50ASX BTL conversion (part 2)…

So, I’ve done some more testing on my BTL-converted 50ASX-modules…

As you can see, I’ve used a slightly less improvised test setup compared to last time (it looks worse than it is…). While I wouldn’t call what I have done “extensive testing” by any means, my gut feeling is that this works 🙂 It also ties in well with how the other ASX-modules work and some “insider knowledge” from years ago that I can still recall 🙂

Note and disclaimer: I would very much appreciate if someone else tried this to verify and maybe do more testing, however I will accept no responsibility for damage to property, people or pets (or anything else for that matter) if you find a problem – this is DIY after all 😀

You can of course hack this conversion anyway you like, but I opted for removing the old jumper altogether and soldering in a new one. If you do that, be advised that the ASX-board is four layers and soldered with lead-free solder, so it will take a bit more heat to reflow the joints than I am at least used to. If you use a soldering iron that is too small, you’ll just heat up the board and possibly damage it.

My suggested approach would be to cut the jumper on the top side of the board. Heat the solder joint from the bottom and pull out the jumper wire with small pliers. Then clean the remaining solder off the board with desoldering braid or (better yet) a vacuum desoldering station if you have access to one. Then solder in the new jumper in the BTL position. There isn’t much space to work on and you should be careful not to damage any of the (sometimes annoyingly) small SMD-components on either side of the board. Once the new jumper is in place, follow the wiring diagram for the BTL-version in the 50ASX data sheet/designer’s manual and you should be good to go.

Bear in mind that what you end up with isn’t a “real” balanced (= differential) amplifier, but two SE amps referenced to ground and driven with opposite phase input signals to produced a bridged output. As such, the input ground is still required in order for the amp to produce a correct signal on the output. I’ve found a good sketch here for LM3886 modules that should show the correct input wiring. Output on the ASX is taken from the P104 connector, so ignore what the sketch shows here (and of course the DC wiring is irrelevant as well).

If you do try this, let me know how you get on 😀

PS: Yeah and the picture is still crap – but don’t worry, the light should be better from around April onwards 😉


ICEpower 50ASX – SE to BTL conversion

I’ve recieved a few questions (and participated in a diyaudio discussion thread) about converting ICEpower 50ASX2 SE modules (which are fairly easy to get), into 50ASX BTL modules (which aren’t). I was pretty sure this could be done without component substitutions by simply desoldering the W401 jumper and resoldering it into the W400 position (marked BTL on the bottom of the board) but as I had no modules left, I couldn’t try it. Now I’ve managed to get my hands on some more modules and I’ve actually tried converting one of them and the good news are – I think it works!

I haven’t actually measured anything (not sure what to measure to be honest) but I get clean audio out on the BTL speaker connector (P104) and a very loud buzzing noise on the other output, so at least it isn’t running stereo anymore. No guarantees on anything yet though, but it’s definitely promising.

Oh, and don’t laugh at my improvised test setup, it is necessary because I don’t have a proper balanced source in the house at the moment and I couldn’t be bothered to crimp new cables just for testing 🙂 Incidentally, don’t laugh at the poor picture either – winter in Scandinavia means the days are so short that I can only take pictures in daylight during the weekend…

Next up is to convert a second module, build some better cables and try it “for real” in a stereo setup – hopefully this weekend 🙂


Project files: ICEpower integrated amp board

What is it?
The project files for the “all-in-one” (nearly…) PCB for making integrated ICEpower amps shown in the previous post.

How big are the boards?
The board measures 2.65″ x 3.15″ (app. 67 x 80 mm.).

What is the status of the boards?
The board is version 2.1. As mentioned, it’s an old design that I have revised and updated to give it the 2.x version number. I’ve built my prototype on a v2.0 board and made some minor tweaks to that before publishing.
The changes in v2.1. are mostly mechanical (too little space for the input connectors etc.) and then minor touch-ups to the silk screen.

Does it use any special/expensive/hard-to-find parts?
No. The overall circuit is quite simple and only a few parts require a bit of attention.

