Swiss army DAC?

A while ago I showed a Bluetooth DAC board I bought from Aliexpress. While I work out exactly how to implement that board, here is its “predecessor” in finished form.

The basic concept is the same, a QCC5125 Bluetooth module and a separate DAC chip – here an ES9018Q2M – on a small board, along with the required PSU components. Combined, this means you get both Bluetooth connectivity and a separate analog input (switched with a real relay no less) that will operate from a single supply between app. 5-25VDC – and even from an AC supply as well.

To get volume control and a bit more drive capability as a “real” preamp I’ve teamed it with the single-supply version of my “MiniPre” board and a 24V filtered IRM module as the power supply. The original plan was to power both boards from the same supply but that didn’t work. After a fair bit of head-scratching I worked out that it caused grounding issues and I very nearly abandoned the whole project idea altogether. The solution ended up being adding an isolated DC-DC converter to step the voltage to the DAC down to 12V and isolate it. This works well, but if it looks like an afterthought that’s because it is 🙂

This little device may not be that last word in quality, but it still makes quite a nifty little front-end for desktop or testing use as far as I am concerned, so looking forward to getting it hooked up in its new home on my lab desk 🙂

Jack of all trades…

Another Aliexpress purchase, which basically started with a simple plan to create a “test source” for my desk. Whenever I want to test a new build, I seem to be running around the whole house looking for a phone or iPod plus any number of cables to get everything connected up, so having something that lives on the desk should be a big time-saver.

I have bought one of these wireless DAC-boards before, but decided to check what the market offers now. There are quite a lot of different variations to pick from, but in the end I decided to choose one of the “high-end” options because the price difference isn’t huge.

On the face of it it, this is a wireless DAC based on a QCC5125 bluetooth chip and a ES9038Q2M DAC, however look closer at the board and the list of features gets substantially longer:

• AC or DC power supply with a pretty wide range.
• Analog input with a submini relay for switching.
• Connection for external antenna.
• Upgradeable (socketed) opamps in the analog section (stock ICs are JRC4580s).
• Switchable additional digital inputs (I2S and Coax).
• IR control with pins for an IR receiver.
• PC control via pins on the board.

There is not much information on how to make all of this stuff work, but let’s start with a few small experiments and see what we can manage to work out before crying for help 🙂

I also noted that the board has its own I2S master clock signal (MCLK), so a Raspberry Pi (Zero) should actually make this complete “all-in-one” front-end solution with built-in streaming etc. Not what I originally envisaged, but maybe it can be incorporated anyway. Like the title alludes to, this little board may not be the last word in quality, but to me versatility has a charm of it’s own 🙂

Last of a dying breed?

Yes, this is a DAC and no, those are not a dying breed as such. However, it is an AKM-based DAC, and since the main AKM factory burned down last year, those have been dying out as the supply of ICs dried up. I believe AKM is planning to restart production of at least some of their ICs but I am not sure when, and the reality is that DAC design is pretty complicated and so they may not be able to win back the customers that they have lost when they do eventually restart production.

I was reminded of this by a recent blogpost from Jason Stoddard of Schiit Audio that deals with exactly this problem as Schiit was one of the AKM customers and they have had to convert their products to ESS DACs instead. As I think I have mentioned in the past I have tried several ESS-based DACs and somehow always found them impressive at first, but tiring in the long run. Not sure why but that’s just how it is and so I am obviously not enthused by an outlook of nothing but ESS-based DACs in the future. The DAC chip at the heart of my board is the AK4497, so not quite top-of-the-range but still a part that is/was used in several very expensive commercial products.

The background for this build (which I completed a few weeks ago) is simply that I came across this unwanted kit on diyaudio.com a few months ago. The price was pretty good and since it was (almost) complete but still an unassembled kit, I had the opportunity to add my own touches to it – which is exactly how I prefer it. It’s also got a few details I like, such as the onboard connectors and the muting relay on the output, so for the price I paid I thought it was a bargain.

No concrete plans for the board just yet, but having a DAC with all inputs available is very nice as a kind of “future-proofing” for a digital signal chain. The board even takes a separate USB-module which I don’t need right now, but still plan to add for the sake of completeness.

More finished stuff!

