A pile of amps…

Not quite a New Year’s resolution, but still something that I have promised myself to do something about this year is my pile of unfinished amplifier projects.

Near the top of the pile – mostly because it didn’t need that much work – was my Pascal power amp (based on the S-Pro2 module). Late last year I got the front panel from Schaeffer which was really the only missing piece and all that was then left was to cable everything up. So to (hopefully) set the tone for the year I got stuck in and finished that this week.

No real complications with finishing the amp, apart from taking 3 attempts to dim the brightness of the ridiculously bright white LED in the switch to an acceptable level. I like the clean look of the white LEDs, but making a standard red or green LED into something that doesn’t burn your retinas out is just so much easier…

Other “lessons learned” include that I was happy I took the time to design a break-out board for the module, because the last bit of wiring was so much easier this way instead of having to air-wire everything to the same 26 pin connector on the Pascal module. Also, I should have moved the module forward another 10mm or so as the space for the mains wiring is a bit (too) tight for my liking, but it should be OK as it is now.

I knew the amp was working from previous testing, but I hadn’t really listened to it. Well, I have now (briefly), and while I still use the ICEpower700AS2 as my main amplifier and I think it has better synergy with my current speakers, there is no doubt that the Pascal module is a very capable amplifier. I no longer have the Hypex Ncore-amp I built to compare it with, but where I rate the amplifiers one of the things I notice is that – like the Hypex – I find the bass a little too pronounced with the Pascal amp. This is definitely a personal preference/synergy thing and the speakers and room will emphasize the bass though.

I’ll probably keep listening for a little while though, but as I was on a roll with building I managed to do a “facelift” of the 700AS2 as well (new front panel and proper switches for mute and standby). The wiring issn’t as pretty as I’d hoped for because I had to wire the LEDs to the respective PSUs instead of to the LED drivers, but once again the breakout board really helps. No changes in terms of sound obviously, but at least now the looks mean I’ll be happy to keep it on the shelf as well.

So, one (and a half) project done and the motivation to continue chipping away at the pile of amps has increased that much more – let’s see how the year moves on from here 🙂

New Year’s resolutions…

Well I don’t really do New Year’s resolutions as such (and not just because I can never stick to them anyway…), but starting a new year is still a good time to reflect on what to prioritise, change and improve for the coming year.

One of my goals for this year is definitely to get some traction under a couple of my speaker building projects. I’ve already started the woodworking and things are progressing so there is still hope on that front. However, once I get the mechanics worked out will come the hard (and interesting part) of experimenting with crossovers and tuning the sound.

As I have already decided to start out with active crossovers, I spent parts of the Christmas break making some temporary homes for my prototyping amplifiers. These boxes are just made from scraps of plywood I had on hand and they are definitely not pretty. They should however be functional, even in a semi-permanent setting as the projects (inevitably) drag on 😀

The amplifiers are 3-way Hypex Fusion FA123s and some readers might think “Hang on, we’ve never seen those presented before?” – and that is absolutely correct 🙂 I have two-way amplifiers from both Hypex and MiniDSP available for the projects I have in mind, but at some point I want to get to a real three-way speaker project as well.

Since much of the prototyping is is going to be “two-way and sub” configurations which is nice to be able to do in one setup if required, I looked at these. They come up occasionally as used pairs, but Hypex have been raising their prices regularly and so a Black Friday offer actually looked tempting enough to make me take the plunge and buy a new pair.

Next step: Getting some drivers into some cabinets and diving into the Hypex filter designer software – wish me luck!

Happy New Year!

So, 2021 has come to an end – and it’s been another unusual year I think.

At least for me in Denmark, most of the spring/summer/autumn-period was more or less normal, but both the beginning and the end of the year have been impacted by COVID-restrictions. Most presently for me is that I am writing this from home having had to cancel my original travel plans, but of course that is by no means the only (or the most severe…) impact.

As I’ve written previously I am probably in all honesty about the last person who should be complaining about the situation, but I’m well aware that not everyone has been this fortunate. I hope we’ll see a further improvement in 2022, so that we can move on without (necessarily) blindly going back to where we came from.

If you’re a regular reader here you may have seen my pace of posting slowing down a bit, at least over the last few months. There are a number of reasons for this and none of them are serious or permanent, but expect that the slow pace will continue for a while at least. I have had to remind myself on a couple of occasions that this is only a hobby, but I will of course continue to post stuff whenever there is time and inspiration available 🙂

The upside of (another) turbulent year for me is probably that whatever 2022 will bring, I think I’ll be ready for it. Happy New Year to everyone out there and stay safe in 2022!

