Inching forward…

Another long(ish) break from posting – this time mostly courtesy of some extremely nice late-spring weather and a couple of house-related DIY-projects. Just about the only thing that has moved forward (at least enough to notice) are my ICEpower 700ASC-based mono blocks (which I discussed here). A couple of weeks ago I got the mounting plates I designed for the modules + supporting circuitry which meant I could drill the chassis and start putting some mechanicals together at last.

Some of you may have guessed that this is where my BalBUF design is supposed to end up, but there was a piece missing. A matching power supply to drop the 700ASC’s 15V aux power supply to something more manageable for the OPA1632 (which gets very hot in operation). Because I was running out of space in the enclosure I wanted to use, a key design criteria was that the PSU should be “stackable” with the BalBUF board.

I quickly found what looks like the perfect device for this use – the TPS7A39 from TI – which is a dual pos/neg low-noise regulator with the right specs. Unfortunately, it is also only available in a 3×3 mm leadless package and as my odds of hand-soldering that are pretty much = 0 I dropped that pretty quickly. Instead I went for a bog-standard LM3x7-based design, but managed to squeeze it down to size because of the modest heat sinking requirements.

In a nod to “reusability”, which is something I always aim for where possible, the PSU board includes SMD resistors on the bottom in front of the caps, which means it can also be used with the unregulated supplies on the other ASX-boards such as the 50ASX and 125ASX. This means that you can use the BalBUF with any ASX-module without a separate offboard supply for the low-voltage circuitry, and because the BalBUF and the PSU stack on top of each other it should be very compact. Assuming everything works as expected with the 700ASC when I test it, I’m pretty sure that means I’ve just figured out what to do with my last remaining pair of 50ASX’es 😀

The sketch for the rear panels is also pretty much done, but given that Schaeffer/FPX panel work is getting more and more expensive I have decided not to order the rear panels “blind”, i.e. before I have tested that the monos work electrically. If this weather continues, that might be a while though 😀

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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 😉

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? 😀

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