Past projects: 6-channel ICEpower50ASX amp
August 25, 2013 12 Comments
In have owned a number of ICEpower-based amps in my time, partly because I think they are great amps that offer great ease of use and a lot of value for the money – and partly because I used to work for the company 😀
My 6-channel amp for surround sound is based on three stereo 50ASX modules. Where the “older” ICEpower modules in the A- ASC- and ASP-series were build entirely with “off-the-shelf” parts, except the magnetics, the ASX series modules are built around a proprietary ICEpower controller and driver ASIC chipset. This means the performance is better and the modules can be mechanically smaller.
The 50ASX is the smallest of the range and as the pictures show, these modules are very compact. Two amplifier channels including the switching power supply takes up only 8×11 cm of PCB space (around the same size  as two credit cards placed side-by-side). Power output is a fairly modest 25W/8R and 45W/4R, but the amp bridges to around 170W so the power supply is quite powerful and for normal listening conditions these have more power than you’d think (note that the SE-version doesn’t bridge, while identical in build, the 50ASX modules are hardwire for either SE or BTL operation from the factory).
A commonly cited “problem” with the ICEpower modules is the low-ish 8kOhm (or so) input impedance. Because of that (and because I wanted to try it) I added some input buffers. These are based on the LME49710 opamp with +2 gain and a 51kOhm input impedance.
Soundwise, for a smallish listening room with relatively efficient speakers this is very good. The 50ASX modules are great little amps that sound very open and spacious over the whole frequency range – and surprisingly powerful at the low end as well. The compact size is definitely a plus as well, the 1U enclosure with feet is actually overall around the same size as my surround front-end, an Audiolab 8000AP processor.
I haven’t done very detailed comparisons between the 50ASX amp and its bigger brother, the 125ASX, which I have also used before (here and here). My initial impressions though is that the 125ASX is more neutral while the 50ASX has a slightly warmer character, but since the 50ASX’es in this configuration is buffered while the 125ASXs are only stock, I am not 100% sure of this. I’ll have to do some more “scientific” comparisons one day 🙂
Anyway, I have a few more of the 50ASX modules in the drawer (including some of the BTL-version) so obviously there are a couple of more projects in the works – stay tuned 🙂
theslowdiyer 
I saw this build on diyAudio & was immediately attracted because I am about to build my sister some active speakers & have just purchased some 50ASX2 amps to power the speakers. I have just finished reading the manual & was starting to research buffers!!! I was wondering if you had any buffer boards you would be willing to sell me?
Hi David,
I have no spare boards of this type, but I might be able to help you with design files etc. I will reply to your PM directly.
/U.
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Hello
I love the quality of your work
I’m looking at a similar project – I’ve settled on ice power as It combines the power and amp in a nice small package and people seem to be happy with the sound
I want 8 channels (to act as 4 zones) to power a multi room audio system based driven by airport expresses
I’m going to use either 4x 50asx2’s in se mode, or 4x 125asx2’s. Given the amp will be on 24×7 I’m going to use two icextend modules (driving to amp modules each) to give me 0.5w standby
One last piece of the jigsaw is whether I need input buffers – it mentions them in the design manual I’ve seen, but I’ve seen implementations both with and without – could you email me and advise?
Thanks
Hi Chris,
Thanks for you comments. It sounds like an interesting project you’re working on. I haven’t ever used the ICExtend modules, but they look useful, especially for an application such as yours. I actually also have a couple of projects in the pipeline where they could be used, so if you know of a source for them I’d be very grateful if you could send me a note 🙂
Normally I think people use the input buffering of the ICEpower modules to tweak the sound to their liking – at least that’s what I do ;). There’s only really two scenarios where you need an input buffer stage:
– One is when the source (preamp) has high output impedance and low drive capability – this normally translates to either passive pres or tube ones (if they aren’t designed for low output impedance). Here you need the buffer to match impedances, but not to provide any gain.
– The other case is when you are driving the amp with a very weak source and need to raise the level. Here you may need the impedance matching that the buffer provides, but you also need a bit of extra gain.
If your application is a multiroom system I assume you’ll be driving the ICEpower modules from a multiroom capable source (preamp/processor or similar) and in that case I doubt you actually need a buffer at all. However, you could of course plan for having it, ensure there is space in the chassis for buffer boards and a small extra power supply and then try without them first. That way you could also tweak the sound later on if needed.
Let me know if you have more questions 🙂
/U.
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Hi,
I’m wondering which power supply have you used to drive opamps? Is this something of-the-shelf or DIY? Which transformer does it use?
It’s a DIY design of my own, a very simple design with 78xx regulators. The transformer is rated 2.8VA so it will not output more than app. 80mA per side which is just enough to power the opamps, but for this application it is fine.
Thank you, I was asking about particular part number for the transformer if possible. I imagine it’s some 24VCT? My knowledge of EE is very limited and I’m trying to assemble working amplifier from off-the-shelf 50ASX unit and a buffer board, but I lack +-12V power supply for opamp.
I assume the buffer board takes AC-power from the transformer and not just DC (or that you have a PSU in the middle)? Anyway, the easiest way to find these small transformers which are made by many manufacturers is to search for “EI30” or “EI38” and look through the results. This is technically the only size of the transformer core, but it’s normally included in the part numbers. EI30 is the size I used here and EI38 is the next size up. For a 12V PSU you need a 2x12V transformer.
thank you, it took me some time, but I guess I figured it out. And you were right, I just need the transformer. The rest (diode bridge, voltage regulators, capacitors) are already available on the buffer board.