New toys…

As per my last post I am in the process of moving (a lot of) DIY stuff out of my apartment, so what I should definitely not do is buy more things. However, sometimes an offer comes up that you just have to jump on 🙂

This time it was a set of unused ICEpower 700ASC-modules which is one of the ICEpower models I have not yet tried. They came up on a local classified page last week where I just spotted them by accident. The price was reasonable and since this is the ASC-version of the 700 with a few extra useful features then they should be quite versatile in use.

For now though, they are going on the shelf while I look for a suitable project for them (and move them to the new house 😀 ).

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A brief intermission…

Over the next weeks until Christmas things are likely to be even more quiet here than usual as I will be moving from my current apartment to a (small) house 😀

It’s only a few miles away but since I have to juggle all the moving tasks together with my normal job it’s going to take some time and focus away from other tasks. Also, given the sheer amount of audio/electronics stuff and (mostly) half-completed DIY projects that I have to pack up and move as part of the process then it is going to be a bit of a challenge. On the plus side once I’m settled in I should have a bit more space for my parts and projects 🙂

There might well be updates in the mean time as I have several projects in the works that are nearly ready to write about, but I can’t really guarantee anything at the moment. Since winter is getting closer it also means just taking pictures in daylight is more or less reserved for the weekends 🙂

Last, but certainly not least, I’ll finish 2017 and start 2018 with a two-week trip to Asia which normally ends up being a little audio- and DIY-related so maybe there will be some updates from that as well.

In any case, “normal” service – whatever that means – should then resume some time in January 😀

Project files: PassHP headphone amp

What is it?
It’s the project files for the PassHP headphone amplifier from last week’s post and judging by the number of views since then they are eagerly awaited 😀
As mentioned last time, this design is a clone of the one from here and my version consists of a mono amplifier board and a stereo PSU board instead of the original “all-in-one” design.

How big are the boards?
The amplifier boards measure 2.95” x 3.0” (app. 75 x 76 mm.) and the PSU board measures 2.0” x 5.05” (app. 51 x 128 mm.).

What is the status of the boards?
Both boards are in version 1.0 as the prototype seems to work well and I couldn’t be bothered to make any cosmetic changes 😉

Does it use any special/expensive/hard-to-find parts?
Well, the recommended 2SJ313/2SK2013 output transistors are a bit hard to find, but there are plenty of substitutes available. This is a fairly simple design, so otherwise no problems.

Anything else I need to know?

  • Resistors: I’ve used RN60-type resistors which are rated 0.5W, but that probably isn’t necessary – at least not for all the positions.
  • Heatsinks: The heat sink profile is the one Fischer calls SK104 but there are many substitutes. The power dissipation isn’t great so even the small 25mm high version should suffice, but if you want to use bigger ones for cosmetic reasons that should be just fine 🙂
  • Transistors: I’ve used 2SJ313/2SK2013 output devices because I had them, but if you don’t then I recommend using IRF610/9610 or one of the other substitutes mentioned in the diyaudio build thread. The 2SJ/2SK pairs are now either very expensive or very fake (and sometimes even both!), so using parts that are still in production should be safer.
  • Optocoupler: In theory this is also substitutable for something else, but in all honesty I don’t know exactly how the optical bias-system works so it’s probably best to stick with the standard 4N35.
  • Gain: The default gain is app. 6 but that can be lowered or raised by tweaking the value of R4. In theory you should recalculate the BW-limiting capacitor across the resistor if you change the value, but in practice you’ll probably be fine unless you make major changes. My prototype version has a gain of 3 (R4 = 2k) and I haven’t observed any problems.
  • Opamp: My version uses a single-channel opamp which gives a bit more choice. Start out with something like the OPA604, OPA134 or LME49710 and then experiment from there if you want to change the sound.
    Most opamps have a max. supply voltage of +/-15V so as a starting point I’d recommend this as the supply voltage. If you want more voltage swing use the OPA604 which is good up to +/-22V.
  • PSU voltage adjustment: Just as in the original you can use LEDs to raise the output voltage of the supply above the regulator voltage (although I’ve ditched the resistor option). Using 7×15-regulators and green/red LEDs should give you around 17V output whereas using 7×18-regulators and LEDs should bump that to app. 20V. If you just want the regulator voltage as the output, remember to jumper across the LED pins and omit the capacitor.

