This one rocks - it plays FLAC, WAV and mp3s. The DAC is WM8740 (not so hot) but the designer has taken the power supply very seriously. Just check out all those caps and TDK noise filter on the PCB on the right Power comes from a lithium battery behind, so its portable but there's no case - there are acrylic front and rear panels screwed on to the PCB spacers. Two 3.5mm jacks provide headphone and line out.

Its using STM32F407 to do the decoding which is a first for ARM in this sphere and the design is configured that there's an I2S link between the two PCBs. So in theory anyone could design a better sounding DAC and replace that bottom PCB whilst keeping the UI. Which I may just do.... Price is 568rmb (just under $100).

Update - I was a little curious about the PSU so I've pulled out all of those SMT 220uF caps to get a closer look. The block filter's a Murata (not TDK) BNX024 which looks like a wrong choice of part primarily because its rated for 15A. Hence...

I'd like to be sure that my amp and the passive XOs in my speakers aren't significantly the bottleneck in the sound I'm getting from my DAC prototypes. To get a second reference point I'm starting to build a passive line-level crossover. Here's a pic of it taking shape - its using AD605s because I have plenty to hand and they're cheap and capable of being subjectively transparent with the right power arrangements. The pot core inductors are implementing LR4 XOs in balanced. Using the AD605s with their low input resistance and noise allows manageable inductor sizes for the XO - the largest being 9mH for a 3.5kHz crossover frequency.

Ah - I forgot to mention how I propose to do the transformation from normal (2V) line levels to the 70ohm impedance/20mV paradigm at the AD605 inputs. I shall be winding a pair of ferrite-cored step down transformers with centre-tapped secondaries Lots of turns to look forward to with 0.1mm or perhaps finer wire as I'd like to get at least 5H...

A few weeks ago I built an almost completely passive analog output stage for my DAC/filter front-end and found it sounded noticeably quieter than my active ones which have been using AD605 and AD8129. The only active component in the experimental stage was a single emitter follower buffer run in classA - voltage amplification was achieved by a much higher than usual I/V resistor and passive filter specially designed for the higher impedance.

The comparison left me rather puzzled as to what was clouding the active stages. It turns out it was inadequate power supply decoupling - the fix is an abundance of ceramic capacitors soldered across the top of the chip.

On the AD605, the feedback resistor in low gain mode is a relatively low 820ohms which presents something of a challenge. Also I'm using an inverting stage following with a similar value input resistor. While the low combined values don"t present any significant challenge to the output stage itself (which...

But hey, its stock is 30% up on the year!

https://www.testosteronepit.com/home/...verpriced.html

Wolf is a little bit too polite in his analysis of TI's woes - #1 is crappy strategic thinking.

Here's my first stab at an affordable yet screened passive filter using off-the-shelf inductors. Its a 17th order quasi-Chebyshev using 8 equal valued series L and 9 shunt caps achieving slightly better than 50dB rejection at 24.1kHz.

Update - this might be the first and last filter I build with these Coilcraft inductors. (If anyone's interested, the part no. is LPS6235-335). Reason being - on trying to order more, the price got hiked more than 100%. Originally these were attractive because on Taobao there was a source selling well below the manufacturer's list, but that seems to have dried up. At the list price in USD, there are other alternatives potentially better value. However none with the same inductance (3.3mH). The key feature is the Q - the Coilcrafts have a Q around 40 at 20kHz - this is very hard to beat in such a small package. As a reference, my pot-core hand-wound inductors have a Q about 160 but they're huge in comparison, so these tiny inductors are actually...

The time has come to talk about the overall aim of my DAC developments - a modular DAC platform for DIYers and audio systems integrators. By this word 'platform' I mean this isn't going to be presented as a single end-to-end design that you can order up from a friendly reseller. Nor is this an 'open source' design, although it is open to anyone to use or adapt with no restrictions. Rather this is a DIYer's DAC architecture a series of interconnected modules that are subsystems from which an audiophile grade DAC can be assembled.

When I say 'audiophile grade' what I mean is this is a design optimized for aural satisfaction, not for the numbers. To be even more specific, its been optimized to give the highest perceived dynamics (within the limitations of the chosen DAC chip) rather than the lowest THD+N and flattest FR. If you're looking for ODAC-type measurements, feel free to move along now That's not to say measurements have been ignored, rather they're very much in the...

Here's what I've ended up with in my SDcard DAC for eliminating the pull-up current sources within the TDA1543 - a heavily filtered 3.75V reference. For a single TDA1543 just connect the L and R 870R resistors to the output of this filter instead of the normal connection to 0V. Then the input's fed with the TL431 - I'm using 3k and 1k5 output voltage setting resistors. The first resistor and inductor on the left are my attempt to simulate the output impedance of the 431.

The electrolytics are Sancon 16V types with 0.1R ESR - the 440uF being made of two in parallel. The inductors need to have the right ESR (about 0,1ohm also) for which I had to wind my own 68uH - the ready made ones I have are too lossy Varying these parameters might result in a lumpy frequency response.

Attenuation is -70dB by 20kHz but almost flat to 1.6kHz and output impedance remains low down to DC.

Eliminating the current sources means that pin7 of TDA1543 now goes unconnected....

This board is really a fun one to tweak mainly because its so simple and relatively self-contained, so results of mods can be verified very quickly.

In stock form, the sound is fairly typical 1543, nothing unpleasant but an almost total lack of soundstage depth. On recordings with a high ratio of ambient to direct sounds (Nimbus) the acoustic cues are muddied. The flatness of presentation is one of the reasons I was so slow to accept 1543's other virtues during the course of development of my DACs. Soundstage depth is a biggie for me. There's also a lack of 'finesse' on the HF - lack of 'poise' or 'delicacy'.

I started by fixing up the grounding to enforce a star earth on the analog outputs and power supply. Then went on to filter the DAC's supply regulator (7805) with series ferrite beads and additional lytics and ceramics. It later transpired that the beads were being shorted by a parallel track on the other side of the board. I installed filtering prior to...

Its a TDA1543 SDcard player. Not hooked up yet to my amp but looks to be a really simple and quick way to get analog-like digital sound on the cheap.... The digital part is a dsPIC, it would have been better if it were an ARM (much lower power) but this looks to be a good start. Can't argue with a price of 150rmb, considerably cheaper than the QA550 and it does have an I2S output connector For those who prefer to do their own DAC, the vendor also looked to be selling the pre-programmed dsPIC for 40rmb.

Update - I tried powering this up and no sound . There's most likely a problem with the format or type of SDcard I'm using. There's no I2S signal being sent to the DAC which suggests the dsPIC hasn't recognised what's on the card. But there is activity on the card pins so its definitely attempting to read it.

Update 2 - had a chat on QQ with the designer/seller and he mentioned that the .wav files must be placed into directories and I was trying with just a...

I've spent many hours recently poring over webpages and catalogues of inductors, looking for the best bang-for-the-buck in relation to anti-imaging filter inductors.

The gold standard, where performance is uppermost and cost and size are subsidiary, looks to be still the gapped ferrite pot cores I started out using. Their disadvantages are they need to be custom wound, not being available off-the-shelf, and their consequent higher cost. They also produce relatively bulky filters when a dozen or more are called for in a design. I've found nothing to beat them in performance, particularly accuracy and repeatability of their value and in terms of achievable Q (I've seen 500-plus in some cases on my meter).

I do hanker after a more portable and easier to replicate design though hence my investigations into cheaper alternatives.

Right down the bottom of the pile are the bobbin-wound coils, available in a wide variety of values here, at stunningly affordable...