An original clone?

Something of an oxymoron perhaps, but this NCC-200 amp from Avondale Audio probably qualifies as “the original” Naim amplifier clone.

Naim clone amplifiers are plentiful these days but somehow nearly all of them seem to reference the Avondale schematics. Some people also started tweaking the design (with varying degrees of success it must be said…) and the NCC200 also inspired the “HackerNAP” design – although in this case you have to look a bit harder to even see the similarities 😉

To be honest it’s not hard to see why these amps would be a popular subject for DIY clones. The older Naim amplifiers are fairly simple discrete designs, they sound good and they fit a DIY’ers “modular mindset” quite well. Many of the different commercial Naim amplifiers were not actually different amplifiers, just the same amplifier board with a few tweaks and then different rail voltages and PSU/chassis combinations to make both mono and stereo amps in various power and quality levels.

Before Xmas I spotted that Les (the man behind Avondale Audio) was selling his last NCC200 boards on ebay and after a bit of consideration (I don’t really need more amps after all) I decided to buy some boards. With such a variety of clones there are obviously numerous cheaper ebay options available for boards but that wasn’t really the point here – I wanted to try “the originals”.

I was honestly planning to show this build in slightly more completed form, but gave up on that when I suddenly realised that I didn’t have the MJ15003 output transistors in stock anyway (they are now in the mail somewhere). The NCC200 has what’s called a “quasi-complementary” output stage, meaning it uses two NPN output transistors per side rather than an NPN/PNP pair. Which obviously means you need four (4!) transistors for a stereo amplifier and that is apparently more than I can count to at the moment…

For the power supply I think I’ll go with a “barebones” configuration of just a single PSU for the whole amplifier instead of separate PSUs for the front end and output stage. I have a few PSU board designs already – not least my “HackerCAP”-clone – that could be used, so that part I am not too concerned about.

In the stock form this is quite a low-bias amp and so it can get by with limited heatsinking. As I have a pair of small boxes from ebay already I plan to make these into a pair of small mono blocks. Apart from missing some suitable transformers I just need to shoehorn all the parts into the boxes. It looks doable though, so once the missing parts arrive I can start working out how to do that 🙂

Locked in – again!

With the Christmas break on the horizon the Danish government like many others this week announced new Covid-restrictions for the next few weeks which effectively amount to another lockdown. So even if some things are the same this year (the pre-holiday panic at my work for one…) then it looks like some things are going to be very different indeed.

My traditional new year’s travel is of course off and it does mean some other activities will not be possible, but I am immensely lucky that it is really just an inconvenience and nothing more so I really shouldn’t complain (and I’m not). Travel has been out of the question for a while anyway and so I was planning to spend my time off building some audio projects. And now, with most other options closed down I should have a good opportunity to make progress.

Pre-holiday panic aside, one thing I’ve managed to move along in the last few weeks is this little power amp, based on my PA-100 gainclone prototypes:

Normally I dread casing stuff but this is one build I have really wanted to finish for a while so I can listen to it and compare it to some of the class D designs I’m using. I’ve meant to start building for some time now, but a bit of cleanup recently uncovered a suitable case and a matching switching PSU from Connex and then there really were no excuses left for not getting started between a raft of Teams-meetings over the last weeks.

The reason I don’t always like casing stuff is that it often you have to drill holes that line up exactly in order to get everything to fit, it has to be assembled in a specific order etc. and overall it’s just one big 4-dimensional puzzle in time and space 😀 It’s immensely frustrating to do when there are problems or you get something wrong, but of course also equally satisfying when it works out in the end – and so far this has worked out as I expected it to.

We’re not quite there yet though, because while I’ve submitted a small “pre-christmas” order of rear panels from Schaffer this design did not make it so it will have to wait for early next year, but I can do just about everything else on cabling etc. in the mean time.

Happy Christmas, and I hope that the holidays bring (at least for a while) a little light onto whatever darkness you might face right now 🙂

A well-balanced preamp…

Another intriguing (and completely unnecessary…) preamp design is this one. As you can see it is pretty compact and two-in/one-out balanced with onboard XLR-connectors.