Although there is a tiny bit of light at the end of the Covid-19 lockdown-tunnel (at least in my part of the world), the “new normal” (or at least “interim-normal”) of working from home and attending lots of online meetings still continues. This means I also continue to have more time than usual for building, so I’ve managed to complete a few more projects over the last week or so. I know it might not seem that much, but compared to my usual rate of progress it’s starting to feel like an assembly line! 🙂

First up is the AD1865-based DAC I showed here. It works as intended and sounds fine, but honestly I need to redo the wiring because it’s not really optimal. Not now though 🙂

Next is my 50ASXBTL-based amp. This is the original “prototype” I did of the SE-BTL conversion for the ICEpower 50ASX modules and while there have been some reports on diyaudio that the conversion isn’t as straightforward as I made it seem, I can confirm that at least based on sound the finished product still works well.
However, the last strech of this build wasn’t without issues, firstly because I had to redo the bottom plate as I realised that glass fuses on the primary side of an SMPS is not only a bit stupid, but also not necessary when each PSU is already fused on the board. Secondly, that turned out to be the easy part because I did most of the wiring by memory which in hindsight wasn’t the best choice. Anyway, after a few more attempts than I expected (and after swearing at everyone and everything including my own stupidity) it actually works well now – nice!

Last, but definitely not least, is the basic ICEpower700AS2-based power amp I showed here. This deserves a new 10mm custom front panel at some point, but it plays well and for now I think getting some more listening impressions is higher on the agenda. My initial impression is that this could well be my all-time favourite ICEpower-amp, but let’s see how it goes when I put a few more hours on it.

Hopefully this week will bring a new batch of front panels (or actually, rear panels) so I expect to be able to keep up the current level of progress a little while longer 🙂

Back to the future – of DACs?

For pretty much as long as I can remember, there has been a DAC “arms race” going on where manufacturers competed to give the biggest numbers – 16, 18, 20, 24, 32 bit resolution and 48, 96, 192, 384, 768 kHz sampling rates. Irrespective of whether you had the source material to make use of these massive numbers – or even whether the laws of physics made them obviously pointless in the real world, the “bigger number is better” philosophy was still adhered to.

For a few years though, some people have been going “back to basics” with DAC chips such as the TDA154x and others, as wells as discrete “R2R” dac designs such as the Soekris boards and the Schiit Multibit converters. These designs often don’t offer the full resolution of high-res material, but if you don’t care about that – or if you are still listening primarily to 16/44.1 material – then they offer something else, namely a different (many would say “better”) sound. I’ve previously written that I find the ESS ES90xx dacs to often be very impressive at first, but after a while I get a bit of listening fatigue. It could be me or my imagination, but it’s happened enough times that I start to see a pattern (at least when system matching doesn’t mask it) and so I have been trying to stay clear of ESS-dacs and see what else is on the market.

Now, as usual for this I don’t really need another DAC, but I am still curious 🙂 Not quite curious enough to splash out on a Soekris board to play with to be honest, but still curious enough to clicking the “buy it now” button on ebay for this board. It’s based on the AD1865 IC in dual-mono configuration and once again what pushed me over the edge was that I could get a half-finished board with SMD components soldered, so I had some influence over the design of the board.

Assembly was quite easy because I only had to pick and mount the through-hole parts, but even that was enough to make me remember how much I hate black PCBs. Not only because the seller showed that the board was green in the picture, but also because this is a matte black finish that I haven’t seen before and which makes it 99% impossible to see any traces on the board. Fortunately everything worked the first time, but if it hadn’t I am not sure I would have bothered with that much troubleshooting before giving up. Manufacturers: I know green PCBs are considered “boring”, but they WORK! or if you desperately want something else then blue or red still allows you to see the traces, so please stick to those colours. (OK, rant over 🙂 )

The board has one coax input. I opted for a BNC here because that was the socket I had on hand and that might end up being a mistake, but it works now (with an adapter). There’s also an I2S input meaning it’s possible to connect a second source such as a USB card or similar. As usual, I’ve only done basic listening testing with “baseline” I/V opamps (the OPA2134 and the LME49710) but it’s definitely not making a bad first impression 😀

Not quite sure what to do with this one yet, but possibly a “Music box” version 2? Anyway, more listening impressions to be added later I guess.

