Tools of the trade? (part 1)

I don’t honestly get a lot of tool questions, but in the interest of being prepared I thought I’d write up a bit of experience about what I think is necessary tooling (and which ones are just very helpful) 🙂 This got pretty long, so it’s going to be in (at least) two parts – the second one will follow shortly.

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Another anniversary…

Here we go again! It’s now been seven years since I started writing here and in a few months I should hit 300 posts (!) which I think is pretty good for a hobby project 😀

The past year has been a bit special and a bit weird in some ways, because during 2019 I honestly wasn’t making much progress on anything (too busy with other stuff) and when there’s no progress motivation generally also tends to drop. However, I think it’s safe to say that 2020 so far has managed to make up for it. The last couple of months of corona-enforced lockdown changed the balance a little and so the last few weeks I have done so many things that I think that compensates for the poor showing of 2019 🙂

Having rediscovered the motivation – and the mountain of unfinished work – it looks like we can keep going for (at least) another year! As always thanks for reading, commenting and asking questions – that’s what really makes it worth continuing here 🙂


Happy New Year!

This year’s new years destination is something a bit closer to home – Berlin! Partly because I haven’t been here for a while, partly because I haven’t been here for New Years but I have heard a lot about it from friends and family.

I don’t expect a lot of diy audio related stuff to happen on this trip, but hopefully that means I’ll come back with the batteries fully recharged and ready for more projects in 2020 🙂

As always, thanks to everyone who reads, follows and comments on what I do here and best wishes for 2020.

Bridging amplifiers…

In response to one specific (and several non-specific) requests and questions, here is a little overview of what to be aware of when bridging single-ended amplifiers. This could be either two channels on certain ICEpower-modules (with some particular considerations mentioned at the end) or e.g. two PA100/PA150 chipamps. Note: The following assumes you are bridging two existing amplifiers, either at board-level or two channels on a finished amplifier. If you are designing a BTL amplifier from scratch or connecting an amplifier IC that supports BTL mode, I suggest you look elsewhere (such as the data sheet for the IC) or this Infineon application note if you are designing from scratch.

On a normal SE-amplifier, both the input and output signals are referenced to a common “ground” (“0V” is probably more accurate, but never mind that for the moment). When you connect two amplifiers together for BTL you couple their grounds together and drive the signal inputs separately. That way, one amplifier “pushes” when another “pulls” the loudspeaker and in theory you can get four times the power (= twice the voltage swing) this way, but there are a few caveats to note.

Firstly, in BTL-mode each amplifier sees half the effective load impedance. Since most normal amplifiers don’t double their voltage swing into a half-impedance load, the max. power you really get is frequently less than four times but still higher than the original.

Secondly, the lower load impedance also means the amplifier has to be able to deliver more current, so the “price” of more power is typically increased heat and a higher risk of tripping an amplifier’s protection circuitry. This is also why many commercial amplifiers that can be bridged state the they should only be connected to loads of 8 ohms or more in BTL-mode, because the amplifiers are not able to handle the 2-3 ohm loads that they would otherwise see.

Lastly, on the signal side a prerequisite for more power in BTL-mode is that you feed one amplifier channel an input signal that is out of phase to the other. Only this way will one amplifier “pull” when then other “pushes”, which is how you double the output voltage swing. That means you need a “balanced” signal, meaning a signal with separate hot and cold pins with respect to a mid-point (ground). You can’t cheat and connect the normal SE input signal as hot and cold because that is also referenced to ground and you would have grounding issues (hum/noise).

To get a balanced signal you will have to either use a balanced source or include some sort of SE-to-BAL converter in the signal chain. This converter can be passive (= a balancing transformer) or it can be an active circuit either discrete or simply built from two opamps. Last but not least it can be a purpose-built integrated circuit in the form of something like a DRV134/THAT1646 line driver or a fully-differential opamp like the OPA1632 (examples of both of which are on this site 😉 ).

I honestly don’t know the textbook definition of “fully-differential”, but whereas a BTL amplifier is two separated channels connected together, a fully-differential amplifier at least has a feedback loop which is shared between the two sides. A fully-differential amplifier will usually perform any combination of SE<->BAL conversion you can think of. If you want an unbalanced input you simply ground the “cold” side of the signal, and if you want an unbalanced output you can take it from the “hot” output and ground.

Specifically for the ICEpower amps that allow bridging such as the 125ASX2 and 250ASX2: The principles are exactly the same as decribed above and as showed in the datasheet, but there is a “BTL sync” pin that should be pulled low as well. The reason is that the ICE-amps have load-dependent switching frequencies and the BTL sync pin ensures that the switcing frequencies track each other (with a fixed offset between them), no matter how you load the two channels. This prevents any risk of the two channels interfering with each other, even under adverse load conditions. Would it work without this connection – yes it should, but why risk problems that are so easily mitigated 🙂

I know this post should have come with a drawing or two, but I can’t be bothered to do that now – plenty of “googlable” examples anyway 😀


Another long break since the last post, but to be honest nothing much has happened over the last few weeks. I have been waiting for some PCBs to turn up and have been busy with non-audio related DIY as well. I’ve also added a few new empty boards from eBay to the project pile but that’s about it.

The PCBs I have been waiting for from manufacturing were a simple dual-PSU based on IRM-modules and another Borbely design – hopefully I’ll have those populated in a few weeks so I can showcase them.

