Holiday plans…

For the last week I’ve been having time off for my summer holiday – and I have another week left to go. This year I decided not to (really) travel anywhere apart from a couple of short trips in Denmark, but instead stay at home and tackle some DIY projects. Its mostly outdoor projects around the house and garden – some of them waaay overdue! – but there’s also some time for audio as well.

Much of the progress on my projects is very incremental, i.e. moving several projects forward but not finishing anything, but that is sometimes still quite important for me. Also, with more time for concentrated working (and thinking) than I can normally squeeze into a working day, I have managed to crack some “hard problems” in the form of unfinished design sketches and stalled PCB layouts. Just like in my day-job, being able to concentrate my focus on these challenges does wonders even though it doesn’t necessarily mean concentrating my time on them (= I’m not sitting staring at the Eagle screen non-stop 🙂 ), and so I’ve managed to send a good amount of PCBs off to manufacturing last week as well.

As I have started ordering PCBs again, I’ve also been spending time trawling DIYaudio.com for interesting amplifier designs and free Gerber files. Managed to find a few that look good (mostly by diyaudio-member Prasi and in this thread), so I put those in the PCB orders as well. Completely irrational considering I am trying to move to active loudspeakers and I already have a ton of unfinished projects, but when the initial marginal cost is only a few dollars extra for the PCBs it’s very hard to resist… 😀

One of the things I have been spending most time on lately is my loudspeaker experiments and that brought up the realisation that a more dedicated “testing platform” for loudspeakers might be a good idea in the longer run. So far I’ve gotten by, either by using the Hypex DSP prototyping-amp or by simply filling the living room with random amplifiers and cables.

Neither solution is really long-term viable though, so I set about designing a dedicated prototyping-amp that would allow me to connect a suitable front-end (= a basic DBX active filter for now…) with a single-box amplifier that can run a pair of fully-active 3-way loudspeakers.

The idea has been germinating for a little over a month so I have already made some progress I can hopefully show later (along with some pictures), but I hope I managed to put my ICEmatch-amplifiers to some good use 🙂 There are still some details to work out regarding cabelling, but hopefully nothing I can’t crack within a reasonable timeframe 🙂

Distant cousins?

I’ve showed off my fascination with (small) coaxial loudspeaker drivers before and recently I scratched the itch again with a pair of SB12PACR25-4-COAX.

This is a new driver from the “cheap” SB PFC/PAC lines. Like the Seas driver it has an alu cone and a softdome tweeter, but the price is around 1/3 of the Seas driver, courtesy of cheaper SB manufacturing and a cheaper plastic basket compared to the die-cast aluminium on the Seas. That said, it doesn’t feel that cheap to be honest, because even though the basket is plastic it seems well-made and solid. I have several others of these PFC/PAC SB drivers and they as well-engineered as the rest of the SB lineup IMO and excellent value for money. In case you doubt their “audiophile credentials”, there is even a Troels Gravesen design based solely on the PFC-drivers.

Now I could have just bought the paper-coned version of the coax-driver that has been on the market for years, but I have the 16cm version of that already, the price was about the same and I thought it would be fun to compare the alu-version to the Seas L12 – oh, and I think the alu-version looks cooler as well :).

This is one of the drivers that I have bought with a specific project in mind, namely to try and build a small active all-in-one “desktop” speaker. The original plan for that was a three-way design with a small built-in subwoofer, but the enclosure ended up being very large and impractical (i.e. desk-sized instead of for desk use…). Two of these SB12s plus some electronics is an altogether more reasonable size, so I have repurposed the other drivers for something else instead.

I’ve already cut some wood for the basic design and with a holiday coming up soon, I hope in a week or so I can get these drivers into cabinets and do some basic listening tests. In parallel I am also looking for suitable electronics, but that’s a story for another time (mostly because it’s not done yet 😉 )

Collateral damage…

The weather isn’t really supportive of indoor activities at the moment, so not much building going on. When the sun shines in Denmark you have to make the most of it, so I try to prioritise outdoor activities instead :). However, it’s always good to make plans for what to do indoors when the weather changes…

As mentioned in the previous post I have been online-shopping for interesting power amp designs lately. I managed to find a few, but as usual when I look for PCBs I don’t just find what I need but also – inevitably – a few things I didn’t know I needed 😉

One of those finds this time was a Pass (-inspired) preamp board. It’s a complementary design with IRF610/IRF9610s and switchable gain fed from a single 60V power supply rail. I’m not sure if this is really a genuine Pass-circuit (at least it’s not one I immediately recognize). However, it looked interesting and I had most of the key parts available already so I decided to take the plunge anyway.

