Harmonic experiments…

Not much to say about this one really – I finished casing my build of the Korg Nutube B1 preamp (as shown originally here). By using a built-in power supply based on a filtered IRM power module I managed to keep the unit compact and still avoid the external PSU which I quite like.

I’ve only done very quick listening tests with the amp, but considering how varied opinions I have read on the sound quality I am positively surprised. The post title is obviously in reference to the fact that it is possible to “tune” the profile of harmonic distortion that the amp produces which I haven’t really tried, but I actually would like to try it and get a sense of where my personal preferences lie.

I am also positively surprised that the amp does not seem to have a big turn-on/turn-off thump (as I have seen some people mention). Not sure why (maybe it’s the PSU?), but it definitely makes it more likely that I will actually use it in my system where “livability” is a major factor (even if it’s not an actual word…). Maybe I should do a “second generation” of my original B1-based office system?

A new king?

Normally I spend a surprisingly low amount of time listening to the builds I finish, but this one is an exception. That’s because I finished casing my Hypex NC502MP class D module and as I have very little experience with the Hypex class D amps, I had to try it out.

The original plan for the module was to build a top-end “integrated” amplifier but I quickly abandoned that idea (however, I picked it up again later with this build). Instead I’ve simply cased the module in a basic Modushop case but added an 8mm thick piece of aluminium to the bottom. A small niggle is that I can’t seem to find the crimps for the signal connectors so I used the cables I had to get the amp working, but it would be nice to be able to put in a functioning mute switch and a power LED as well.

As you probably already know class D is very efficient and class D amps therefore run very cool – right? Not quite actually. The very high efficiency numbers are always measured at (nearly) full power and at low power the efficiency is typically quite unspectacular. The Hypex module here has idle losses of around 20W, which honestly isn’t far off what you might get from an 80-100W class AB amp with a traditional power supply.

The module does therefore run quite hot and don’t for a moment think that my “thermal design” here is suitable for anything except a limited home use application. Even so, it’s hotter than I expected and what surprises me most is actually that I measure very high temperatures on places like the output chokes – these parts are not heat sinked to the backplate and so presumably a better heat sink on the back would not make much difference?. In any case the few experiments I did were enough to break with my conventions and order a ventilated lid for the amplifier instead of the usual one I use, because running the amp “topless” did make a difference to the temperature of the board.

On to the listening then: The logical comparison is against my “new favourite” ICEpower amp, the 700AS2. However, initially I just hooked up the Hypex amp to my test speakers (a pair of 5” Tang Band full range drivers in small reflex boxes) and even then it was obvious that this is a high quality amp. I especially noticed that the small TBs actually managed to sound like they had some bass articulation, which definitely isn’t common. In fact, the very improvised “test setup” ended up staying on my temporary work-from-home desk for three days of near-field listening.

Moving the amp into the main system and the positive impressions continue – this really is a great-sounding amplifier. To make a long story short though, I still ended up returning to the ICEpower amp in my current system for two main reasons: One is that the ICEpower amp seems to give a slightly wider soundstage which I am honestly a bit of a sucker for, and the other is that the ICEpower seems a little leaner in the bass. Whether that is a good thing or a bad thing in absolute terms I am not sure about, but my speakers are quite bass-heavy already and any more just makes them boomy which I don’t like.

Be in no doubt that to me this is a very capable amp though, and as I have a suitable enclosure with a bit more heat sinking that would suit a dual-mono setup I’ll definitely be keeping an eye out for a pair of the mono NC500MPs 🙂

More progress…

So, here is this week’s completed projects! (I honestly don’t think I’ve ever been able to write that before, but as promised earlier I got some new rear panels so I was able to keep up the pace 🙂 )

I’ve manage to case and complete both the NE headphone amp and the ACP+ prototype boards and again – the time elapsed between completing the PCBs and actually being able to close the lid on the completed build has to be a new record for me 🙂

For the ACP+ I have obviously made both headphone and preamp outputs despite choosing a fairly small case (and it only just fits). Now, I don’t think the wiring on this one is going to win me any prizes (nor, I expect, is the slightly OTT chrome-plated volume knob…) but that doesn’t really matter now because it works well and it is undoubtedly a cracking amp – whether used as a headamp or a preamp.