Small wonders?

Every year for at least the last 20 years I have made a point of buying myself an X-mas present (OK, the last few years it’s been more like a handful of presents, but nevermind that…).

Picking something out has usually been done with the help of three guiding criteria, namely “shiny” (= something that is a little out of the ordinary or feels special), “expensive” (= not necessarily in absolute terms, but a step above what I would typically spend), and “unnecessary” (= something I didn’t need, but still wanted 😊 ). Admittedly these goals were more relevant back when I was a student and the budget was tighter, but consciously buying stuff that is a little out of the ordinary in this way still feels worthwhile.

This year I have bought quite a lot of speaker drivers and so it was sort of appropriate that I ended the year with buying one more pair. It’s a pair of small Seas L12RE/XFC coaxials that I came across at a good price. I’ve wanted to try these more or less since they were launched but the price was a bit too steep, however at very nearly 50% off list price for this pair I had to take the plunge.

I don’t really know why but I have had a keen interest in coaxial drivers for a long time. It probably started when I originally began working in a hifi-store that sold KEF speakers equipped with KEF Uni-Q coaxials, but it might also have something to with the engineering fascination. Coaxial speakers are at the same time both a brilliant and a deeply compromised idea, but they often achieve a perceived sound reproduction that many other speakers struggle to replicate.

Apart from these coax-drivers, I am also regularly eyeing the various PA-coaxials available to make something with a pair of those as well. The problem there is that PA-coaxials are normally very bass-shy (because they are meant to be used with subwoofers), or very expensive (or both!). Who knows, maybe that’s next year’s present? 😉

The first stop for this pair of drivers is probably a small vented box like in the Seas application note but depending on how that turns out I might also (eventually) experiment with a 3-way stand mounted design where these are the top and middle section together with a woofer.

Unexpected incentives…

As i wrote in the last post I haven’t exactly had a ton of time to work on DIY lately. However, sometimes a bit of inspiration comes in that makes it little easier to focus and get something done…

In this case, it was an email from Schaeffer a few weeks ago informing me that they were going to increase the prices of both raw materials and labour to cover COVID/supply chain/whatever-related input cost increases from the 1st of December. No issues with that as such, because I can imagine running just about any manufacturing business these days isn’t easy, but of course the prospect of price increases was a good incentive to place an order – or two – before the deadline.

Now the Schaeffer/FrontPanelExpress front panels are very nice and the service is a fantastic help, but to be honest it is also a bit expensive for a hobbyist, especially if you (like me…) are better at starting up new projects than finishing the old ones…

I have been contemplating various alternatives to the Schaeffer panels for a while, but so far I haven’t really been able to come up with anything. So, faced with an even higher bill than usual I took a look at the project “backlog” and ordered a few rear panels (which you can see here) and also some front panels (still in transit) for a couple of projects I should have finished ages ago.

Given the current pace of my builds these should keep me going for a while – stay tuned to (eventually) see what they will be used for 🙂

Project files: A different F5…

Would love to say that I am extremely busy with loads of interesting DIY projects and that’s the reason why I haven’t been posting much lately. Unfortunately it’s mostly just the usual “pre-christmas” panic at work that is keeping me busy. Here’s something from the “archive” though. Not sure why I never published these files before, but it looks like I didn’t and I really should – so here they are 😊

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Doubly pointless?

Yes, it is just another amplifier design I don’t really need, sorry. I picked up a set of PCBs from diyaudio not long ago because it is (yet another) medium-power solid-state amp that I want to try.
It’s called the FC100 and although the design is some years old now, I have seen quite few people describe it as a “secret gem” that sounds extraordinarily good for what it is. It uses On-Semi “ThermalTrak” transistors (NJLxxxx) with built-in bias compensation diodes and a few other “interesting” parts (= high-quality audio transistors). That in itself is not extraordinary, but overall it seems like a well-thought-out and well-executed design which for example uses a separate low-noise PSU for the front-end (on a separate PCB that I haven’t shown).

