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 😉


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 🙂

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.


One of my (numerous) neglected projects is a version of the “HackerNAP” Naim clone amplifier. Naim is one of those brands that have a very loyal following, and many of their original designs have been analysed extensively by DIY’ers looking for improvements. The HackerNAP is one of those derivatives and the NCC200 from Avondale Audio is another – ebay is awash with other (more or less accurate) versions as well by the way.

Part of the reason why this project hasn’t been top of the list is that did not like the original HackerCAP PSU boards, so with a small delay (of around three years…) I decided to do my own version instead 😀

To be honest this isn’t how I would normally have done a PSU board – if had designed from scratch I would have made a larger board, used two full bridges and a full ground plane – but as the chassis are already drilled for the original boards I kept the physical size as close to the original as I could.

While the board size isn’t 100% the same as the original HackerCAP, I’ve retained the option to configure the design for both “normal” PSU usage and also for CRCRC or CLCLC configurations.

As the PSU boards are now done and tested, I can hopefully manage to do the rest of the assembly in less than three years 😀

Sunday morning chipamps…

It’s been some time since I did an ebay kit, but that doesn’t mean I have given up on them (in fact I bought plenty…) and a cheap kit is still a great thing to play with on a Sunday morning**

It’s a pair of power amps based on paralleled TDA7293 amplifier ICs in the correct “master/slave” configuration as per the data sheet (and this discussion on diyaudio). The TDA7293 and TDA7294 chips are among the few survivors of the “purge” of audiophile components and they should still be available. Unlike the LM38xx-series and its siblings, the TDAs have MOS-FET output stages which means they can run in parallel without resistors to limit current sharing between outputs. The parallel arrangement allows for more current into low-impedance loads, but as the TDA7293 will work on up to +/-50V rails having two ICs also makes for a fairly serious effective power output.

These kits are seriously cheap and although I’ve tried to use most of the components that came with the kit, some parts have been replaced for cosmetic reasons (because that matters to me, sorry!). Even with component replacements though, these kits are so cheap that there is no real excuse for not trying them – even if you don’t need new amplifiers at all 😉

No real sound impressions yet, but I know these chips can sound really good so I am looking forward to seeing how much of their potential can be unlocked for the same price as a takeaway meal 😉

**Yes I know it’s not Sunday today, but as Whit Monday is a holiday in Denmark it felt like Sunday morning 😀

Class D experiments…

There are many class D technologies on the market at the moment, but one of the ones I haven’t tried (until now at least) is the International Rectifier “IRAUD7”-amps (IRF has been acquired by Infinion).

Consisting of the IRS2092 driver IC and various purpose-built FETs (many of them two FETs in a single package suitable for half-bridge designs), this is by most accounts a good-sounding and scalable class D technology. It’s also one of the few technologies where you can actually have a go at your own PCB layout if you want to. The schematics are available in IRFs published reference designs (here and here) and although making good PCB layouts for high-power switching electronics isn’t easy, it is actually possible to do.

Of course, when something is so easily available it tends to get exploited. It wasn’t long after IR introduced the designs before the market was flooded with several cheap clones, some using their own PCB layouts and some using IRs own Gerber files which are also published on the website. I had my eyes on some small (credit-card sized) boards to try for a while as they were really cheap (do an ebay-search for “IRS2092” and you’ll see 🙂 ), but eventually spotted this “luxury” version (at least based on appearance and observed parts quality) and fell in.

This build is the “low power” version with the IRFI4019 FET, but there’s also higher-power version with the IRFI4020 FET. Since the seller I bought from made a mix-up in ordering I actually ended up having a pair of each version, but I wanted to start with the low-power version. Then I might go dual-mono on the high-power boards later on if the sound quality proves it worthwhile 😀

The PSU consists of a 200VA transformer and a cheap supply PCB with 45mF capacitance per rail – mostly because that was what I had in my parts drawers. I’ve tried to keep the mechanics as simple as possible since I consider this build an experiment, but having the amp and PSU on a mounting plate simply makes everything much easier so I decided to “splurge” a little anyway :). The front panel is blank until I decide how the amp is going to be used.

Even though the pictures show the amplifiers uncabled (which they still are), I did manage some sneak listening on the modules and I am looking forward getting these into my main system for a proper test 🙂


Project files: VFET PSU

What is it?
In response to a reader request, the project files for my V-FET PSU board shown here. Of course, this will also work for any other class A design you might think of, as it is a fairly standard CC-R-C configuration with onboard rectifiers and space for three 35mm snap-in capacitors per rail. On typical class A voltages that means you’ll be able to use capacitors in the 22-33mF range and the the onboard rectifiers are 15-25A plastic SIP types, which should be just fine for most applications.

Input and output connections are via FAST-ON tabs and there are two sets of output connections. Since we’re paying for the copper on the boards anyway, I’ve tried to keep as much of it as possible  with a top-side ground plane and the supply rails on the bottom. 🙂

How big are the boards?
The board measures 3.1” x 6.675” (app. 78 x 170 mm).

What is the status of the boards?
Since the prototypes worked fine I haven’t made any changes and the board is therefore version 1.0.

Does it use any special/expensive/hard-to-find parts?
Nothing worth worrying about really. The only possible exception is only really the rectifier which is in a small GBU-package. However, Mouser has them up to 25A (p/n 750-GBU2510-G) and they are available from many other sources in 10-15A variants as well.

Anything else I need to know?

  • If you want to use off-board bridges, bridge the AC and the DC-connections with as thick a wire as you can get through the holes. That should allow you to use offboard metal-cased rectifiers up to 50A. Since the average current draw of most class A amps is quite low and the surge ratings aren’t that different between package types I don’t see the need to use anything else than the plastic ones, but by all means complicate matters with offboard bridges if you must 😀
  • The four series resistors can be 3-5W types in parallel which should be plenty, even if you want to burn off a bit of voltage in them.
  • The (optional) 3W bleeder resistor discharges the two first capacitors while the LEDs will discharge the last ones. The series resistor for the LED can be a 1/2W or 1W type.
  • Last, but not least: Electrolytic capacitors in this sort of size aren’t to be trifled with, so make sure you mount them correctly and test the board properly before mounting it in your amplifier chassis.

Download design files here

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


Pass V-FET kits are here!

Forgot to post this a week ago when they arrived, but I managed to secure a couple of the Nelson Pass V-FET kits which I am quite excited about.

In short, this is a low-power class A amplifier based on some complementary Sony V-FET (SIT) transistors that have been out of production more or less since before I was born. The actual devices were bought as NOS (new old stock) by Nelson Pass himself and offered to the diyaudio community through the diyaudio store as a (more or less) one-off opportunity. I was lucky enough to register my interest early on and so managed to secure a couple of kits to keep me busy on those long Scandinavian winter nights when they come around 😀

There’s a big discussion thread on diyaudio and also an article on the FirstWatt website about the design, in addition to the information in Nelsons previous articles on SITs (also on the FW website). As usual, I don’t really need these and the class A heat is a bit impractical in a small apartment, but a limited-edition amplifier kit with unobtanium transistors that was developed by Nelson Pass himself was an opportunity I simply could not pass up (pardon the stupid pun 🙂 ).

The Firstwatt F5 is still one of the best amplifiers I’ve heard in my system so I have very high expectations for this new design. The lower power of the VFET could be an issue, but I’ll have to build it and try I guess – with my current speakers it should be OK and if not, I can always get a pair of very inefficient planar magnetic headphones instead :D.