Desktop DAC with a cheap ES9038-board…

Last year I mentioned that I had bought a cheap ES9038 DAC-board and now that’s starting to come together. This will be used as a controller to feed a pair of active monitors on my desk (that’s the “need” I mentioned in the original post) where it will save me a box as I currently have a separate USB DAC and passive pre). To make the box a bit more versatile (and to use some of that empty space inside…) I am thinking about including a Raspberry Pi Zero W in the box and connecting it to the I2S-input of the DAC plus add a potentiometer for volume control (digital on the DAC via an onboard uC). The ES9038Q2M DAC is asynchronous with its own clock so perfect for use with the RPi and this combination would give a Volumio-based source with two additional digital inputs and a volume control. That means that can be connected directly to a power amplifier input or active speakers – perfect for the desktop or a second system!.

The slightly unusual power arrangement with 5V input to a DC-DC converter is to support this setup. It will allow the RPi to be powered on constantly while the DAC power can then be switched on and off. I bought an early (”first generation”) of the ES9038 board with a slightly different power setup than the current version and crucially no DC input connector that I did not need (of course the newer versions of the DAC board can be used as well). Check the diyaudio-thread for the board for loads more examples of how people have been hacking this by the way – some of them are close to unrecognisable.

The original idea was basically to allow the power source to be a cheap 2A USB-charger, but reality seems to have thrown a spanner in the works here – none of the chargers I have tried will actually let the DC-converter start properly because of the high inrush-current it draws. Using a slightly more beefy 5V supply fixes the problem though, so the concept is more or less intact anyway 😀

Part of what drew me to this DAC-board originally were the on-board connectors, but as I couldn’t find any mechanical drawings having to make the back panel by hand seemed a bit of a risk. Using my own measurements and the datasheets of the connectors I managed to trace it out and with judicious use of paper printouts from Frontpanel Express to check the dimensions against the physical board it actually fits well for a first time attempts – although this is definitely an occasion where I would wish for a 3D-printer or a laser cutter to make prototypes before betting my money on ordering “the real thing” from Schaeffer/FPX (they are becoming quite expensive I think).

Soundwise this seems quite close to the other ESS-based DACs that I have tried. I am not sure that is such a good thing to be honest, but I am prepared to compromise a little bit on my desk where convenience is important and the differences aren’t night and day anyway 🙂

Small thing – big difference

I don’t normally write (much) about the commercial gear that I buy, but for once I’ll make an exception.

I’ve actually owned both the previous versions of the Audioquest Dragonfly (DF) USB DACs but sold them after a relatively short time because I did not really need them anyway. Thanks to an ad on a local classifieds page I now find myself as the owner of the third generation DF as well – the Dragonfly Red. Apart from the new looks – which I really like – the new series of DFs also have the benefit of much lower power consumption, meaning they can be used with mobile devices.

I therefore tried hooking up the DF to both my iPhone and iPad. To be honest I wasn’t expecting that much, but it really does make a significant difference to the sound quality. The downside is of course that your phone becomes quite a bit less portable with a couple of extra dongles and adapters hanging off it, but the benefit in sound quality seems worth it. I wouldn’t use it every day, but if I really had to travel light then using the DF would save me packing and carrying a separate music player which could be very handy.

Photo of the device and a “real” red Dragonfly as well for comparison 😉 (that picture was taken by yours truly in Hong Kong – coincidentally exactly two years ago today)

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 🙂

Work in progress….

It’s been a while since I have posted here, but real life is still getting in the way of my build time. At the moment this means I am mostly starting up new projects, because for some strange reason I can always find time to start new projects – even when time to finish the old ones is nowhere in sight 😀

I have been shopping a little at diyinhk.com recently and bought several DAC boards and power supplies, so one a few DACs are in the cards for sure 🙂 Also, one or two gainclones might make an appearance as well at some point. One reason for this is that I rediscovered some pictures of the Audiosector “Patek” amp a couple of weeks ago, so guess who has been scouring ebay etc. for reasonably-priced copper bars lately? 😉

Lastly, the Borbely and the Le Monstre front/rear panels have arrived and I am pretty happy with those, so now I am just waiting for my transformer order and a free weekend and then at least that should be sorted out.

However, I have to say that even with not much new going on there are still plenty of people that find their way here. The blog was at 15k page views in the beginning of January and it is now over 21k views total – I can’t complain about that, so thanks a lot for stopping by 😀