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 😉


4 Responses to Surrounded – again!

  1. david weightman says:

    I was intrigued to see your use of various ICE power modules as I too have been playing with those in recent months…125 ASX, 50 ASX BTL and 250 ASP, for various applications in active speakers and sub woofers. I really like the way you can squeeze them into very small enclosures, I have been using the Penn Elcom extruded AL heatsink boxes which are neat and cheap. Best results I got were from the 125 ASX and a Pass B1 preamp built into the same cases. In other cases I have been struggling with ground loops and hum, particularly with multiple amps in sub applications. I used a small input board from Ghent Audio to convert SE to Balanced but have not been able to get that hum free without disconnecting the mains terminal earth. I know that the ASXs are Class 2 isolated but feel uncomfortable not having a ground connection ( I am British so used to big mains voltages) Do you have any advice about earthing with ICE modules and whether some form of input buffer is always essential? Its been fun playing with ICE but I feel that Hypex has a better relationship with the DIY community and provides more information for constructors!!

    • theslowdiyer says:

      Hi David,

      Thanks for your comments. I definitely agree that the 125ASX and the B1 make a good pair 🙂 I like the ICEpower modules because of the high level of integration and because I know the quality of engineering behind them, but obviously there are plenty of other options out there 🙂

      I’ve written in a couple of blog posts that I think there are very few situations where a buffer is necessary (very high-impedance pre etc.) but that it is a mostly good way to tune the sound according to specific preferences. You’ll note that the Hypex “OEM” modules and a few of the other key class D contenders are supplied without an input buffer so that the manufacturer can design one to suit their preferences/applications/whims 🙂

      There are usually some recommendations on earthing to be found in the ICEpower Designer’s manuals if you haven’t seen those yet, but otherwise the only tips I can offer would be to read the excellent articles from Rod Elliot of ESP and Bruno Putzeys of Hypex. I am not familiar with Ghent’s input board, but it should not substantially change anything.

      I agree that Hypex is more geared towards diy’ers but keep in mind that this was always a conscious decision on the part of ICEpower’s management that they did not want to deal with diy’ers. Obviously a lot has happened in the last 15 years but the diy market is probably not where the money is so from a business POV I think it’s hard to fault that logic. If you are a real ICEpower customer I’m confident that the application support is much better – even for the smaller customers.


  2. Benny Thomsen says:

    Great amp you build, and I’m about to build my own version of something similar.

    I have a hard time finding the 50asx btl version of the icepower. All there is on eBay is SE-versions.

    Where did you buy yours..?

    Thanks a lot for a great post.

    Best regards, Benny.

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