More JLHs…

Yeah I know, I should probably stop making these at some point 🙂

We’ll do this one quickly then: Standard JLH1969 Ebay-board with upgraded components and better transistors (MJ15003). Fan-cooled heat sink with temperature control (we’ll see how well that works…). Industrial-grade 10A switching PSU per channel. Monoblock configuration in Modushop GX288 chassis.

The PSUs (Artesyn NLP250) are overkill for this application but they were cheap (surplus items). And besides, more is better – right? Not necessarily here though, because some of these industrial-grade PSUs have a reputation for being extremely noisy at low power output. As a class A amp, the max. current consumption of the JLH should be twice its quiescent current (so app. 2.6A) and each PSU will deliver four times that before the limiter kicks in. Whether this is a real problem here or not I don’t know yet, but there are no audible artifacts at all so I am not overly concerned right now.

The heat sinks were also surplus items and I am not sure exactly what their rating is. At full speed the fans are a bit too noisy for my liking (the heat sinks add some flow noise as well) but if the fan speed is lowered a little I don’t think it would be really noticeable once the amps are seated in a rack. For the time being I have installed some small temperature speed control boards for the fans (hence the somewhat messy wiring) but depending on how well that works and how hot the amplifiers get, I may go back to fixed resistors. The PSU already has a dedicated 12V fan output so the resistor doesn’t need to drop a lot of power.

The heat sinks had a cutout in the side that was just too narrow for the angle brackets to fit into. The best solution would have been to mill the ends of the brackets to fit the cutout so there is only one contact surface. Unfortunately I don’t have access to a mill anymore so I had to find another solution: A copper “heat slug” to fill the gap. Just a piece of copper bar in the right thickness cut to size and with thermal grease on both sides and that should provide the best possible thermal transfer under the circumstances.

So, will I stop building these amps? Erm, no! 😀 I am out of the ebay-boards but I do however still have my own version of the 1969 JLH that isn’t cased up yet. This build has given me some inspiration for how I can build that into small monoblocks so while it might take a while to do at least I know what parts to keep my eye out for 🙂

Mini-stack (part 1)

Not exactly the most challenging builds ever undertaken, but still…

More or less since I originally built my passive preamps I have wanted to build more components in the same form factor. Here is the beginning of a “mini-stack”, namely a USB DAC and a passive pre, which should then be supplemented later by (at least) a power amp in the same small chassis (a GX143 from modushop.biz, so 124x40x73mm). That isn’t ready yet, but I do have a few ideas for what to do 😀 As for what is ready:

The passive pre is based on a Noble 10k pot that I happened to have lying around – not much more to say about that really 🙂

The DAC is based on an “off-shelf” module from ebay. It uses the SA9023 USB receiver/ES9023 DAC chipset so that it can accept up to 24/96 input signals. The module is powered from the USB connection. It is possible (and possibly recommended) to use an external supply instead, but since the preamp is passive I wanted to keep the design “cordless” except for the USB. Obviously that won’t work for the power amp… My only little piece of hacking here was to wire an “USB on” LED on the front panel instead of relying on the on-board SMD one.

The ES9023 DAC chip from ESStech is a highly respected performer and used in quite a few designs such as the AudioQuest DragonFly (albeit there with a more complicated/advanced USB front-end) and quite a few others. It is voltage output with a built-in charge pump to avoid capacitors in the signal path and it is actually capable of driving headphones directly, so the 10k load here isn’t really an issue.

The sound quality of the board is quite a bit ahead of the older PCM27xx-based designs as well. The sound from this little combo is actually quite good and the fact that no external power suppliers are required makes it a bit more interesting.

My idea for the power amp is to use a class D chip powered from an off-board switching supply. I have looked at both the TPA311x and the TDA749x chips but I am still exploring options here so nothing definite yet…let’s see what happens 🙂

WCF amp completed

It’s been quite a while since I really finished a build. Sure, lots of small steps forward on lots of other projects, but nothing really finished to that fantastic moment where you can actually hear music for the first time 🙂 (or the slight less fantatic moments where you see smoke, a broken fuse or simply nothing at all… 😀 )

This is the just the WCF headphone amp I build a while ago (see this post) which has now been cased up. Instead of putting in a lot of effort on DIY mechanics I took a shortcut and bought the bespoke ebay-chassis for the design. It’s not bad, obviously fit and finished has been seen better, but given how I normally struggle to do the mechanical stuff it was still worth it. And anyway, this was a bit of a “sideline” project anyway. The transformer is from Audiophonics because they had an “off-the-shelf” model with the right specs which also was about half the price of a custom one from Toroidy.

Listening at the moment with a newly-purchased (but second-hand) Arcam rDac as the frontend and this amp is still not bad at all for the modest outlay I think 🙂

Waiter, more ICE please!

After building the 6-channel amp with the ICEpower50ASX modules my stock of modules still wasn’t depleted. Time to fire up the imagination then…except not a lot of imagination was needed to come up with this to be honest 🙂 It’s a very simple miniature poweramp in a small Modushop enclosure (cabinet dimensions excl. terminals, feet and front panel is around 130x175x40mm).