The boards are made by diyaudio member Rudi Ratlos and are from a previous group buy. There is/was a group buy of a slightly different version of the board designed by someone else, but I preferred this version, mostly because it was available immediately and also proven by many previous builds.
The only real justification for building this (beyond wanting to…) was that I have most of the active parts to hand already, and also that I stumbled upon some very cheap transformers – that are perfect for the main PSU in a dual-mono design – which helps keep costs reasonable (not “low” but “reasonable”…)
The title of the post actually refers to the fact that part of what I am working on right now (slowly, but surely) is to build a set – or two – of active loudspeakers. This wouldn’t just mean that building a power amp is pointless because I don’t need another one, but because with active speakers I wouldn’t need any power amps at all… 🙂

Still, I am as excited about finishing this and eventually listening to it as I am with everything else, but then as you probably know by now I’ve never claimed that I do DIY because it makes any sort of sense – it’s just a hobby 😀 

Project files: Headphone amp dummy-load…

Managed to source the last resistors this week, so I think it is about time to publish the files for this project 🙂

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Not just another headamp?

It seems that Neal over at Enjon.uk and I have been (unintentionally) ping-ponging posts over the last few months. He’s been building a few of my designs and I have been inspired to clone a couple of his 🙂

In one of these posts Neal mentioned that he built something that wasn’t “just another headamp”. I know what he really meant, but I couldn’t help but grab on to it. Not just because my latest build is “another headamp”, but also because it got me thinking a little…

As far as I am concerned, headphone amps more or less make the perfect audio DIY projects – especially if you are starting out in the hobby: There are tons of designs to choose from, you can get great – and very audible – results even with cheap circuits and unless you actively choose to venture into tubes or similar, avoiding high currents and dangerous voltages is relatively easy.

If you are a beginner, a student or just want to test whether audio diy is something for you it is also worth remembering that headphones are actually able to provide a level of sound quality that loudspeakers can’t really match at anywhere near the same budget. Back when I started this was a major driver, of course in addition to the fact that a headphone output on a preamp or integrated amp was not a given at all, let alone one that had decent sound quality or the ability to drive very low or very high-impedance headphones.

These days I certainly I don’t need these headphone amps for my personal use, but I still get tremendous enjoyment out of building (and sometimes designing) them. I honestly don’t fully know why, but I am pretty sure a large part of it is that when you turn them on for the first time and get sound it’s a much more tangible result than what I get from just about anything else I do (apart from cleaning the house and washing the dishes maybe 🙂 ).

So, back to today’s “offending article” 🙂 It is a headphone amp, but I definitely don’t think it would be fair to just call it “another headphone amp” – hence the title of this post. It is a Chinese clone of the Krell KSA5 design but with a few tweaks (so it might be more aptly described as a clone of a clone 🙂 ) I’ve done a few KSA5s on the “standard” Kevin Gilmore clone PCB and they work well and sound great, but I was still intrigued by this version. As far as I can see the amplifier circuit is untouched, but the protection circuit is different (based on a UPC1237 IC), the board is smaller and it uses a bigger heat sink profile.

The last point was actually more or less the decider because I thought it might make it possible to squeeze the board into a 1U case. As it turns out it might not be doable anyway because the heat sink profile isn’t completely standard so I couldn’t go down to 25mm tall heatsinks anyway but let’s see about that later. For now I’ll just take a few moments to enjoy that I have created something that gives a more “tangible” feeling of success than the meetings and powerpoints I have been spending the rest of my week on 🙂


So, the next episode in my Discrete Opamp adventures is an implementation of Bryston’s RIAA circuit based on the DOA33-modules. This is also a circuit that Bryston shows in their published pre-amp manuals and as you can see from the board pictures there aren’t really many components to it beyond the DOA-modules themselves (just like with regular opamps I guess…).

There is no DC-servo in the circuit and therefore it has coupling caps on all inputs and outputs. I’m sure that the coupling caps will scare some people off this design, but to me this isn’t a deal-breaker. The whole project is more about exploring the modular DOA-concept and less about building the ultimate reference RIAA anyway.

There are a couple of different versions of the schematic available from Bryston with only minor differences in parts values. I picked one and stuck with it, but my guess is that there are small audible difference to be explored if you want to. My component values are otherwise pretty much aligned with the schematic and the few exceptions (the input capacitance and the load capacitance) where the changes are either not significant (size of input cap) or improvements with my equipment (load capacitance).

Now, as you can probably glean from the pictures I haven’t actually made the four DOA modules that go on to the RIAA boards yet. However, I have been able to confirm that the board is working with the two modules I have on hand already and so up next is getting a quad of DOAs (probably the SMD-version this time) built up for a proper listening test 🙂