Finishing touches…

So, like most people these days (at least the ones with office jobs I guess…) I have been at home for the past week due to the COVID-19 restrictions. Apart from more online meetings than I really wanted it’s been OK. I am not sick and to be honest given my circumstances at the moment I am about the last person who should complain about this situation – so I try not to :D.

Another reason why it’s not all doom and gloom (at least not yet) is because being asked to stay indoors as much as possible means I’ve had time to finish up some of my half-finished projects. I’ll be posting these over the next weeks (and hopefully add more to the pile in the mean time) 🙂

First up is an eBay-clone of the Naim NAC152 preamplifier (originally shown here). I had halfway cased this up a while ago, but I decided to make some changes to the front panel layout plus add a matching PSU. The obvious PSU choice was a STEPS which I fortunately had nearly all of the parts for already. I also had a chance to look at the PCB layout for the STEPS and revise it a little, so if you keep an eye on the project file page I’ll add a revision 1.5 board file in a few days. It’s not major changes, but when you’ve been away from a design for some time there are always things you want to improve which you could not see the first time round.

The “Naim” preamp was promising enough on first listen that I decided to put it in a simple case. The cases are from Modushop and they have a nice profile I think. The only thing I haven’t done is splurge on thick customised front panels, but that’s not really necessary anyway. I added a second output on the PSU because I have quite a lot of other preamps designs that run on 24VDC so this way I can keep a single PSU and switch between them.

Soundwise I’ll be trying this out “for real” in my main system as soon as I hopefully manage to fix an intermittent connection in one of the speakers – it has been bothering me for a while but as I now use the speakers daily now is the time to (finally) do something about it 😀

MQ preamp…

Yet another ebay-purchase, partly to feed the shopping habit and partly as an excuse for some relaxation with the soldering iron :D.  This one is a ”cousin” of the BP26 project as it was made by the same people who designed that board.

It is a discrete preamp circuit with a discrete regulator PSU, an output delay circuit and a four-input relay selector on the board as well. It’s (supposedly) based on an (unspecified) Mark Levinson circuit design, although I usually take these things with more than a grain of salt. If nothing else because there are usually component replacements and tweaks to the original schematic, but sometimes even the basic topology deviates from the original. Anyway, I thought the board looked interesting and as I already had some of the more expensive parts I could keep the initial investment on a reasonable level.

Apart from the somewhat questionable ethics of cloning and selling brand-name circuits I have to commend the ”designer” of these boards, because they are good quality, they seem well thought-out and they are delivered with full documentation. I’ve actually received less comprehensive information with commercial boards and both of these boards have gone together without any problems and worked the first time they were powered up. The confidence that I am going to be able to put something together without too much trouble actually weighs more and more when I decide to buy something, because I dislike troubleshooting and always end up leaving non-working projects for far too long, so going forward I am going to keep this in mind (is “buildability” even a word? 🙂 ).

As I did with the BP26 I’ll try to listen a little bit to the amp first before deciding how much to splash out on the mechanicals, but impatience may get the best of me still. The missing transformer is already in the mail though…

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 🙂

Naim the clone…

Yes, sorry for that terrible headline 😉 One of the ebay-kits I mentioned I my last post is this one.

It’s (supposedly) a clone of the Naim NAC152XS preamp. Now, I’ve not spent a lot of time working out the circuit details (a bit of information available here), but apparently it consists of a simple gain stage and an active filter which also serves as a buffer (and a volume pot in between). It could well be that this is a somewhat bastardised version of the original Naim circuits, but that’s not terrible important for me.

Although part of what made this kit interesting to try was that Naim is one of those hifi-brands that have a distinct sound signature – and a loyal following because of that (some would undoubtedly claim that you definitely don’t buy Naim gear for the looks so it has to sound good… 😀 ). What really caught my eye was that it is a very simple discrete circuit and it is single-supply. Discrete is always fun and while single supply circuits do have some drawbacks (additional capacitors in the signal path etc.), they also have some advantages for DIY’ers. One large advantage is that the single supply rail is normally easier to make and certainly easier to transfer between boxes, so an external PSU suddenly becomes a more viable/desirable option – and that’s where this will go as well when I get that far.

My contribution to this project – apart from soldering all the parts in the right places – consisted of replacing the capacitors in the signal path with Nichicon ES bipolars which are a bit better suited to the job (and nice and green!), and then just matching the supplied transistors as good as I could to make two identical channels. I also supplied the four board-mounted RCA connectors which I had left over – and then immediately after soldering them in place I remembered I had actually put them aside for another project 😉

Now, as usual I don’t post detailed impressions of the sound quality (mainly because I don’t have any right now), but my initial impressions are definitely positive enough that I’ll go forward with finding a suitable enclosure for these boards because I think they deserve that 🙂

More Naim clones…

Yep, I know I should be working on the HackerNAP instead, but I was just in the mood for building something else and as I had another Naim clone kit lying around, here we are 🙂

This is a NAP140 clone (or one of many actually) from ebay. I bought a cheap kit thinking I could get away with just replacing a few caps as usual, but I actually ended up replacing most of the resistors as well after a couple of them tested out of tolerance – hmm…

Also, while the listing said the 2SC2922 output transistors would be genuine after checking them I’m fairly certain they are not – at least the screen print looks wrong. The PCB is also much flimsier than usual, so actually this is one cheap kit I wouldn’t recommend that you buy 😦

Anyway, I know a couple of places that have genuine Sankens at a reasonable cost, so with a few of those and the last few caps (already on my next Mouser-order) then we’ll see if this one powers up 🙂