The main point of this build is small size but of course that makes the layout fairly cramped. The amp works fine as it is, but there are a couple of issues which I plan to rectify in an upcoming “v2”. Firstly, the mains switch is a bit small, in fact so small that the inrush current from the switching supply causes it to “stick” quite badly. Secondly, I have reversed the position of the left and right outputs compared to what you normally see. While it makes for slightly neater wiring on the inside, it makes for ridiculously impractical wiring on the outside (trying to cross a pair of stiff speaker cables) so that has to go as well.

Soundwise, this is quite good. From my recollection, the 50ASX is the “warmest” sounding of the ICEpower modules which is quite nice, and there is enough power on tap here (app. 50W into 4 ohms) to supply my speakers at normal listening levels. I have a matching Pass Preamp in the works as well, and with those two I actually think that is all anyone really needs from a sound system (not that this will stop me from building more gear obviously :D)

Resurfacing…

Things have been quiet here lately as real life once again intrudes on my build time 😉 I did however manage to finish one small project over the last couple of weeks, a clone of the Grado RA-1 headphone amplifier. Well, “clone” is maybe stretching it a bit – maybe it should be “inspired by” instead 🙂 In any case, the design is nearly identical to the “cMoy” amplifier design by Chu Moy, the founder of one of the first internet forums on headphones and headphones listening, headwize. The site is not active any more, but fortunately the excellent collection of headphone-related articles that was published there has been preserved – check it out!.

The recipe for this amp is my often-used “buy cheap ebay-kit and replace parts”, but this time I’ve probably gone a little more overboard than usual with my replacements (always nice to have lots of leftover parts in your collection ;)). The resistors are Vishay-Dale RN55 mil-spec, the electrolytics are Elna Cerafine and the input caps are Blackgate N bypassed with Mundorf M-Cap Supremes. The whole thing is powered by two 9V batteries in a Bulgin holder.

And the sound: Well, with the stock JRC4558 op-amp there’s only one word for it really – disappointing! Sharp, closed-in with very little sound stage and absolutely no way to ignore that you are wearing headphones. However, the beauty of the RA-1/cMoy design is that there is only one active part, so changing the sound by changing the op-amp is very easy. I had another look in the parts boxes and found a TI OPA2107 to try instead.

The glare and the edginess is now gone, the soundstage is wider (though there’s still no doubt you are wearing headphones) and the listening is much more enjoyable all round. I might try a few other replacement opamps as well (the AD8620 and the LM4562 would be good candidates I think) to see if it is possible to squeeze out a bit more performance. This isn’t a world-beating amplifier by any means, but with the right op-amp it is isn’t bad sounding at all.

The “Retro” balanced RIAA stage

Since I got my Pro-Ject turntable about two months ago I have been looking for a decent RIAA-design. I have an old Vincent, but it isn’t really good enough. Almost at the same time, I realized that Brian and Russ at Twisted Pear Audio were just finishing up a balanced RIAA design using differential opamps which they called the Retro. It looked like it might be worth a try, so I ordered some PCBs and the few parts that I were missing – sometimes it is nice to have a big cache of parts that can be used 😀

The build is dual-mono including power supply boards (the LCBPS also from Twisted Pear) and separate PCB-mounted transformers for each channel. It is a bit overkill with two transformers, but hey, they were just laying around anyway 😉 The observant reader will notice from the pictures that my ground wiring isn’t 100% correct – I am still trying to get my head around grounding in differential systems but for now it works fine with only a little hum in the speakers.

I haven’t spent two much time listening yet, but even with short tests it is obvious that this design is at least a few steps up from the Vincent, so although I have a few more RIAA-designs I would like to try as well, the Retro is definitely making the Pro-Ject (and the vinyl collection) sing 🙂

 

Desktop amplifier with the TDA8920 chip

Long weekend here, so I actually had time to finish a build – nice!. For the past couple of years I have been using a cheap ready-made amp based on the Tripath TA2020 chip for my computer. However, it was always a little lacking in power for the Piega speakers I use and a while ago it started cutting out in one channel, so obviously that’s the a perfect excuse to build a new one 😉 I spotted a kit on ebay based on the Philips/NXP TDA8920 class D chip that seemed to be worth trying out and so I did. The board integrates a speaker protection circuit based on the UPC1237 IC and also, very importantly, a startup delay that means I don’t get the “boing!” startup sound from the iMac out at full blast every time I turn it on (the amp is powered from a master/slave socket controlled by the Mac).

Once again, the build recipe is simple: Get a cheap ebay kit and replace the key components if they are not good enough and/or do not fit the application. In this case, that means I have kept the PCB, the IC and most of the other components, but replaced the potentiometer with a real Alps blue and the main capacitors with some that were shorter. I used a deep hifi2000 enclosure that fits better on the desk, but this also means I am not going to win any prizes for the wiring as the speaker wires are routed very close to (= on top of) the transformer. However, the amp is very quiet and there is not enough hum for it to be an issue, even when sitting very close to the speakers.

Sound-wise this is obviously not high-end, but for the application and price it is actually not bad at all. When properly implemented the TA2020 sounds better (at least to me), but if its 10 or so watts isn’t enough as in this case it does not really work, so overall this was a worthwhile upgrade.

/U.