I’ve also previously promised myself to resist the urge to take up more loudspeaker projects, but a few weeks ago a MiniDSP PWR-ICE125 amplifier popped op on my local classifieds page at a reasonable price so now that promise has been broken as well.. No concrete plans yet, but one of the things I’ve investigated before is how to do a “soundbar/soundbase”-style active TV-speaker and some DSP-capabilities would come in handy there. I’ll start by looking at the drivers I have in stock and see if there is anything that be used for that purpose 🙂

Oh, and a final moan about parts availability. I was browsing through Mouser the other day trying to find an 7905 regulator in an isolated package. It looks like JRC are discontinuing some of these negative variants, which is a bit alarming. I genuinely never thought I’d see the day where I’d be concerned about availability of things like three-terminal regulators and BC54x-transistors, but here we are. On the plus side, I’ve noticed that some of the newer audio-grade opamps from TI (OPA16xx) are surprisingly cheap (but of course SMD only) so it’s not all bad but in general parts availability for “normal” diy’ers is declining so rapidly that you can either worry, stockpile or both! 🙂


Yes, it’s that time of the year again – the time where this blog celebrates its anniversary!

This time it’s number six and it is of course even more surprising than last time that I’ve gotten this far. The pace has slowed a bit I think, but I’m still going and in all honesty the backlog of potential projects and content is still huge.
So, if you readers promise to stick around I promise to do the same 😀

Until next year, thanks for reading and thanks for your questions/comments and feedback because that is truly what really makes it worthwhile for me to continue posting! 🙂

Trial and errors….

Like most blogs, social media showcases etc. this page is to some extent a massive display of selection bias – you only see the stuff that works, and only when it works. You never (or at least rarely) see the things that don’t work. Because of that, I just thought it would be funny to at least give you a few examples of the memorable mistakes I’ve made during the life time of this blog – along with the lessons I’ve (hopefully) learned from them.

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Happy New Year!

My New Year’s travels are a recent, but by now well-established tradition. This year I am a little closer to home than last year, which is to say in London. It’s one of my favourite cities to visit – much to the surprise of many of the locals I have to say – but there’s tons of stuff to see and do and I really like the vibe of the place (again, to the surprise of many 😉 ).

I’m here for another couple of days and I have absolutely nothing audio-related planned but that is on purpose. That said, I am of course keeping an eye on the local sales ads just in case there is something on sale that I did not know I needed, but that’s about it 😀

Best wishes for a happy new year to all my readers and I hope to be able to bring you more interesting posts in 2019 🙂


A quiet last few weeks here – at least on the surface. Two reasons for that really: 1) With an Xmas-break looming on the horizon the pace at work is picking up a bit and 2) for quite a lot of projects I am in the annoying phase where lots of important work is done, but it doesn’t really look like you are getting closer to a finished product and so it’s not really worth showing here. If nothing else though, it’s nice to have a good pipeline for next year 😉

However, one thing there is always time for is to buy new projects for the shelves 😀 As regular readers will know I have made lots of ICEpower-based projects, but practically nothing with the various Hypex-modules. However, recently one of the new Ncore NC502MP modules came up on ebay and so I pounced on that. The module looks very nice but I need to test it for a while to check the sound (waiting for proper cables at the moment) and then I’ll decide on a suitable enclosure for it. The original goal was to built a custom high-power integrated amp, but I may end up going in a different direction and do a pure power amp instead. One deciding factor will definitely be whether mounting the module on a simple aluminium bottom plate proves to be enough heat sinking, because if the module has to be on a “real” heat sink, then all my current enclosure ideas are definitely out the window!

Soundwise, I still expect that the benchmark for the Ncore to beat (at least in class D) is going to be my trusty 125ASX-based stereo amp and the 700ASC-monos (which incidentally are also among the designs that are I am currently inching closer to completion…)

In search of synergy…

Slightly off-topic post, but I have written a few times about how I think that system-matching is much more important than any “absolute” sound quality, at least as far as enjoying the music is concerned. Well, today was another reminder that I still think this is the case 🙂

A couple of months ago I got new speakers, trading my old (and much-loved) standmount Sonus Fabers for some floor standing Scansonics that offered a bit more low-end slam. I was quite happy with the trade from the beginning and I have absolutely no regrets, but after a time the inevitable restlessness sets in and you start thinking about change (at least I do…). I’ve been running the Scansonics with a simple 125ASX amp on my Harman/Kardon preamp, but just to try it I dug out another ICEpower-amp from my collection, this time based on the older 200ASC-modules.

Although I would definitely still class the 125ASX as the better amp overall, the Scansonics (which are just a little bit bright) immediately benefitted from the more “closed-in” presentation style of the 200ASC, so as usual after initially listening to half a track I started to go through my normal playlist of tracks I know well and just enjoyed listening to some music that I would normally say I know back-to-front already.

To be fair I am honestly not surprised at this, because I saw the same change when I switched from the even older Elac speakers that much preferred the warmer sound of a 50ASX amp whereas the Sonus Fabers really came to life with the more lively presentation of the 125ASX. However, I still think that it’s nice to be reminded once again what really matters when putting a well-rounded system together and of course experimentation is always fun (although it can sometimes be very expensive as well…)