The design is by Bruno Putzeys (of Hypex/Grimm/Purifi fame) and it’s discussed and explained in this article. To be honest I’ve read the theory a few times and I’m still not sure I get it, but with Bruno’s credentials it’s not a big leap of faith to imagine that it’s something worth trying 🙂

I’ve noticed this design – usually called the BPBP (= Bruno Putzey’s Balanced Pre) – in the past, especially as there have been a few board group buys before, but for some reason I didn’t bite when I had the opportunity. However, I recently spotted a board for sale with SMD-parts populated (also a group buy offer on at least one occasion) and since this was what I wanted I grabbed it.

Obviously having the SMD parts populated meant there wasn’t much work do but sometimes it’s also nice to do something that is straightforward. I also managed to find a pre-made rear panel layout file, so even that part is expected to be quite easy 🙂

As my board came with the SMD-parts pre-populated the opamps are the default LM4562/LME49720, while the regulators are (perhaps not surprisingly) the low-noise Hypex HxR12. I bought a cheap pair of these regulators at some point so when I finally got my hands on a pre-board it was obvious to use them here.

The two on-board inputs are relay-switchable which is really great – it means that this pre is much more likely to find a place in a permanent system at some point when it’s done.

The offboard volume pot is implemented a gain control for one of the amplifier stages. The good parts of this choice are highlighted in the article – you can use a linear pot which typically has better tracking and even for the balanced amp you only need two decks, meaning that it doesn’t impact channel matching in the same way as a 4-channel pot.

The downside for me is that the volume pot is part of the feedback loop and ideally there should be no wires to it. However, the board-mounted pot is too much of a compromise for me so (once it arrives) I’ll be starting out with an Alps Blue on short wires and then possibly look into DIY’ing something else based on one of the relay-based designs available.

Once the volume pot is here I’ll try out the preamp in a more “realistic” setting than the bench, but I do expect it to sound quite good. It will also be interesting to try out if there are any specific synergies when paired with the another Hypex amp – who knows? 🙂

Local finds…

My local classifieds site is not generally awash with interesting diy audio offers, but it still pays to keep an eye out. On a couple of previous occasions I’ve picked up ICEpower modules at good prices and last week I spotted something else that caught my eye.

It is a pair of amplifier modules based on the (no longer available) LME49830 driver IC. What specifically caught my eye was firstly the “all-in-one” design with an output relay and secondly the asking price – just under 35 EUR for the pair. It goes without saying that I don’t need any more amplifiers, but since they were cheap and available for pickup within 15mins from where I live I thought that made them “worth a punt” as they say 🙂

The LME49830 (and its siblings, the LME49810 and LME49811) were/are integrated driver ICs that attempted to take the pain out of driving a good driver stage and just had to be mated with a suitable output stage – MOS-FETs for the LME49830 and BJTs for the LME4981x variants.

As the drivers were able to tolerate up to 200V supplies, you could build very high power amps as long as the output stage, the PSU and the heatsinking were up to the job. The LME49830 did get some good reviews in its day and was included in some commercial amps as well. That said, I imagine that with the advent of class D they became a sort of “stuck in the middle” value proposition – not quite as compact and as efficient as class D for the mass-market, and not quite as “posh” and “pure” as fully-discrete class AB for the enthusiasts.

From the published schematic my board actually looks fine. I haven’t been through the schematic in detail, but I would expect that it is closely based on TI’s AN-1850 application note with the addition of a standard UPC1237-based speaker protection circuit. The only thing that stands out to me is that the recommended supply voltage of +/- 55V seems a bit much for a single pair of transistors, so maybe that needs to be reduced a little? (I’ll read the datasheet and app. note a little more carefully before deciding that one).

At first thought the obvious companion for there relatively compact boards would be a (similarly cheap) switching PSU. That would make for a very compact, and probably still very capable, amplifier. However, I should probably I’ll dig a little in the transformer collection first though – I probably already have something that would work for a linear PSU 🙂

Thoughts on DIY audio and cooking…

This isn’t really a “manifesto” (even though it might read like it in part…) but more some reflections on DIY audio in general. It should also serve as a bit of a guidance to how I think about DIY and thus some “context” for how I design and how I answer questions about parts choices etc.

