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 😉


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 🙂

Project files: A smaller mains controller…

What is it?
As mentioned a few weeks ago I’ve recently built another control board for switching a mains transformer with a low-voltage (latching) switch. This in a slightly different form factor so that if your application requires it, the board can be stacked with a matching standby-PSU and mains splitter and/or my passive softstart board. It is possible (just) to stack all three boards on top of each other in a 2U/80mm high enclosure or just two boards in a 50mm tall enclosure.

You can decide which standby voltage should be used by choosing the right relay in resistor values and in addition to using a latching switch for engaging the relay, you can also use a DC-voltage between app. 3-30V as the trigger. This input is isolated via an optocoupler and the trigger circuit only requires app. 15mA from the triggering device.

The matching standby PSU board uses the (by now) well-known IRM AC-DC power modules from Mean Well. There are two versions, one for the 3W module which is 100% outline-compatible with the control board and a version for the 5-10W modules where some of the connectors had to be shifted but the mounting holes still fit. The PSU board also provides a splitter-function to give two mains outputs.

How big are the boards?
All the boards are 2” x 2” (app. 51 x 51 mm) – the original theslowdiyer industry standard ™ 😀

What is the status of the boards?
These boards are v1.0 and they all work as expected.

Does it use any special/expensive/hard-to-find parts?

Anything else I need to know?

  • The switch must be a latching type (meaning it stays in either on or off positions) and to turn the relay on you connect the switch so that the + voltage is connected to the switch pin. This turns on a transistor which switches the relay on.
  • The relay is rated for 5A inductive loads, so should be good for transformers up to around 1000VA at 230VAC (to give a bit of safety margin).
  • The optocoupler on the trigger input is fed from a constant-current source (CCS) made from an LM317L voltage regulator. If I was designing a commercial product this would probably be a sacking offence because it’s much more expensive than the alternatives, but for our purposes it works quite well 🙂
  • There are two LEDs on the control board, one to indicate the board is powered and one to indicate the relay is on.
  • The “ext” output is intended for us if you want to feed the unswitched standby voltage to some other circuit. There’s space for a bigger resistor here if you need to drop voltage for e.g. LEDs, but you can also jumper the resistor to just get the raw voltage (or leave the output if you don’t need it).
  • The mains connectors on the standby-PSU are marked as inputs and outputs, but in reality it doesn’t matter what you use as inputs and outputs.

Download design files here

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

Remember that these boards use mains voltage. Be careful when mounting and handling them!

PeeCeeBees in the wild…

First of all, let me apologise for showing yet another half-finished board, but there’s a reason for that which I will get to later. Secondly, apologies as well for the stupid headline, but unfortunately this is the name of the design so I did not choose it 😀

The PeeCeeBee amplifier is as far as I can recall a version of the VSSA (Very Simple Symmetrical Amplifier) developed by diyaudio-user LazyCat and a precursor to his “FirstOne” semi-commercial design. The VSSA is (as the name sorta implies) a simple amplifier based on Lateral MOS-FETs which are excellent for audio and the PeeCeeBee circuit has built on the concept.

The PeeCeeBee design has gone through several iterations, but this week I received my boards from the diyaudio groupbuy of the v4 design from Shaan in India. The group buy boards are black (which would not have been my first choice because you can’t see the traces very well), but they are 2.4 mm thick(!) and excellent quality so I couldn’t really wait to start putting them together.

Now the reason for posting this now is that there is a second run group buy which runs until the end of the coming week, so if you missed the first round there is still a little time to secure your own boards 😀

Still short a few passive parts for the boards, but I have the LAT-FETs on hand, I have a suitable chassis on hand and probably a transformer as well. I’ve never built a LAT-FET amp before, so really looking forward to hearing this one “in action” in (hopefully) a few weeks when the last parts get here.

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 🙂