  • The relays are standard mid-sized “2 form C” contact types. If you’re buying from scratch I’d recommend the Takamisawa RY-12W type, but there are app. 1 million equivalents with similar specs and footprint, so you may be able to get good surplus deals as well :). The coil voltage must be 12V.
  • The voltage regulators are standard 7812/7912 types but as they are mounted very close together I recommend the fully-insulated versions. I prefer the ones made by NJR as opposed to ST because the ST-ones seem to behave a bit strangely sometimes (and yes, I might be imagining this…).
  • See BoM-file for description of other parts and values.

Anything else I need to know?
A few things:

  • The on-board parts draw no current from the negative PSU rail. If you’re not using any external circuitry you can omit the negative rail (regulator etc.). If you build it anyway and get strange results, note that some regulators do not like a “no-load” condition and will give an weird unregulated output if not loaded. You can solder a 1-3k resistor on the bottom if you want for added peace of mind.
  • ASP/ASC-usage: It’s possible to use the board with ICEpower ASC and ASP modules. As these include a regulated +/- 12V AUX supply, you should jumper the regulators and the input resistors. The capacitors and remaining components can be left in.
  • Mute-header: The Mute-header simply brings the two pins required for the module’s mute or standby pins to work to a header at the from of the board to simplify wiring. Refer to the datasheet for the respective modules for details on how to use this, but in general you can switch using a mechanical switch.
  • Heat sinking: There is no heat sinking of the regulators as standard. With a simple preamp and no additional load this should not be necessary, but if you want to draw more power then use a small bit of metal as the heat sink. There is not much space in either direction, so using insulated regulators will once again be an advantage.
  • If you prefer a manual input switch, the board is just about ready and will be presented as part of another project post in a few weeks 🙂

Download design files here

Related information:
Please read the FAQs in the original post as well. The picture below shows my “in progress” prototype amp with the Minipre and a 50ASX-module and gives an idea of the expected layout.

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



Simplifying ICEpower integrated amps…

Another old idea that I have resurrected and polished up a little 🙂

Many people (and many of my readers) want to build small integrated amplifiers with ready-made amplifier modules, e.g. the ICEpower ASX-series. It’s not that difficult as-is, but what if there was a single board that could help to convert an ICEpower ASX-module into a proper integrated amp? Well, there is now 😉

This module is basically made up of three parts bolted on to the same PCB.

– four single-ended inputs, switchable with relays
– a selector circuit that enables input switching with a single pushbutton (or with a rotary switch if you prefer)
– a power supply to utilise the on-board (but unregulated) AUX power supply on the ASX-modules as a power source

The only thing missing here is a pre-amp of some sort which must be a separate PCB, but can be powered from this board. The “Minipre” circuit was specifically made for this job but other circuits would certainly work as well – as long as they can run off +/-12VDC.

I made the first iteration of this board several years ago but managed to mess up the power supply arrangement so the original version didn’t really work (grr!). That I decided to get this circuit out of the drawer quite recently is no coincidence – I happened to find a single 50ASX module which I thought I had used already and so you can probably guess where this will eventually be going 😉

PS: While I prepare the project files for publication, let’s take the most obvious Q&As straight away 🙂

Q: Can it be used with other ICEpower modules, e.g. ASP/ASC-models?
A: Yes, but you’ll have to bypass the onboard power supply regulators etc. on the selector board as the ASP and ASC-modules have a regulated AUX-supply. Also, this board is intended for SE inputs and not balanced inputs (see below).

Q: Can the board be used as a standalone circuit or with other types of power amp modules?
A: Yes, but you’ll probably need a small unregulated dual power supply (15-18V) to power it. The current requirements will depend on which preamp-circuit you are using, but around 100-200 mA should be enough.

Q: Do I need to be able to program microcontrollers to build this?
A: No, the input switching is based on a 4017 counter IC so there is no code in this project at all.

Q: Can I use a rotary switch to select inputs?
A: Yes. Just connect the switch to the I/O header and omit the 4017 IC and its supporting components (a dedicated PCB for this is coming very soon).

Q: Can I stack two boards for balanced inputs?
A: Probably, although I haven’t tried it. Build a full “master” board and then a separate “slave” board without the PSU and selector components. Connect the I/O headers between master and slave for power/control and it should work (again, note the “should”-part…).

Surrounded – again!

