Past projects: 6-channel Tripath amp

Well, without time to finish new projects, it’s time to (once again) go digging in the “back catalogue” instead :D

Here is my first DIY multichannel amplifier. This is based on three Tripath boards from Sure Electronics that were “flavour of the month” some years ago. The boards are based on the TK2050 chipset with the output drivers in bridge mode (so up to around 100W output per channel according to the specs). The boards are stock except that I removed the clamping diodes on the input (which protects the ICs from excessive input voltages) and replaced the (small and horrible) ceramic input caps with (slightly better) Nichicon Muse ES bipolar electrolytics. The boards shown here are the first version that was passively cooled, all future versions I have seen are cooled by small fans. The heat sinks get fairly hot (around 50-55C) when the boards are running.

The PSU is a Mean Well USP-225-24. This is a little under-powered for five/six channels if driven at high levels, but I have a small room and even driving the relatively difficult 4 ohm Elac speakers I never had any issues with clipping. I actually have a spare USP-350 PSU that I have planned to put in instead for a bit more headroom. However, since I don’t use the amp at the moment, for now that is just one more point on a very long to-do list :D

I was originally not going to show this until after it’s been rebuilt with the more powerful PSU, but as I am not getting to that anytime soon here are some pictures anyway :)

Past projects: 6-channel ICEpower50ASX amp

In have owned a number of ICEpower-based amps in my time, partly because I think they are great amps that offer great ease of use and a lot of value for the money – and partly because I used to work for the company :D

My 6-channel amp for surround sound is based on three stereo 50ASX modules. Where the “older” ICEpower modules in the A- ASC- and ASP-series were build entirely with “off-the-shelf” parts, except the magnetics, the ASX series modules are built around a proprietary ICEpower controller and driver ASIC chipset. This means the performance is better and the modules can be mechanically smaller.

The 50ASX is the smallest of the range and as the pictures show, these modules are very compact. Two amplifier channels including the switching power supply takes up only 8×11 cm of PCB space (around the same size  as two credit cards placed side-by-side). Power output is a fairly modest 25W/8R and 45W/4R, but the amp bridges to around 170W so the power supply is quite powerful and for normal listening conditions these have more power than you’d think (note that the SE-version doesn’t bridge, while identical in build, the 50ASX modules are hardwire for either SE or BTL operation from the factory).

A commonly cited “problem” with the ICEpower modules is the low-ish 8kOhm (or so) input impedance. Because of that (and because I wanted to try it) I added some input buffers. These are based on the LME49710 opamp with +2 gain and a 51kOhm input impedance.

Soundwise, for a smallish listening room with relatively efficient speakers this is very good. The 50ASX modules are great little amps that sound very open and spacious over the whole frequency range – and surprisingly powerful at the low end as well. The compact size is definitely a plus as well, the 1U enclosure with feet is actually overall around the same size as my surround front-end, an Audiolab 8000AP processor.

I haven’t done very detailed comparisons between the 50ASX amp and its bigger brother, the 125ASX, which I have also used before (here and here). My initial impressions though is that the 125ASX is more neutral while the 50ASX has a slightly warmer character, but since the 50ASX’es in this configuration is buffered while the 125ASXs are only stock, I am not 100% sure of this. I’ll have to do some more “scientific” comparisons one day :)

Anyway, I have a few more of the 50ASX modules in the drawer (including some of the BTL-version) so obviously there are a couple of more projects in the works – stay tuned :)

Past projects: Tripath TA3020 amplifier

What do you do with a leftover transformer? Well, you buy a matching amplifier board for it, don’t you? Yes, even when I built this a couple of years ago I needed an extra amplifier about as much as a goldfish needs a new bicycle, but still – it’s fun!

The base of this is a custom-wound toroidal transformer from toroidy.pl that was left over from another project and a cheap and cheerful amplifier board from ebay. The amplifier board is based on the Tripath TA3020 controller chip and some “high-tech” IRF MOS-FETs. The board has everything onboard and all that was needed was a bit of wiring and some token heatsinks :D The casework should be instantly recognisable to readers of this blog as well, nothing fancy about that at all – Modushop and Schaeffer all the way. The only “blemish” is the RCA sockets which are silver plated – in theory a brilliant thing for both sound and looks, in practice quite stupid because they tarnish badly the moment you turn your back!

