A super gainclone…

Does the world need another Gainclone-type amplifier? Probably not, and I certainly don’t either. However, here’s one I managed to overlook until very recently, and it is called – rather immodestly – the “Super Gainclone” 🙂

It’s designed by Bob Cordell (who does know a thing or two about amplifiers it has to be said) and it comes from one of his books. It was “launched” on diyaudio with this thread and I’ve somehow managed to completely miss both the design and the associated PCB group buys until a few months ago when someone was offloading a few excess boards which I purchased.

The circuit is based on the LM3886 IC (more or less the only one of these ICs still in production) and it isn’t really a “barebones” circuit as is often the case with GCs. Instead, it incorporates an input buffer, a DC-servo and an optional soft-clipper circuit (called “klever klipper”). Cordell has also retained the general “best practice” decoupling and stability parts (e.g. the output LC) that often get left out by overzealeous DIY’ers who thinks that these are not needed or even compromising the sound quality. However, unlike many other of the more “complicated” GC designs this isn’t a “composite” amplifier (where the input opamp provides a lot of the gain), so maybe there is room in the world for one more GC variant after all?

The board layout was done by Mark Johnson on diyaudio and it is very good, but also look nothing like I would have done them and some of the footprints are definitely not ones I would have used – that’s a minor thing though. Along with the amplifier PCB layout, Mark developed a matching PSU as well. It’s a pretty simple design but it should work just fine for this application. I do hate the upright (“tombstoned”) resistors, but it’s not exactly the end of the world, is it?

The reason for the blank capacitor positions is that I have no case design for this one yet so I don’t want to make a choice on caps already now. Similarly, trimming the clipping circuit takes a bit of time and as mentioned I don’t really have a case idea yet, so I’ll save that for later. However, after a string of builds that either didn’t behave as expected or plainly didn’t work, just getting something together that actually powered up as it should feels as a “win” right now 🙂

Fully activated?

My speaker projects are hibernating a little at the moment – mostly because woodworking outside isn’t really possible in the current sub-zero temparatures – but once the weather improves I am definitely starting up work again.

However, the one thing I dread a little about speakerbuilding is to have to design crossovers (more or less) from scratch. Not because it’s complicated as such (I am quite happy experimenting and doing “trial and error”), but because there are tons of variables and takes time before you get through all the different variations and find something that’s really listenable. All the more reason to keep an eye out for good offers on something that makes life simpler then…

As I think I mentioned in the past I actually bought a pair of MiniDSP PWR-ICE plateamps but stupidly sold them on again because I didn’t think I would ever get around to using them. I still regret that, so when a pair of lightly used Hypex Fusion FA122’s popped up at a decent price on my local classifieds page last week I jumped on them. My previous experiences with the NCore amps show that they are very capable, and this time I am sure I will eventually use them 🙂

The somewhat improvised casing and mounting system (yep, thin plywood and electrical tape!) is not mine, but comes courtesy of the previous owner who used the amps in a test/prototyping setup. While it’s a bit of an eyesore it works well, so at least for now it is not going anywhere. If the amps are eventually going to mounted on the back of a pair of my DIY speakers a few scratches and tapemarks aren’t going to matter and it’s actually a very flexible solution for prototyping.

A more practical problem though: As a committed Mac-user I don’t actually own a Windows-PC which is required to run the Hypex software, so while my woodworking activities are on hold I need to get started on fixing that problem – preferably cheaply 🙂

Starting a JC-80 clone…

As some regular readers will probably know, the fact that I have been doing DIY audio for a long time now means that I do have some “exotic” parts left from the times where audio-grade parts were more readily available than they are today. I suppose I could just try to sell off these parts at ridiculously inflated prices, but as the reason I originally bought them was that I wanted to build stuff I generally I try to do that instead.

During one of my (countless) online searches I found a discussion about this clone of the JC-80 preamp (original schematic here) and that piqued my interest. The design uses the well-known (but now exceedingly rare) 2SJ109/2SK389 dual-JFETs for the input stage. I have a couple of pairs of those left over that I have been thinking about using for something and this design seemed like a good candidate. Apart from being discrete and balanced – both big positives in my book – the design has one other unique “selling point”, namely that John Curl apparently has stated that it’s the best preamp circuit he’s ever designed. That meant I ended up deciding I wanted to give it a go (even if it’s maybe just “one of the best” 😀 ).

The boards I used are from jimsaudio (also on ebay). My original plan was actually to design my own board because I was not that impressed with the layout of this one from looking at the pictures. However, since it is very much a “dead-end” design with obsoleted parts I decided not to bother with an own redesign and ordered a ready-made pair of boards instead. It seems like COVID-19 hasn’t fully loosened its grip on global postage though – I ordered these boards in the beginning of December and it’s barely a week since they arrived.