At the core of this thinking is a simple analogy, namely that to cook a delicious meal – or build a good sounding audio circuit – you fundamentally need three parts:

  • A good recipe (= schematic)
  • Some good ingredients (= parts)
  • Careful preparation/execution (= board layout, wiring etc.)

The three parts are obviously interrelated, so it should be obvious that the first important lesson is that mindlessly pursuing improvements on one of these parameters while ignoring the others is stupid, because you’ll just hit another barrier for performance. Small improvements are of course fine, but real impact comes from holistic thinking.

OK, so what else does this tell us with respect to DIY audio you might ask? Well, I would say:

  • Just as it is possible to use only the most luxurious ingredients to make something that is totally inedible, it is possible to get something very tasty out of “mediocre” (or more accurately “pedestrian”) ingredients. How this applies to expensive/exotic/premium/audiophile parts is hopefully obvious to everyone… :).
  • Experimenting with changing (= “improving”) designs is fine, but you need to know what you are doing and what the original “designer” was aiming for before you are able to genuinely say you’ve improved something. Saying you believe it “tastes better” is just fine, but just be aware that others might not agree with you.
  • The preparation/execution part is a bit tricky, because while some ingredients/recipes (= parts/designs) are very tolerant of substandard execution, others are definitely not. Low-frequency analog is generally easy to work with, but it is perfectly possible to ruin an otherwise brilliant circuit for a class D amplifier with a poor board layout, or make a great RIAA-design all but unusable with shoddy wiring that causes a lot of hum and noise.
  • An interesting twist on this is that expensive parts can in fact be less tolerant and not more (e.g. expensive fast opamps will be more likely to oscillate, better and faster audio transistors will be more likely to cause instability, expensive audio-grade caps are less tolerant of high heat and high ripple currents etc.). The upshot of this is that mindlessly pursuing the “greatest” parts isn’t just expensive – it’s actually stupid and in some cases counterproductive. Unless you know what you are doing and understand how the other two levers affect the circuit you are working on, your “improvements” might actually be worse.

Now these three “ingredients” are the foundation, but there is still a “fourth ingredient” that should be reckoned with. This is the menu composition (= system synergy) where your impression of a single dish is influenced by what you are otherwise consuming with it. If you follow my writings here you’ll know that this is a recurring theme that I write about and for me it goes a long way to explain individual sound preferences that aren’t necessarily shared by all (without going to the obvious conclusion of just outright personal taste).

I’m aware that some might find this controversial, but to anyone who disagrees with me can I just challenge you to buy two expensive and (individually) delicious dishes at random and think you are guaranteed a good result – oysters & hot chocolate anyone? 😀

I am sure there are areas where the analogy doesn’t hold completely – and I am definitely not enough of a cook to verify all this in practice for myself 😀 – but I think it is still a good analogy and hopefully it makes some sense as a point of reference for readers here 🙂

More PeeCeeBees…

After a bit of waiting for the postman to show up I now have a couple of new projects to look forward to…

As the title alludes to, it’s a preamp in the “PeeCeeBee” series developed by diyaudio user “Shaan” where I’ve previously showed the small power amp design called the V4.

“What’s another discrete preamp” you might ask, but Shaan’s circuits are normally very well thought-out and solidly designed, so that alone makes the design interesting I think. The second thing that makes it interesting is that the “PCB-pre” allows adjustment of the feedback between the preamp stages via a potentiometer that can be front-panel mounted. This means that it is possible to adjust the amount of harmonic distortion the preamp adds which directly affects the sound signature.

Considering how much emphasis I usually place on system synergy I think this will be a good opportunity to put some of those thoughts to the test, because if the system matching doesn’t matter then I should prefer a specific setting regardless of the partnering electronics, right? 🙂

Anyway, even with the best will in the world I will certainly not be the first one to finish building the pre because I am short some parts that I need to order. Also I can see that Neal over at enjon.uk received his boards so far ahead of mine that I can’t really beat him to making a finished amp 😀

Also included in my shipment were a couple of PCBs for the V4H rev. 2 power amplifier. The V4H is the “bigger brother” of the original V4 with two pairs of output devices per side, but otherwise identical in design and topology. I did actually buy the original V4H PCBs and I was starting to working on them around the time when the preamp group buy was announced. However, when I discovered that the design was being updated to v2 I decided to wait a little and get a pair of those boards instead.