This is an old project that I have resurrected now as I would like to get my surround-sound setup back into working order (not that I expect I’ll be using it that much, but still…)

It’s a 2+3 channel ICEpower ASX-based setup with 125ASXs in BTL-mode at the front and 50ASXBTLs for center and rear. The 2-channel amplifier very nearly identical to my previous 125ASX-based amplifier but it does have three USPs compared to that build:

  • Transformer-coupled (balanced) inputs using Lundahl LL1527 transformers.
  • Two switchable inputs so it can be connected to both a stereo source and a surround-processor simultaneously.
  • ”Audiophile” form factor (i.e. around 44 cm. wide and much larger than is really necessary 😀 )

The 3-channel amplifier also has Lundahls at the input but no input switching (for obvious reasons).

Many upmarket manufacturers use transformers on the inputs of ICEpower-based amps and Lundahl in Sweden make some of the best ones around. The LL1527 isn’t usually employed as an input transformer, but if I’m reading the specs correctly it’s actually fairly well-suited to the lowish input impedance of the ICEpower modules so it should work well. The alternative (which would also fit on my boards) is the LL1540 which is a purpose-built high impedance input transformer. And well, if all else fails the way that these are mounted would mean that I could probably develop an active circuit instead 🙂 (differential opamp-board anyone?)

Just like my as-yet-not-completed “Ring” amp project the front channel amp has switchable inputs so that it can be used in a combined stereo/surround setup. Switching after the respective volume controls make more sense to me, but of course I haven’t actually lived with it yet so let’s see if theory meets practice in this case 😀 This switching is relay-based and uses the balanced selector modules I posted about earlier – yes, sometimes those piles of leftover prototype PCBs come in very handy :D.

There isn’t actually a lot missing – mostly cabling – before this is done, but I hate cabling so it might take a while to do it anyway 😉

Past projects: Old ICEpower Amps…

I’ve built quite a few ICEpower amplifiers over the years, but many of them were built and sold before I started this blog. Recently I actually saw an amp for sale that I am pretty sure I built and so I started looking to see if I had any pictures of these amplifiers. Mostly I don’t, but I did manage to find a few:

The first amp is a small amp based on a 200ASC-module with a 200AC hanger. Unlike the ASP and A-series, the amplifier sections on the AC/ASC are the same so it is possible to build a (deceptively compact) stereo amplifier this way. I used this amplifier in my office system before I eventually replaced it with the B1/125ASX combo.

The second amp is a full-size amp based on 2 pcs. 1000ASP-modules. At the time, this was intended to be my own reference amp, but firstly I preferred the sound of the 500ASPs I were using before and secondly I got a very good offer on it so I decided to sell it soon afterwards.

The last amp is a three-channel model with a single 500ASP and a pair of 200AC hangers. The amplifier I used for a couple of years to power the center and rear channels. As the front amplifier I had two stereo amplifiers with dual 500ASPs wired in bi-amp mode, which made for a very compact surround system with plenty of power – around 3kW into 4Ohms – on tap :D. I eventually sold all these amps and started using the 6-channel 50ASX instead.

Project files: ICEpower Linear PSU

What is it?
The project files for the linear ICEpower PSU board I showed here. The first version of this board concept was made around 10 years ago, but as I didn’t have any boards left over I updated the design and cleaned it up a bit in the process.
The basis of this is once again the GP-PSUs shown here and the same file that I also used in a triple-configuration here. I have simply added a single high-power rail with a rectifier, two main caps and the usual decoupling + discharge LED – absolutely nothing fancy 🙂

How big are the boards?
This is the “XL”-version for 35mm main caps and the board measures 4.4” x 3.45” (app. 112 x 88 mm.).

What is the status of the boards?
The design is called v2.0 as it is based on a previous idea. It’s been prototyped and I see no mechanical or electrical issues.

Does it use any special/expensive/hard-to-find parts?
Not really, unless you choose to go overboard with expensive boutique parts, such as premium capacitors and fast rectifiers for the low-voltage supply (which I kinda did…).

Anything else I need to know?