For the NE-amp I only had the headphone output to worry about, but I still ended up upsizing the case a little bit because it simply looked and worked much better. Power supply is one of my filtered IRMs and that seems to work well. Again, I am a bit surprised that this old design can turn into such a well-behaved amplifier. Pretty stupid of me to wait so long to start building it 😉

Completing the “set” we have a Whammy-amp, namely the official board I bought and showed here. This build was supposed to be one of the easiest because of the all-in-one board, but actually turned out to be one of the most annoying I have done for a while. I managed to measure up the front panel incorrectly not just once, but twice (!). First I couldn’t fit the headphone jack and having fixed that I then found I could not close the case because of the tall heat sinks. It seems complacency is indeed a dangerous enemy… Either way, it’s now done and working 🙂

Unfounded liabilities…

The title of this post was the title of a thread on a forum I used to spend time on years ago. The forum was about (smart) men’s clothing and the thread was a place to show off the fabric that people bought (cheaply) and then planned to have turned into custom clothing pieces (often at great expense) later on. Many of these expensive plans obviously never came to fruition, but that did not seem to do much to discourage people from buying more cloth.

My satorial ambitions are a bit lower these days, but the concept of “unfounded liabilities” pretty well sums up my ability to buy loudspeaker parts that I am not really sure I’ll ever be able to use. I had managed to kick the habit when I still lived in my apartment because I finally realised that it was a futile exercise – there was simply no room for more loudspeakers and I did not have the tools or the space for speaker DIY anyway. However, as I now live in a house and have managed to acquire (a ton of) tools maybe it’s time to start again…?

My first project (and I actually bought those drivers a few months ago because they were very cheap) is a pair of closed-box bass modules to be useable as speaker stands. The plan was (is) then to supplement the bass boxes with a smaller two-way speaker to make a complete, yet fairly flexible, speaker system. I have a few design criteria for the “tops”, e.g. I’m happy experimenting with the crossover but I want to start from a working enclosure plan, I want to be sure that the drivers have the potential to sound better than the speakers I already use etc.

An obvious contender for the bass drivers would have been the SB Acoustics MW16/MW19 “Satori” drivers, but a couple of weeks ago I spotted a unused (but not new) pair of 7″ Scan Speak Illuminator drivers which pretty much met all my criteria as well. “Cheap” is obviously a relative term but as I could get the Scanspeaks for around the same price as the Satoris cost new I decided to grab the Scanspeaks instead and a few days ago they showed up.

Next up is finding some suitable tweeters. The matching Illuminators are the obvious candidates, but rather than paying list price for those I’ll wait a little bit and see if anything interesting comes up on the second-hand market 🙂

More finished stuff!

Although there is a tiny bit of light at the end of the Covid-19 lockdown-tunnel (at least in my part of the world), the “new normal” (or at least “interim-normal”) of working from home and attending lots of online meetings still continues. This means I also continue to have more time than usual for building, so I’ve managed to complete a few more projects over the last week or so. I know it might not seem that much, but compared to my usual rate of progress it’s starting to feel like an assembly line! 🙂

First up is the AD1865-based DAC I showed here. It works as intended and sounds fine, but honestly I need to redo the wiring because it’s not really optimal. Not now though 🙂

Next is my 50ASXBTL-based amp. This is the original “prototype” I did of the SE-BTL conversion for the ICEpower 50ASX modules and while there have been some reports on diyaudio that the conversion isn’t as straightforward as I made it seem, I can confirm that at least based on sound the finished product still works well.
However, the last strech of this build wasn’t without issues, firstly because I had to redo the bottom plate as I realised that glass fuses on the primary side of an SMPS is not only a bit stupid, but also not necessary when each PSU is already fused on the board. Secondly, that turned out to be the easy part because I did most of the wiring by memory which in hindsight wasn’t the best choice. Anyway, after a few more attempts than I expected (and after swearing at everyone and everything including my own stupidity) it actually works well now – nice!

