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 😀

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.


Project files: Amplifier PSUs

Digging in the back catalogue a bit again here.…and found some of my power supply boards that I haven’t published yet 🙂

What is it?
Power supplies for amplifiers, d’oh! 😀 Two basic variants, namely a “class AB” type and a “class A” type. The “class A” type is intended to be used in a CxC configuration with resistors onboard for CRC and pads for a choke to make it CLC. The “class AB” one is a standard unregulated design for class AB or D amplifiers that allows using both small 16/18mm radial capacitors and large snap-in types (up to 35mm). Here there are two versions, one for 2 off 35mm caps (or 8 smaller caps) per rail and one for 3/12.

The picture below is of the large class AB board. It’s actually the board from the previous post that has had some caps mounted in the mean time 🙂

How big are the boards?
The AB board measures 3.55” x 3.9” (app. 90 x 99 mm.) for the standard version and 3.05” x 6.1” (app. 77 x 155 mm.) for the XL version. The CRC board measures 3.15” x 3.95” (app. 80 x 100 mm).

What is the status of the boards?
Both of the “class AB” boards are in v1.0. The “class A” board is in v1.1 as I made a couple of tweaks (including the pads for off board R/L) to my original version. The original v1.0 is the board that I use in my “Green Monstre” amps.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. You can go overboard with expensive capacitors if you want, but even if you have the money to put NOS Black Gates in your power supplies I’d still suggest you spend them elsewhere in the circuit 😀

Anything else I need to know?

  • Unless you are building very small amplifiers I’d recommend that the CRC and the small AB boards are used in dual-mono configurations with one PSU per amplifier channel. The large AB board can be shared across channels for a medium power class AB or D amplifier (meaning anything with a rail voltage up to around 55V and 63V caps).
  • The boards all include LEDs that indicate power and bleed the capacitors when no load is connected (albeit very slowly). The corresponding resistor footprints should be large enough to allow fairly high LED currents but remember to calculate the power dissipation.
  • The CRC board has space for two resistors in parallel per rail, either axial types (up to around 3-5W will fit) or MPC7x radial types up to 5W.
  • The rectifiers are GBU-types which are available from Mouser up to a 25A rating.
  • Input connections for the Class AB “XL” board are via FAST-ON tabs. All other input/output connections are via 5mm spacing screw terminals.
  • The capacitors on the class A-board can be up to 30mm in diameter. Since class A amps tend to get hot, I’d recommend 105 degree types here. As mentioned above, the class AB boards use either snap-in caps up to 35mm diameter or 16/18mm  radial caps with 7.5mm pin spacing.
  • Needless to say, all capacitors should be rated appropriately for your amplifier’s rail voltage.


Download design files here

Related information:
These are very simple circuits, but there’s some god background on PSU design for amplifiers over on Rod Elliot’s pages (under “power”)

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

An unusual clone…

Well, it isn’t actually that unusual when you look at it, but to most audiophiles these days cloning a Harman/Kardon amplifier doesn’t make a lot of sense – they’re nothing special. That used to be different though**. Before Harman became a big conglomerate, took over many other brands and positioned the Harman/Kardon brand as a middle-of-the-road consumer brand, they were actually quite a decent hifi-company. Especially their top-of-the-range “Citation” series became home to a few popular classics.

Small wonder then, than even Nelson Pass had a go at improving of one of these – go and have a look (or download pdf here). Admittedly it was a while ago (1981), but if Nelson’s had a hand in it I think it might be worth trying and so what you see in the pictures is actually a “Pass Citation 12” clone.

As for my contribution here it’s honestly quite limited – I bought the amplifier PCBs som time ago from diyaudio.com user Tazzz who always makes nice stuff 🙂 The power supply is mine though, but it’s just a bigger version of a previous design I did (as I recently upgraded to a different version of Eagle which can do bigger boards than the standard 80×100 mm.), so honestly that’s not much of a contribution either 😀

As the picture shows, I am stilling missing the main PSU caps but otherwise I already have most of the parts I need to finish this. I need an enclosure that fits as well though, so interesting project or not, it’s going on to my (already very long) list of half-finished projects 😀

**Fun fact: My first “real” amplifier and CD-player back in 1994 were the entry-level models from H/K. That set kept me in music for over 10 years and then did another few years of service with my brother when her moved into his own apartment for the first time. Unfortunately I don’t think the entry-level models from H/K of today are the same quality…

Cloning a classic…

I have been looking at class AB amp designs for a while, trying to find a “compromise” between my low-power (but very large) class A and high-power (and compact) class D builds. For some reason very few among the class AB designs managed to “stand out” to me with the right combination of simplicity, compactness and reputation. It’s not that I really had anything specific in mind, I just kept looking at stuff and thinking “naah, that’s not what I want” 🙂

However, one design that did keep cropping up was Rod Elliot’s “Project 3A” (or just “P3A” for short). This is a discrete amplifier with a reasonable power level for normal use and a very simple design. There’s plenty of evidence out there to support that the performance is good and even a way threads to evolve the design (search the “solid state” forum on diyaudio.com)

Rod sells PCBs for the P3A and that would of course have been the easy route, but because I had a specific form factor in mind I decided to “roll my own” 🙂 The end result is app. 70mm square (flat mounting on a 75mm heatsink were one of the key design criteria) and quite compact. My only concession over the original is that I removed the input capacitor. Well, I didn’t actually remove it on this version since there is space for a bipolar electrolytic from Muse or Blackgate, but the main version is intended for having the input cap off-board.

As I wanted a matching power supply I “recycled” the last Gainclone PSU I did but added a second capacitor bank (which just fit on a board that is still constrained by me using the free version of Eagle). Since the P3A runs on 35V rails it is possible to use 50V capacitors and then a reasonable capacitance is still feasible with this PSU footprint – especially in a dual-mono setup. Of course the board has space for normal 35mm snap-in caps as well, but that’s so boring 😀

I have only done this test version of the amp so far and confirmed that it works and that it plays music. (This is also the reason for the transistor pins not being trimmed properly – bias adjustment). That said, I do have a couple of case ideas in mind for this one where the lower heat of a class AB amp will be welcome (or should I say “required”) 😀