Downloads:
Download design files here

Related information:
You really should chew your way through the diyaudio-thread for information about the amplifier. As mentioned this version was mostly because I did not like the original form factor. If you just want a functioning amplifier then I strongly recommend that you buy one of the “real” boards from Wayne Colburn via DIYaudio (or wait a few weeks for when the boards show up in the diyaudio store).

Note: Always read the “intro post” for additional important information about my designs.

New PassDIY headphone amp…

One of the (few) PCB-projects that I have been able to spend time lately on is a version of a new PassDIY headphone amp developed by Wayne Colburn. I’ve been looking at this from when it was first posted (after all, most diy’ers watch with interest when Nelson and his gang are up to something new 🙂 ) When the design was finally released a few months ago and Wayne started offering boards I didn’t jump on it immediately though.

First off all there was a question of cost – paying $35 in shipping for $25 worth of PCB is a bit annoying although I probably would have survived that. Secondly, the “all-in-one” form factor has some very obvious benefits, but also some significant drawbacks to me. You’re generally tied to one particular chassis, one particular transformer, one specific potentiometer etc. and I wanted more flexibility.

So instead of getting a ready-made board I started thinking about making a more flexible version by splitting the board up into smaller sections – two mono amplifier channels and a separate supply board to which you need to add a separate volume control and a separate transformer. The design is simple and so there were no major issues and my protoype fortunately worked the first time.

As usual I have only done quick bench testing right now, but the design seems to be solid (no doubt more to the designer’s credit than mine 😀 ). There is no DC-offset worth mentioning although it spikes a little when you turn the power off, and even in a “birds nest” test setup with wires all over the place, the amp was completely silent. As far as I can see, the bias is spot on and stable as well.

Project files coming in a few weeks when I’ve had time to compile them 🙂 In the mean time, you can still get the original boards through the thread and the original Gerbers are there as well if you want to get your own boards made instead.

Small thing – big difference

I don’t normally write (much) about the commercial gear that I buy, but for once I’ll make an exception.

I’ve actually owned both the previous versions of the Audioquest Dragonfly (DF) USB DACs but sold them after a relatively short time because I did not really need them anyway. Thanks to an ad on a local classifieds page I now find myself as the owner of the third generation DF as well – the Dragonfly Red. Apart from the new looks – which I really like – the new series of DFs also have the benefit of much lower power consumption, meaning they can be used with mobile devices.

I therefore tried hooking up the DF to both my iPhone and iPad. To be honest I wasn’t expecting that much, but it really does make a significant difference to the sound quality. The downside is of course that your phone becomes quite a bit less portable with a couple of extra dongles and adapters hanging off it, but the benefit in sound quality seems worth it. I wouldn’t use it every day, but if I really had to travel light then using the DF would save me packing and carrying a separate music player which could be very handy.

Photo of the device and a “real” red Dragonfly as well for comparison 😉 (that picture was taken by yours truly in Hong Kong – coincidentally exactly two years ago today)

An ICEpower 50ASX amp – the easy way…

Some weeks ago a reader on the blog asked me some questions about various pre-made options for putting together a simple amplifier based on the ICEpower 50ASX2 module.

One of the options mentioned was to buy a case-kit for the module from Ghent Audio in China. I’ve seen pictures of these cases before and not only do they look quite good, they also come pre-drilled and silkscreened which for most DIY’ers is the hardest part of building stuff. I answered the questions as best I could without any hands-on experience to offer, but as I had an older black 50ASX-module left over I decided afterwards to get a case for myself and try them out.

After the usual waiting on shipping (which wasn’t actually that bad – app. 2.5 weeks), the case kit arrived. Everything is included, a power switch assembly, AC inlet, terminals etc and it seems to be decent quality all round. I didn’t buy the full cable kit, which would have made it even easier to assemble, but still it’s not too bad.

Putting together the basic kit with the module, feet, switch etc. ready for cabling only took around half an hour or so. If you look at the pictures I’ve made a few “adjustments” to the kit by using stainless screws and feet (the kit comes with black screws and matte silver feet), but otherwise it is as delivered and of course using the original parts would also have been just fine. The terminals are decent quality, but not the best I’ve seen. Also, the terminal holes are drilled too large (presumably to accommodate changing suppliers) which is slightly annoying but by no means a deal-breaker.

A bit more digging in the parts drawers revealed some suitable pre-made cables for signal and speakers – and a problem: my stock of JST connectors for the power connections has run out (or run away :-))

So yes, in conclusion this is definitely an easy way to build an amplifier (just as long as you ensure you get all the parts before you start 😉

Distractions….

