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? 😀

ice250asx-1

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7 Responses to One amp to rule them all?

  1. Nicely done. I like the flexibility and modularity you’ve designed into this. I like to complicate things so I’d be looking at an Arduino to facilitate preamp functions such as remote source selection, volume control and the like.

    • theslowdiyer says:

      Thanks Daniel 🙂 It actually turned out to be more “modular” than I originally planned. The mounting plates for the ICE-modules are/were mostly for aesthetic reasons and to avoid having to drill many precise holes in the bottom plate (which is steel and harder to work with). Also, the power-out option actually started from thinking about what I could put in the empty space next to the ICExtend-board and then sort of grew from there 🙂

      I agree with the Arduino-option for switching and volume, but the goal was never really to build an integrated amp – just a power amp with more than one input – and so I agreed with myself that a big selector on the front would be enough. Also, there is actually very little space left over in the enclosure once everything else has been fitted.

  2. Walker says:

    This is fantastic. Great work. 🙂

  3. Pingback: Project files: BUF-03 revisited | theslowdiyer

  4. N.R. Morales says:

    It looks like a great project. I’m eager to see how it turns out.
    A few questions:
    – According to the manual on on the IceXtend, it can only power on three amplifiers, and they must be all from the same series? So you can’t say mix 125asx2 and 250 asps? But you can hook up a 125 asx2, and a pair of 50asx2?
    – An input buffer maybe needed on all ice modules, but it doesn’t appear that it’s always implemented in all commercial designs. What are your thoughts on this, or does it vary from series and the source that you will use.
    – Is the drop across the audio spectrum that’s causes the need for an input buffer due to what I understand is an impedance mismatch occur in an consistent fashion such that it could be eq’d by something like a min-idsp/mini-sharc?

    Also, I love your blog. Keep it up.

    • theslowdiyer says:

      Thanks. Progress has been a bit slow on this project, but the front panel for the amp is just about due and then I am very nearly out of excuses to start cabling it 😀

      To your questions, which are definitely not easy to answer:

      1) Yes, the ICEextend has three connections for power out. I don’t think there’s anything technical that dictactes that the connected amps have to be from the same series, it’s probably just that applications combining different modules are rare and so they’re not shown.

      2) Whether the buffer is needed or not is mostly subjective in my view. There are some preamps where you can say it is necessary, but that is definitely a minority. For everything else I’d say that you can use a buffer to influence the sound so that it becomes more what you want, but it is a question of preference.
      Whether the designers that do not add buffers are lazy, uninformed, incompetent or just people that have tested and drawn their own conclusions I’d rather leave up to everyone to decide for themselves 😉

      3) Quite difficult to answer, because I don’t think there’s necessarily one single answer to what an impedance mismatch does to the sound. The short answer is probably that yes, you could accomplish the same change in sound signature using a DSP-based EQ, but you might struggle a bit to actually figure out what to dial in.

      Not an expert on this by any means, but that’s how I see it. Thanks again for your kind words 🙂

  5. Pingback: Surrounded – again! | theslowdiyer

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