When I got the boards I warmed a little – they are 2mm thick, gold-plated and with 2 oz copper (which you can clearly feel when soldering) and generally of very high quality, so at least that’s something. On the other hand they do have some idiosyncratic touches that are very common with these Chinese designs – not sure why. The small caps have a 7.5mm pin spacing for no obvious reason – 5mm would have been much more common. Likewise, the large axial caps are just supply decoupling and could easily be a smaller box-type footprint and so on. All in all these are minor issues, but the do seem to be entirely avoidable to me.

As you can see I have nearly finished putting the boards together. The power dissipation of the JC80 is around 20W per channel so heat sinks are definitely required and just mounting the boards to the bottom of a case doesn’t seem to be enough to keep a finished amp cool. Instead I found a suitably large angle profile on ebay that I can use for mounting brackets and which has also just arrived. Unfortunately the seller didn’t cut it to my specs as instructed so I have to do that myself, leaving me with a bit more mechanical work than I originally anticipated here.

Assuming the boards work as they are (and hopefully they do) that then means I can start looking at case designs and think about how to eventually test the claim that this is the best John Curl design ever 🙂

Low-hanging fruits…

Since my X-mas break I have been doing a little clean-up in the house – it’s been three years since I moved and so I guess it is about time to unpack and go through the last boxes 😉

However, in all honesty most of the cleanup I need to do in the house is related to half-finished audio projects of various kinds I have standing around. I haven’t done a lot on that front lately, but one of the things I noticed is that some of these projects stopped for very little reason – and actually don’t need a lot of work to be finished.

One of the builds I found was a Krell KSA5 clone that only really needs a bit of wiring. I remember why I left it (because I wasn’t sure that it was biasing up correctly) but that doesn’t seem to be the case now – need to test a bit longer though.

I also don’t think I have posted about the KSA5 design before, which is definitely an oversight. The KSA5 clone was done back in 2012 by Kevin Gilmore based on the original Krell PCB. To accompany the amplifier Kevin made a couple of PSU boards as well, one for the original Krell layout and one for a slightly improved version. Both of them are discrete regulators based on zener diodes and power transistors.

For this build though, I went for a pretty simple PSU based on two IRM modules and a filter board to be able to squeeze it into a smaller enclosure (basically a precursor to the integrated boards shown here). I have another KSA5 (might actually be two…) PCB in a full-size case that I also need to get to at some point, and the full-size case means there is space for one of Kevin’s linear PSUs instead.

There have been few board group buys over the years and you can still get KSA5 PCBs on ebay based on Kevin’s original Gerber files as well. You can however also find some cheaper chinese clones that are not completely identical – I suggest you stick to Kevin’s original layout to be sure.

According to Kevin the KSA5 shines with low-impedance headphones and that should actually be fine for me. When I do listen to headphones (and it is exceedingly rare these days) it’s mostly the 36-ohm AKG K812s that I reach for, so that seems a good fit.

I really should get that bit of wiring done soon… 🙂

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 🙂

Happy New Year!

As we close the door on 2020 it’s hard not to think about what an extraordinary year this has been…

2020 has been a challenging year for a lot of people. Going into 2020 I doubt that anyone (at least in my part of the world) had really expected what would happen during February/March – or that we would be back to the same situation once again now.

Audio-wise for me it’s been a bit of a funny year. The first lockdown-period in the spring actually meant I had a bit more spare time than usual and I got a lot of stuff done. However, as spring gave way to summer I had long periods of not really doing anything audio-related because the weather was nice and other activties beckoned. In the autumn I sort of “eased” into a second period of purely working from home, but it still took a good while to adjust.

Biggest surprise of the year in relation to the blog is probably how much people seemed to notice my “manifesto” of thoughts on diy audio and cooking. Considering I almost scrapped the post draft because I thought it was a bit too stupid I think the response has been great. Other than that, during Decemeber I’ve passed 300 posts and also 1000 total comments – some of which aren’t even my own (or pingbacks)!

Being at home for much more of the week than usual has meant I have spent more time actually listening to music at home, so I have been able to test some of my builds in a more realistic setting which is quite nice. However, it also confirms how much I tend to think “well that sounds pretty good” unless I really concentrate and listen for differences between different components. I can’t really decide if that is a blessing or a curse, but probably mostly the former – being able to simply “enjoy the music” without obsessing over the sound quality is often a good thing I think…

2020 was also the year where I (sort of) started doing loudspeaker projects again and hopefully I’ll be able to make use of the remaining winter months to finish something here. Right now I do miss being able to do the most messy parts of woodworking outside, but as that isn’t really affected by COVID-19 but only by the miserable Danish winter weather at least that problem should resolve itself in a few months 🙂

As I’ve written previously the 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 an improvement in 2021, so that we can move on without (necessarily) blindly going back to where we came from.

So even if we’re not completely out of the woods yet, here’s to a great 2021!

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? 🙂

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 🙂

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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… 🙂

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