enclosures, so I had to go up to a 3U size. I also decided to choose a slightly larger footprint instead of trying to shoehorn everything into a “real” half-width box. That annoyed me in the beginning, but to be honest I am not regretting that now.

Design-wise, you should be able to see the inspiration of some of my other projects in this one and that is no coincidence – there were some concepts I wanted to “recycle”. That last piece to arrive of what you see now was the rear panels which showed up a few days ago. Fitting them was a quick job, but they are quite expensive and so I can’t help but breathe a sigh of relief when they fit as I intended the first time. No matter how many checks and paper mock-ups I have done in the creation process it’s always a huge relief when everything works…

Still a bit of a way to go, but getting this far was very satisfying 🙂

The BoSoZ…

When I started to look around for balanced preamp designs some time ago, the BBA3FE wasn’t the only design that turned up. Another candidate was a sort of “predecessor” for it, namely the Pass Balanced Zen Line Stage (aka BoSoZ). I was a little slower getting started on this one so the BBA3FE came first, but a few weeks later inspiration struck and I managed to finish the layouts for both the BoSoZ and the matching PSU as well.

I chose a mono configuration for the amp board to maximize flexibility and minimize board cost. I’ve only made some minor changes to the schematic, but you should be able to see the resemblance to the BBA3FE layout easily. My prototype version uses 27.5mm output caps because I had some I wanted to use, but the “real” version of the board has space for 37.5mm caps as well and is only slightly larger (app. 5mm deeper).

As you can see I’ve actually also made good headway on the mechanicals of the design so what you can see now is really a semi-completed amplifier. Other than the new amp/psu boards I’ve picked components “off-the-shelf”, i.e. input selectors, an output relay board and an aux PSU that I have previously done, so putting it all together wasn’t that hard to do.

I need to pull myself together a little and get the wiring done before it will play music for real, but other than that it’s looking very promising – and the initial sound quality tests definitely match that as well 🙂