  • The board should work with the ICEpower 200AC/300AC and the 250A modules which require around a 50VDC Vp voltage. For the 500A and 1000A modules you might need to check and modify the board files to get enough high-voltage clearance for the higher supply voltages used (nominal 80VDC/120VDC respectively)
  • The high-power supply uses a pair of snap-in capacitors up to 35mm in diameter and a GBU-type rectifier (available up to 25A). The low-voltage supply uses 22mm snap-in or 18/16mm standard radial caps with 1N540x or similar rectifiers.
  • Due to the rectifier setup on the low voltage supply, it is possible to use it with both single (voltage-doubled) and dual AC connections. In that case you should connect the transformer to one side of the AC-connector and you need only fit the required pair of diodes (either DA/DB or DX/DY), although of course there is no harm in mounting both pairs.
  • If you have space, I would recommend that you run “dual-mono” with separate power supplies for each channel, mainly to ensure that there is a good amount of capacitance on the high-power rail. If, like me, you still want one box and avoid a true mono-block design, then the high-power rail can use separate windings on the same transformer and the low-voltage transformers can be separate or shared between the channels. The sharing can of course be done either as parallel-connected dual rectifiers or as separate voltage-doubled circuits with each board using one transformer winding (honestly not sure what would be better here 🙂 ).

Download design files here

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

Read the ICEpower module datasheets carefully as well (and, if you can get your hands on them, the Designer’s Manuals as well).

Note: For once, I do actually have some spare boards left as I only needed the pair and I had to order 10 pcs. As you can see, they are green, HASL-plated and made with 2 oz. copper. If you are interested in boards, drop me a line.

ICEpower 200AC Amplifier

A while ago I realised I still had a single pair of ICEpower 200AC modules left over as well as a suitable transformer – and why miss an obvious opportunity to make another power amplifier I don’t really need? 😀

The 200AC module is exactly the same amplifier section as the better-known ICEpower 200ASC only without the onboard power supply. The 200AC board is very compact at app. 55 x 107 mm per channel but will still put out over 200W into 4 ohms and because I had the transformer available I opted for a linear power supply. The transformer is a custom one I got from ebay (I think) with a 32VAC winding and a single 12VAC winding. This makes it perfect for the ICEpower modules as the dual-rail low-voltage supply can easily be generated via a voltage doubler. The main power rail is a bit lower power than I might have wished for (160VA), but not overly so, and the transformer is made by what I consider a quality manufacturer so it should be OK. 160VA is still more than 1/3 of the peak power which should work as a rule of thumb (yes, I know it is a bit more more complex than that but a good starting point as far as I am concerned).

The power supply board is a variation/update of a design I first made nearly ten years ago (when I started building with the ICEpower modules) and quite simple. I will publish the board files shortly as it might be useful for other users of the ICEpower AC-series and A-series modules without switching PSUs. I’ve used a dual-mono setup with separate PSUs mainly to be able to add a bit more capacitance to the mail supply rail (2 x 10000uF per channel) which shouldn’t hurt. The capacitors are very audiophile-approved “Gold Tune” types from Nichicon, not because I think it is audible per se, but because I like the look (yes I know, I shouldn’t admit to such things :D)

Apart from the amplifier boards and the power supplies I have added fuses on both the primary and the secondary sides of the transformer via a couple of my supporting PCBs. The secondary-side fuse board is the one I published here and the primary side fuse board is somewhere in the pipeline :). Obviously using these boards aren’t strictly required, but I wanted the fuses in the amp and especially the secondary-side board also makes for much neater wiring than would otherwise be possible for me to achieve.

I also wanted this amp to be fairly compact and unfortunately that took a few bits of custom metal work to achieve, namely a mounting plate for the modules and PSUs, another for the transformer and a small one for the primary fuse board (not fitted yet in the picture below). That obviously pushes the cost up a bit, but fortunately I have decided to ignore that part 😉

The back panel sketch is done and will be included in my next order with Schaeffer/FPX. Still to do is a front panel and some wiring, although I might actually hold off doing the front panel until later. That way I can match the looks of this power amp to an as-yet unspecified DAC/preamp/whatever to make a matching set 😀


Project files: BUF-03 revisited

What is it?
As I mentioned in my post on my still work-in-progress “Ring” amplifier, I am planning to use (at least initially) a version of my BUF03-buffer as the input stage. Since I have now build and tested the revised boards and they seem to work well, I thought I’d publish the files as an update to the original. Key changes are:

  • In/Out connections are now grouped together as single 3-pin headers instead of the previous 2 x 2 configuration.
  • PSU connector has been uprated to a screw clamp type which is easier to work with. Also, there is now only one PSU entry instead of two.
  • The diameter of the decoupling electrolytics has been reduced to 8mm which should still be plenty for low-ESR types (Panasonic FC/FM are what I normally use). The smaller caps make the board look a little less cramped.
  • There is now a provision for a resistor at the input. This sets the input impedance and may be useful in applications where no volume pot is used. It is optional if you either want to use a volume pot immediately before the buffer or just want the previous stage to see the natural input impedance of the BUF03 (which is quite high).