Like the original V4, the V4H is built around bipolar transistors for input and VAS stages, and then Exicon/Hitachi lateral MOS-FETs in the output. This is normally something of a “winning recipe” in amp design and I am looking forward to hearing what a “normal” class AB design can deliver compared to the class D offerings from ICEpower and Hypex that I have been getting used to over the last months…

A pair of Dynahis…

The summer is now firmly on the retreat here, and as the weather cools down and the days get shorter it also becomes more natural to stay inside and build stuff – time to dive into the project pile and finish some builds then! 🙂

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Powering up the Pascal-amp…

I am always amazed by how a project can seem impossible to get started on for a very long time, and then suddenly one day the solution is there and the work of realising it is only a few hours.

One such example was when I bought a Pascal S-Pro2 amplifier module last year. As mentioned in the original post I wanted to create a breakout adapter board for the Pascal’s 26-pin IDC-connector which isn’t the most user-friendly connector around. I’ve actually opened the board layout on several occasions but I really couldn’t crack how to get a good start on it.

In this case it was simply working on a different PCB design (which I expect to show shortly) that suddenly provided the flash of inspiration I needed. The realisation was that I could put the connector for the Pascal board in the middle of the breakout board and then arrange the breakout connectors pins all around it – not exactly rocket science, but there you go.

I’ve just done a brief test on the adapter board and it seems to work well – it is certainly easier to use than the IDC. I will of course be publishing the boards files for this one but it’s going to be some time because it does need a little rework first.

Problem number one is that I’d sort of forgotten that a double-row connector isn’t fully symmetrical so you can’t put it on the bottom if it is placed on top in the layout. Problem number two is that the connector really should be a polarised box-header to match the IDC connector and there’s barely enough space for that. However, the current incarnation of the board seems to work and that at least means I can listen to the Pascal module in raw format and also start thinking about a case layout for it – let’s hope the inspiration for that one comes a bit sooner 😀

Tools of the trade? (part 2)

A bit later than expected, but here is the second part of my “Tools” overview posts (the first part is here). This time the focus is on hand tools and other smaller “helpers”.

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Soulmates?

A while ago I showed one of the results of my decision to restart buying speaker parts – a pair of Scan-Speak Illuminator midwoofers – and a few weeks ago I managed to get my hands on a pair of tweeters to match.

My original plan with this project was to build a version of Troels Gravesen’s Illumina-66 design with the Scan-Speak R3004 ringradiator tweeters. I had actually designed an enclosure plan with the right 5 degree tilt and started cutting up the MDF for it, but mid-project I sort of changed my mind. Fundamentally the reason I want to build another pair of speakers is not because I need them, but because I want to experiment with them and see how good I can make them sound (possibly even with DSP/active filtering at some point). So, instead of just ordering the ring radiators I decided to wait a little and see if I could find something else that was more “interesting”…

After some weeks of waiting I spotted a pair of very slightly used Mundorf AMTs (the closed-back 25 model) on a forum and decided to pick them up instead. They were about the same price as a new pair of R3004s and I have heard good things about the Mundorf AMTs. Also from past experience with my AMT-based Elac speakers I tend to like the sound “character” so I thought it was worth a shot. I was a little unsure about achieving good matching between the larger AMT and the woofer, but it looks doable to get a good result (even without DSP).

As my original enclosure plan had to be scrapped I have yet more wood to cut up before I can proceed with the build. Woodworking outdoors is still much easier than indoors so I will need to take advantage of gaps in the rain over the next few weeks to get that done 🙂 I’m going to keep the basic reflex tuning of the Illumina-66 because Troels probably knows more about this than I do, but I can change the overall cabinet design a little bit to suit my need since I’ll need to redo the crossover from scratch anyway.

Timeline for the project? Don’t bother asking… 😀