This amplifier sounds surprisingly good. It deiivers a much bigger soundstage and much better detail than I was honestly expecting (although I had heard good things about the TA3020 beforehand). The original plan for the amp was to build it, test it and then sell it on if it didn’t work out, but it actually (to my surprise) turned into a definite “keeper”. It has also “survived” the subsequent arrival of both the ICEpower125ASX and the Pass F5 projects, although these both have qualities that the Tripath-based amp can’t match. However, for “good sound on a budget” this is doing a very good job indeed.

Past projects: Pass Labs F5

One of my most successful builds (no doubt thanks mostly to the genius of the designer :) ) is a Pass/Firstwatt F5 class A amplifier.

The F5 design is the work of legendary amplifier designer Nelson Pass and the design was first published in 2008 – mine was built a couple of years later. It’s a low-powered class A design that puts out roughly 25W at full tilt – and around 180W of heat at idle! The amp is a very simple design, but it sounds very good and it has been immensely popular. There must be thousands of DIY-versions of these playing all over the world and supplementing the 100 original Firstwatt-built models sold for retail (read the 6moons review of that here)

For my build, I used good quality “clone-boards” from ebay, not because I like that but because that was all that was available when I started the project. The components are all sourced from more reliable sources than ebay…The one exception to that is the softstart which is a premade unit from ebay as well. This one is working fine, but I have had another one literally blow up in front of me so one needs to be a little careful here…

The chassis is a 4U/300mm “Pesante Disspante” model from modushop and the heatsinks stay around 25-28C above ambient which is fine. The transformers are custom-wound by toroidy.pl which I have had very good experience with for other projects as well.

The sound of this thing is incredibly transparent and with a big, big soundstage (I like that…) and when you first hook it up, you can scarcely believe that something so simple can sound like this. The bass is also very good as long as you don’t push the amp to far, not quite as controlled as the class D amps I have but with more “body” and “presence” to it. In comparison to the ICEpower125ASX-based amp that is otherwise my normal reference, the general signature of the F5 is a little warmer and “fuller” whereas the ICEpower sounds “lean” in comparison. This extra “warmth” really makes my Elacs (that are a touch bright at times) sing.

Right now the F5 is on “summer holiday”, simply because it emits too much heat to be used when it is warm outside, but in the winter I enjoy it immensely ;)

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 :)

Past projects: An office system with Pass and ICEpower

One of the projects I actually use the most on a daily basis is my amp/preamp office system. This consists of a power amp made with an ICEpower125ASX2 class D module and a matching preamp made from a Pass Labs B1 JFET buffer. The setup normally feeds a pair of Elac 310CE speakers from a Pure i20 iPod dock (with a 160GB iPod classic and ALAC-files).

The preamp is battery powered from a pair of 9V batteries which is a great idea in theory, but not so great in practice. I use the amp quite a lot and I have found out that either you spend a lot of money buying new batteries or you spend a lot of time recharging NiMH-batteries – not sure what is worse here actually. At some point this will probably annoy me enough that I will rig something up so I can use an external power supply, but so far I am just enjoying the sound from this pair. They also showcase that even in my less than ideal settings, the Elacs are absolutely superb little speakers :)

In the last picture you can see the system “in situ”. The owl figure (from Züny) is partly filled with metal and provides an important audiophile function – vibration damping :D.

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Past projects: Passive preamps

Every so often I need to test something which doesn’t have a volume control and it always ends up with some half-baked solution thought up on the spot. Rather fed up with this, some months ago I decided to build a couple of passive pre-amps. This is the result, one balanced version and one unbalanced version.

The builds are pretty standard fare (at least for me), with enclosures from hifi2000, connectors from Neutrik and a rear panel made by Schaeffer (Frontpanel Express in the US). The inside of the unbalanced version holds a cheap stepped attenuator from ebay (that works very well by the way), while the balanced version uses a quad Alps RK27. The value in both cases is 10k ohm as is the norm for passive preamps.

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