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TI marches steadily down the road to oblivion

Posted 23rd October 2013 at 12:20 AM by abraxalito

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

http://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.
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Old

Prototype stereo balanced passive filter for Ozone

Posted 14th October 2013 at 06:57 AM by abraxalito
Updated 27th November 2013 at 01:42 AM by abraxalito

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...
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Old

Introducing the Ozone DAC platform

Posted 9th October 2013 at 11:51 AM by abraxalito

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...
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Old

TL431 output filter for TDA1543 current source elimination

Posted 6th September 2013 at 04:45 AM by abraxalito
Updated 6th September 2013 at 05:10 AM by abraxalito

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....
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Old

Tweaking the TDA1543 SDcard player

Posted 6th September 2013 at 12:05 AM by abraxalito

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...
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Old

My latest taobao toy....

Posted 2nd September 2013 at 02:55 AM by abraxalito
Updated 5th September 2013 at 06:51 AM by abraxalito

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...
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Passive fiilters - musings on inductors and topologies

Posted 5th August 2013 at 12:58 AM by abraxalito
Updated 5th August 2013 at 01:02 AM by abraxalito

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...
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Old

I2S transcoder

Posted 7th July 2013 at 12:57 PM by abraxalito
Updated 16th September 2013 at 01:32 AM by abraxalito (Schematics added, pic of 2nd build added)

Here's a circuit that's been a long time in gestation - some logic that converts I2S from 64fs (32bits per sample) down to 32fs (16bits).

Almost all the S/PDIF receiver chips nowadays output a bit clock at 64fs (2.8MHz for RBCD) because the format has the potential to support up to 24bits. When being driven from a CD player though, there's no chance of any useful information occupying those spare bits. As my interest is to run all signals as slow as possible to keep noise to the absolute minimum, 64fs to me is profligate generation of RF when 32fs will do the job. But only the WM8805 supports this format and then only when software programmed.

The other reason for wanting the slower bit clock is that my LAID design relies on shift registers and the 32fs clock gives me twice as good utilization of the serial storage - no bits are being wasted on zero padding.

This circuit is designed to do the job with the fewest standard logic chips I could manage...
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Old

Better sounding anti-imaging filter

Posted 5th June 2013 at 01:46 AM by abraxalito
Updated 5th June 2013 at 02:00 AM by abraxalito

Still in the vein of AIF designs which utilize off-the-shelf inductors, I'm currently listening to this one and its thoroughly enjoyable. I built it with some very cheap bobbin-wound (unscreened) 10mH chokes I found on Taobao.

I don't recommend using unscreened inductors for this but if that's all you have the results are still aural candy. They do pick up a little low level mains hum, not noticeable except when close to the speaker. Also they interact - when I was checking the prototype filter for continuity I hooked up the LCR meter to the 4 inductors in series and found different answers - none measured 40mH. The result was from 32mH to 45mH (from memory - my filters are balanced so I have four sets of series Ls). I have them spaced apart by almost one coil diameter (about 6mm) so if you're going to build this I suggest greater spacing.

You'll note that this one's industrial strength in terms of its stop-band rejection - around 60dB. Whether this is obtained...
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Old

Simple anti-imaging filter

Posted 28th May 2013 at 04:57 AM by abraxalito
Updated 4th June 2013 at 07:34 AM by abraxalito

If you're curious to see how an anti-imaging filter affects the SQ of your NOS DAC but have been hitherto put off by all the coil winding involved, then this circuit might be just the ticket.

I was curious to see how well just two inductors could do and it turns out not at all badly - there's about 23dB stop-band rejection here and the 10mH inductors are off-the-shelf Fastrons. The capacitors can be all 1nF 0805 C0Gs - just buy a strip of 40 and use parallel and one series combination.

I intended to build one and listen to how it fares against my more complex efforts...

Update - a quick listen and its clear on switching back to the original filter that this new filter's noise floor isn't as low. That's not directly perceived as a rise in hiss mind - this is the subconsciously perceived noise floor which translates to more attention given to the music. So I'll put the two inductor filter aside and work on slightly more complex filters next.
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