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 🙂

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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 🙂

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Project files: SDS/AMB headphone amp

The other half of my recent board shipment (see the previous post) was this design, which I’ve always liked but never tried. I can’t really remember what led me to start doing a PCB for it, but probably a combination of boredom and a flash of inspiration – at least that is what usually works 😀 Anyway, here is the design for anyone else who wants to have a go at it 🙂

Project files: Pascal I/O adapter

After a longer-than-expected delay in shipping, I received some boards. Among them was the revised version of my Pascal adapter board, so after a quick check that it still works, time to release it into the wild… 🙂

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 🙂

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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…

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ICEmatch-modules…

It’s getting harder and harder to find ICEpower modules I haven’t yet tried, but here is one – the “ICEmatch” amplifier and PSU combo.

Developed as a modular solution for multi-channel and custom-install applications, each 80AM2 amplifier board can be two-channel stereo or BTL mono, while the separate PSU can power up to eight amp boards (= 16 channels).

I grabbed the set (one PSU and two amps) from a local classifieds listing because they happen to match a project I am planning (or should I say “contemplating”) – a sort of large-ish bluetooth-speaker kind of thing for a bedroom or an office (although probably without bluetooth – don’t need that!).

They USP of the ICEmatch boards compared to the normal modules is that the two amp boards I got can be configured into a 2.1 amplifier with a bridged channel for a “subwoofer”, which is exactly what I want here. Also, the PSU is well-equipped with aux. voltages for control and input boards which I expect to need.

This is definitely a long-term project because not only do I need to figure out a front-end for the amplifier, meaning an active filter circuit of some sort, but I also expect I’ll need to lay out a couple of adapter boards for the wiring and work on a lot of other things (the acoustics, for one).

I am quite confident the modules will be good enough for this project and sound quality isn’t the ultimate priority as such, but I might have to rig up a test set up and try them out first nonetheless… 😀

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! 🙂

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 😀

Project files: LME49600-based headphone amp

When I built the LT1210-based preamp I thought I set a record for longest wait between making a PCB and actually trying it out. I am happy to say that the record has been broken with this – a headphone amp based on the LME49600 buffer IC, which I apparently did back in 2013 but haven’t managed to assemble and test until now (!).