Once again I find myself in a period where “real life” is intruding significantly on my build time. Not only at work (which is the normal reason), but also in my personal life. Therefore, the progress I am managing on my projects is mostly so incremental that it doesn’t really make sense to write about it – it would be the DIY-equivalent of a book with every page as a separate chapter!

However, the inspiration for projects is still there and both the various online forums and my blog-feed serve as good sources of new ideas and inspiration. One recent example that I specifically think is worth mentioning is this post on Arduino “watchdog timers” for standalone Arduino projects where a self-reset capability in the event of an error is a good idea. Like all the other posts on the site, this is very comprehensively documented and easy to follow and in this case it’s a topic that I didn’t think about but immediately thought would be useful.

And the best part is that even if you are busy, sketching out a simple PCB doesn’t take that long – does it? 😀

(note: hat-tip to the referenced wikipedia-article for the image below)

Hypex UcD in progress…

It’s been quite some time since I have posted about a project that I have actually completed – and so I’m a little ashamed to say that this post won’t break that trend 🙂

It’s a class D power amplifier based on Hypex UcD400HG modules. As with many of my other projects, it started with a few leftover parts and some thoughts about what to make from them. In this case, it was the chassis and the “centrepiece” of the design, namely a gigantic 1000VA transformer. Trying to decide what to do with that lot soon led to some obvious choices:

  • It had to be class D because there was very little space for the actual amplifier and heat sinks once the transformer was installed 🙂
  • The “upstairs/downstairs” layout that I have mentioned before became a necessity to make use of the internal height of the chassis.
  • I wanted to reuse my PSU-boards because I already had spare PCBs, but they wouldn’t fit and so I had so make a smaller version.

I know Hypex has shifted to their newer N-Core technology and started building integrated modules with onboard SMPS, but the old UcD-modules still have a reputation as excellent amplifiers. The plan is to upgrade them with the Hypex HxR-regulators once I confirm that everything is working properly.

The “final problem” is how to provide heat sinking. I have my eyes on some pre-made heat sinks that should do the job, but they are from a supplier where I don’t normally order so costs are a bit higher than I would like. I might eventually break down just to get it over with, but in the mean time I have a couple of other options in mind as well 🙂

PeeCeeBees in a box…

Well, almost. At least the box is ready for the PeeCeeBees, even if they are not quite ready for it yet 😀

Apologies for the stupid puns, but I managed to (nearly) finish the chassis for the PeeCeeBee amplifier boards. The basis is a small ebay-sourced enclosure with side heatsinks, but I have replaced the rear panel and fitted the insides with custom mounting panels for the PSU and the transformer/softstart.

The “upstairs/downstairs” layout maximises internal space and is something I plan to reuse extensively on other projects (even if the cost of the custom panels from Schaeffer/FPX does begin to add up…)

Still to do is some transistor matching (bleh!) before I can finish and test the boards and I also need to order a new transformer – the one in the picture is the right size, but not quite the right voltage.

First Watt F4 (part 1)

I don’t normally build class A amps in the summer because my apartment gets really warm, but this time is an exception. Partly because this summer in Copenhagen has been much more “class A amp friendly” (i.e. a lot colder!) than usual, and partly because this is a design I’ve been wanting to try for a very long time now.

The First Watt F4 is a classic Nelson Pass/First Watt design with JFET inputs and MOS-FET outputs. However, as with the other FW amps there is a twist here, namely that the F4 has no voltage gain. That means it’s essentially a buffer than can provide a full 25W class A output. What’s the point of that you might ask? Well, one point is that it can help get a better gain structure and that it’s possible to use some sources (such as DACs) which have a very high output. There are various other applications in the F4 manual as well.

Some will have spotted that the F4 boards are from the diyaudio store. They are good quality and a well-proven design, so I decided not to bother doing my own.

The chassis is sort of the usual from Modushop, but then not quite anyway. Partly because the heatsinks are predrilled 4U types from diyaudio (which did cost a bit more, but saved me drilling and tapping nearly 30 M3 holes) – because they match the boards 100%, and partly because I have decided to do a bit of “hacking” to make a non-standard size chassis (teaser! 🙂 )

So, in addition to the chassis hacking, I am also thinking about which preamp to choose to provide the voltage gain for this and obviously there are plenty to choose from, so it should be possible to come up with an intriguing combination for you guys 😀

Soundwise I also have quite high expectations because of my past experience with the First Watt F5 design – which I still consider one of the best sounding amplifiers I have tried in my home system – but let’s see if the F4 delivers on that front as well when it’s ready 🙂