A few bits and pieces missing still, but it shouldn’t be long before I know if the board was worth the investment…

Meeting Kumisa (again)…

My transistor-haul from a few weeks ago let to a bit of time being spent on ebay and Aliexpress looking for interesting power amp designs to try out. Some of those should start to trickle in over the next weeks, but what I also found was a headamp clone that I almost bought – the CK2.

The CK2 is derived from an ancient design called the Kumisa III published on Headwize. It was updated by Ti Kan of AMB and a few others in a head-fi group design around fifteen years ago(!). It was one of those designs I looked at and never really tried, but after being reminded that it is still out there I dug out the pair of PCBs I bought many years ago. Rather than buying a clone board (which does look good BTW) I decided to start on the original instead.

One of the things that kept me from building the original CK2 was simply that it uses 300mil resistor holes to save space. Bending the RN55 resistors I used for everything at the time to fit the 300mil holes is possible, but it’s a bit annoying and fiddly to do. However, nowadays that problem has solved itself because the RN55s cost me around one euro each (!) in small quantities so I’ll save those for something else. Instead I bought some smaller resistors in the right values and they are much easier to work with. I needed the same type of resistors for something else as well, so although the values were different I had already found the right type at Mouser.

The board is pretty easy to work with and although I am short some key parts (and some transistor matching) right now, it should not be long before I get that done and then I can check this design off the list as well – a few years later than expected! 😀

No more class D?

I do most of my electronics-related shopping on international websites, but it still pays to keep an eye on the local classifieds. The audio market in Denmark is small (even though we have a reputation as a big audio nation…), which means that some things are very expensive but also that the occasional deal comes up 🙂

Last week I managed to pick up a batch of NOS Toshiba 2SA1943/2SC5200 power transistors. There are just under 100 pcs of each type and the seller has already done some basic hfe-matching – nice!
They were bought from someone within the industry and I am assured they come from a reputable source (digi-key) so although I couldn’t pick them up in person I felt it was a chance worth taking.

Having now looked at various pictures online they look as genuine as I have ever seen them, so that is obviously great. Do I need 100 pieces of these for my projects? No I don’t, but the price was much too good to pass up so there was no reason to split up the batch 😀

As most will know these transistors are a staple of class A and AB amplifiers where they are used as output devices. And no, that doesn’t mean that I will stop buying/building class D amps as the title alludes to. Class D still has a place and many advantages over conventional linear amplifiers in my view. It does mean lowering the barriers for building some class A and AB amps though, so think of it as an excuse to do a bit more experimentation here in the future 😉

More bass…

Not a whole lot of “broadcast-able” updates at the moment, but a few things are moving in the background. The last speaker project to be finished (at least for now) is more or less done though – a small subwoofer.

I had this as a “real” subwoofer years ago when I had a surround-system, but I didn’t really need it and so to save some space I eventually threw away the old cabinet and kept the driver – a Vifa MA26. The driver is actually quite nice with an alu cone, carbon fiber dustcap and optimised for closed boxes so just what I want in a sub. That said, it doesn’t really have a lot of monetary value so rather than try to sell it I decided to build another version of the box instead.

The old sub had a DIY plateamplifier without a built-in crossover, but I wanted a real to make the new sub fully stand-alone. After looking around for a second-hand Hypex DS or similar for a while (and not finding anything), I stumbled upon a DSP-enabled Dayton Audio SPA250DSP that was sold off cheaply by a German dealer. It was a little bit more expensive than I originally wanted to spend, but the DSP-features actually make a lot of sense for this project so I took the plunge anyway.

The box is nothing to write home about, but it’s going to be hidden away so I’ll use the “prototype” excuse and leave it at that ;). Now I don’t really need a subwoofer for my office, but even so this is going under my desk (once I clean up there…) for a bit of added “oomph” to my music when I am working at the computer 🙂

The built-in filter of the plateamp also means that I might look into new desktop-speakers to replace the Adam Audio monitors I currently use, but that’s definitely a project for another time 🙂

Here we go again…

Yes, it’s another anniversary – number nine this time.

Don’t think I can say much that I haven’t already said in the previous anniversary posts, but I am still here. I also fully plan to post something more profound this time next year, so I better start thinking about it right away…. 😀

This post is number 345, so let’s see what we can manage to hit next year 🙂 Thanks again for reading, commenting and asking questions – that is still what makes it worthwhile to continue 🙂

Testing the waters…

Continuing the loudspeaker-streak here, this time with some actual (test) speakers. A pair of cheap and interesting SB16 coaxials bought for a potential project, but – at least for now – repurposed as a simple 2-way testing platform. These will allow me to get a little acquainted with Hypex Filter Designer (HFD) and active crossovers using my Hypex FA123 “prototyping amps”.

