Past projects: ICEpower125ASX2 dual-mono amplifier

Another past project, a compact but very powerful amplifier based on a pair of ICEpower 125ASX2 modules. These class D-modules have a built-in switching power supply and are good for around 450-500W when running in bridge-mode as they do here. They also have very impressive specs for dynamic range etc. and since I have  “squeezed” two modules into a 1U case measuring just 230x280mm, this is a small amplifier with a big punch.

This amp was actually the first step in a “quest” to build a compact and high quality fully-balanced signal chain (the second step is the Retro RIAA-stage in the previous post) and I am now looking into building a matching preamp and DAC as well. I haven’t quite settled on the specific designs yet, but a balanced B1 buffer might be on the cards :).

The impressive specs of the ICEpower modules would not matter much if the sound was’t on par though, but fortunately I think it is. I have tried more or less all ICEpower-modules (except the 250ASX) and these are probably my favourite ones. The soundstage is big, there is impressive clarity and detail from top to bottom and of course lots of power on tap. In some ways the amp is a little “lean” in the presentation, so it does not necessarily suit all speakers, but even with the fairly bright Elacs I have the results are very good. If matched with something with a warmer sound signature (such as the Sonus Fabers I have my eyes on…) I am sure it would be really fantastic.

The modules are stock with no additional input buffering or similar, so I am actually also considering getting another pair and experimenting with different input configurations, including the transformer-based option used by many of the “pro” builders of ICEpower-based amplifiers. However, I might spring for a pair of 250ASX’es instead. If anyone has experience with both the 125ASX and the 250ASX please feel free to leave a comment on the differences in sound signature 🙂


8 Responses to Past projects: ICEpower125ASX2 dual-mono amplifier

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  5. Hi, Can you please tell me how to use this amp with a active crossover? Their connectivity diagram shows that the 2 outputs can go directly to LF and HF, but how will the cutover frequency be configured?

    • theslowdiyer says:

      That only works if you have an active crossover on the input which provides two outputs that have LF and HF cutoff respectively. Then you simply connect the HF output to the left input on the ASX and the LF output to the right input (or vice versa). Then you can simply connect the ASX outputs directly to the drivers.

  6. Philip Kerpen says:

    I just came across the post and I am going to build something pretty much identical. I’m going two build 2 four channel amps, with 2 125ASX2 modules in each. I would like to go for a compact build and was thinking of using the Galaxy GX243 230 x 230 x 40 mm cases. Do you think it’s feasible?

    And what about input buffering? I have seen some charts that suggest the low input impedance at higher frequencies results in significant roll-off, and since I will be using these amps for 4-way dipole speakers that might be worth doing.

    Do you have any suggestions or tips and tricks you would be willing to share? This will be my first amp build.

    • theslowdiyer says:

      Hi Philip, I think you can just about get away with the GX243 for just the modules, but there is not much space left over. If you want space for buffers a GX34x chassis is probably better. If it is your first build I would recommend just assembling the amps and get sound before you start experimenting with buffers. Then it is also easier to decide if you think they make a difference 🙂

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