Last, but definitely not least, is the basic ICEpower700AS2-based power amp I showed here. This deserves a new 10mm custom front panel at some point, but it plays well and for now I think getting some more listening impressions is higher on the agenda. My initial impression is that this could well be my all-time favourite ICEpower-amp, but let’s see how it goes when I put a few more hours on it.

Hopefully this week will bring a new batch of front panels (or actually, rear panels) so I expect to be able to keep up the current level of progress a little while longer 🙂

Easter blues…?

Easter breaks are particularly long in Denmark and this year I’ve extended mine even further. Even though the changes this year are smaller than usual due to the corona-virus quarantine, not having to attend (online) meetings during the day does make a difference. Being stuck at home for a few weeks have also given me plenty opportunity to look at my pile of semi-finished projects and thinking I should get some of those finished 🙂

The main purpose of this year’s break was to do some non-audio related DIY around the house, but I still found time for some audio-stuff as well. Mostly I’ve turned projects from partially completed to a little bit more (but still partially) completed which doesn’t make for interesting pictures, but this progress has also meant being the able to order some missing parts (mostly panels and PCBs) and experimenting a little with some new designs as well. Hopefully, with a few more long weekends in sight, I should be able to complete some more stuff over the coming weeks.

A couple of things did make it to “fully completed” though: One is a balanced monitor controller based on the THAT1646 (first mentioned here) and the other is my pair of TK2050-based Helder Audio monoblocks that I started here. Not much to either of these to be honest, except that the last bit of wiring is usually what I end up spending the most time on. Both of these work well, but I don’t really have any imminent use for them. The TK2050 is still a good amplifier (as I remembered it to be), but it is now an older design and admittedly the world has moved on in comparison. Still nice to finally get to “close the lid” on a build from time-to-time though – it is a good feeling! 🙂

Project files: The NE class A headphone amp…

I’ve now finished my testing on the NE class A headamp I described earlier, so here are the design files if anyone else thinks it looks like an interesting design and wants to give it a go 🙂

XP-7 headamp clone…

Another build I’ve managed to finish during the past week is the XP7 clone (originally shown here). As I explaned originally this is more or less a standard OPA+BUF634 amplifier with the only real “USPs” of this implementation being the use of AD797 opamps and lower gain resistor values than usual – both of which should help reduce noise.

I’ve done my bit for noise reduction as well by making the amp powered by two 9V batteries – I haven’t tested the battery life yet, but hopefully it isn’t too bad 🙂

Regardless of that I don’t particularly need another headphone amp as I don’t really listen to headphones that often any more. However since this one is battery powered I will not pack it too far away, because a battery powered amp is quite useful for testing (due to no ground loops). And, after a little bit of listening to the finished product I have to say that it doesn’t actually sound bad at all…

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 😀

A tweeter amp…

Another overdue board design that finally showed up recently is this one. I would not call this design one of my “heroes” (like the last post), but it’s probably one of the “most-revised” since this version is actually the third iteration (although I honestly haven’t ordered or built the previous two iterations – not entirely sure why…).

So why is it called a tweeter amp? Well, two reasons: One is that the original intention was to supplement a single-supply class D amp in a bi-amp (plate-amp) setup, especially the power take-off on an ICEpower 200ASC/300AS1-module. The other reason is that if you want to improve the sound quality within the limits of the small board you’ll get a low-end roll off that means the amp is not going to play a lot of bass at all, but for a dedicated tweeter amp it is still perfectly usable.

The circuit is simple – it’s basically my version of the bog-standard single-supply circuit of the LM3886 IC (or its cousins, the LM3876/LM2876). With the kind of power supply you normally have available (single 45-55VDC) you only get 20-30W output, but as a dedicated tweeter amp this goes a surprisingly long way (and even further if you use an active filter in front of it). I have to admit that this idea is not actually mine, but something I have seen a manufacturer of active PA-speakers do several years ago (exactly with the ICEpower200ASC module as the bass amp and PSU).

The board works as-is, but it’s got a bigger turn-on thump than I would like so I need to see if I can get that a bit lower somehow. Otherwise I seems workable as-is – and my first impressions of the sound quality are actually also very good. I don’t have any of the ICEpower-modules at the moment, but I’ve got some industrial switching PSUs that I want to try out as well to see if they work.