I was honestly dreading this a bit because I have the impression that HFD is quite complicated and at least it looks a bit daunting at first glance. It probably is complicated, but with a printed copy of the manual next to me it was the work of barely five minutes to set up a basic LR2 filter at 2.5 kHz, upload it to the amps and get sound out. What’s more, it was actually pretty good sound despite the fact that I didn’t do any measurements beforehand and just picked a more or less arbitrary crossover point. That seems encouraging for further experimentation at least.

As a prototyping platform it seems like these SB Coaxials are really good, but then I was expecting them to be at least “OK” since the basic design is based off one from German designer Udo Wohlgemut. I’ve also been reminded lately of how much I like Neutrik Speakon-connectors, it really is a good system that doesn’t get anywhere near the credit it deserves for home use.

Cabinet-wise these boxes are closed like the bass-modules. I wouldn’t say these are deliberately ugly, but I certainly didn’t spend time making them look good though ;). The closed boxes also mean they don’t really play low bass, but since the integration to the bass modules is one of the things that I need to experiment with that’s probably a good thing anyway.

A few more hours of playing around with filters and measurements for these, and I should be ready to start working with some “real” drivers – more cabinets are already in progress!

A solid base…

Yes, more speaker progress…

This week I’ve finished a couple of different bass modules. As title sort of alludes to, the purpose of these boxes is not just to cover the lower frequency area but also to serve as stands for a pair of smaller speakers (of which I have many planned 😀 ). I am used to floorstanders by now, but the “2+1” way configuration is something I want to experiment with as it seems to be a good and quite flexible configuration.

The smaller boxes are a pair of CSS SDX10 drivers in closed boxes. The SDX’s I picked up around a year ago on my local classifieds site. They were slightly used, but they look to be in perfect condition and the price was too good to pass up.

The larger boxes are Scan-Speak Discovery 26W-drivers (26W8534G). These area alu-cone (which i consider almost an ideal material for low-frequency use) and they are also closed-box, because it should give a better quality bass and – more importantly – a better coupling to a smallish room. Like the SDX’es I also bought them second-hand for experiments, but to be honest the price here was better than good 😀

I forgot to take a picture of the back of the 26Ws, but after moving the empty cabinets around for a while I decided to put a grab handle on the back of each box. When there is no reflex port, getting a good handle on them when they have to be moved was a bit difficult. Seems to work well, as long as the handles are solid enough to take the weight and bolted onto the cabinet (not just screwed into brittle MDF).

The finish is raw MDF for now, and while the enclosures are OK, they aren’t what I would call furniture quality. However, I am quickly running out of space for all of these speakers, so I need to do some comparisons and then decide which ones should stay anyway. The SDX enclosures are a bit too small to use as stands, so if they end up staying I probably have to redo them at some point, but after having done a few projects I think it will be both much faster and less daunting than it has been before.

On to some “real” (prototype) speakers next! 😀

Promising sounds…

It’s been the Easter break here, which I once again took full advantage of. “Full advantage” in Denmark means 10 days off work and just because I felt like I needed a break, but also because I’ll be starting a new job in the beginning of May so it felt like a good time to relax a little.

After a (predictably) slow start, I did actually manage to do quite a lot of stuff during my days off. Since the weather was nice most of the time it was time to start working outside and that meant working on some loudspeaker projects. To cut a long story short I managed to finish a few things, most notably the full range Seas FA22s that have been waiting for better weather for a few months.

I’ve stuck with the standard Seas design of a 60L closed box for the FA22, but instead of the short and deep enclosure design proposed for the FA22 I have gone with the more traditional floorstanding form factor suggested for the more expensive Seas X1 full range (with a simplified internal bracing setup).

As the title alludes to I’ve only just managed to connect them up and listen to them, but I have to say I am impressed already. As there is no filter to correct the frequency response some kinds of music including most male vocals sounds a bit anemic, but I think the filter might help with that. On the other hand the soundstage is very good, the resolution and timbre on most female vocals is excellent and there is obviously some bass as well.

First order of business now is to play a little with the recommended filter values and also some additional EQ just to see how much sound quality it’s possible to extract from these drivers. If they live up to the initial promises I’ll have to do something finish-wise to the cabinets, but for now I can live with the raw MDF 🙂