How big are the boards?
The board measures 2.55×1.45″ (app. 65x37mm) – same as the original.

What is the status of the boards?
The board is now in rev. 1.5 as I’ve only made minor changes (described above). Both the original version and this one have been tested and work fine.

Does it use any special/expensive/hard-to-find parts?
Yes. The BUF-03 IC was discontinued several years ago. They are often available as used or NOS on ebay, but as always be wary of the risk of counterfeit/substandard parts in ebay listings.

Anything else I need to know?

  • DO NOT attempt to use this board with the BUF634 or any other buffer IC as that will not work.
  • The BUF-03 ICs are internally biased to class A and will get (quite) hot during normal operation. Small TO-5 heatsinks are recommended if you can find them.
  • The board can be used with the (equally hard to find) BUF-04 from Analog Devices, as long as you note the different pinouts (different location of the DC offset adjust pins).
  • Remember to measure and adjust the DC-offset with the inputs shorted, preferably like this: Apply the power, measure offset and adjust to zero with the trimmer. Once done, disconnect power and let the buffers cool down. Once they are cold, reapply power and check that the offset does not “drift” too much when they heat up (leave them on for 5-10 mins. at least).

Download design files here

Related information:
See the two original posts for some more information and links.
Note: Always read the “intro post” for additional important information about my designs.


One amp to rule them all?

After years of experimenting I am slowly getting an idea of what the “perfect” power amp for me looks like. Not so much in terms of sound because that will always be an issue of system matching, especially to the speakers, but more in terms of feature set. So, for the last couple of months I have been planning a new amp design that when finished could be the only one I need – maybe it should be called “The Ring”? 😀

The power amp section is comprised of two ICEpower 250ASX modules in BTL-mode which should make them good for around 600W output. I have never tried the 250ASX-modules before so it is a bit of a gamble that I like them better than the 125ASXs, but worst case the mounting plate design means I can make them fit anyway without having to drill into the enclosure again. The power is provided via an ICExtend-board – another first for me – but it looks very useful.

There’s input switching which comes courtesy of a 3-way version of my relay selector board. This should make it possible to use a stereo analogue setup with a RIAA and preamp, a stereo digital setup with separate DAC and also a surround-setup with the main speakers acting as fronts – without having to switch any cables around. Since the switching happens after the volume control stages there should be less risk of equipment or ear damage.

The relay selectors are powered by the AUX-supply on the ICExtend board that also distributes power to the ASX-modules and enables having both 12V- and 3-5V logic level trigger inputs on the back.

To facilitate some experimentation with the sound, the input section will be able to use a few different designs, namely the discrete Alpha20 buffers from AMB, my own simple op-amp buffer, AMBs new fully-differential Alpha24 or a slightly modified version of my BUF03-design. I am honestly not sure I need that much choice, but since the mounting holes are the same size they all fit 🙂

In addition to the input switching and buffer options I have included a “Power Out” option that could potentially be used to power a source and/or a preamp. Since I don’t know what is required here the power board has universal hole pattern and will fit anything from a standard 30-40VA toroid though a board-mounted transformer to a single board-mounted Mean Well IRM-series SMPS. The rear panel output for the power out is a Neutrik D-series hole that is fairly universal in itself and most likely I’ll start off with a 5p female XLR to ensure nothing is plugged into the power out by accident.

A couple of things missing obviously: I need new boards for the modified BUF03-stage which I’d like to try first, but due to Chinese new year it’ll be a couple of weeks before I can order boards and then another couple of weeks before they actually show up. I also need to assemble and test the PSU boards and while I already have the rear panel, I am missing some of the connectors etc. so we’re not quite there yet 😀

Oh, and just in case any regular readers were wondering: No, I don’t really believe I can settle for having just one amp at my disposal but it is a nice thought, right? 😀