diyAudio - abraxalito
Go Back   Home > Forums > Blogs

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Old

Analog stage for Ozone DAC

Posted 28th November 2013 at 10:55 PM by abraxalito
Updated 12th December 2013 at 06:53 AM by abraxalito

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...
abraxalito's Avatar
diyAudio Member
Views 512 Comments 6 abraxalito is offline
Old

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.
abraxalito's Avatar
diyAudio Member
Views 313 Comments 0 abraxalito is offline
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...
Attached Thumbnails
Click image for larger version

Name:	stereo_TL-filt.png
Views:	233
Size:	532.5 KB
ID:	1155   Click image for larger version

Name:	P4270069.JPG
Views:	142
Size:	77.9 KB
ID:	1157   Click image for larger version

Name:	third-gen-filt.JPG
Views:	172
Size:	79.5 KB
ID:	1169   Click image for larger version

Name:	P5220072.JPG
Views:	93
Size:	76.4 KB
ID:	1172  
abraxalito's Avatar
diyAudio Member
Views 827 Comments 17 abraxalito is offline
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...
abraxalito's Avatar
diyAudio Member
Views 824 Comments 8 abraxalito is offline
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....
Attached Thumbnails
Click image for larger version

Name:	TL431-output-filter.png
Views:	498
Size:	7.4 KB
ID:	1122  
abraxalito's Avatar
diyAudio Member
Views 840 Comments 3 abraxalito is offline
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...
abraxalito's Avatar
diyAudio Member
Views 528 Comments 5 abraxalito is offline
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...
Attached Thumbnails
Click image for larger version

Name:	TDA1543_SDCARD.jpg
Views:	436
Size:	551.1 KB
ID:	1121  
abraxalito's Avatar
diyAudio Member
Views 637 Comments 0 abraxalito is offline
Old

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...
abraxalito's Avatar
diyAudio Member
Views 483 Comments 0 abraxalito is offline
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...
Attached Thumbnails
Click image for larger version

Name:	I2Slogic1.JPG
Views:	513
Size:	69.0 KB
ID:	1110   Click image for larger version

Name:	I2Slogic2.JPG
Views:	317
Size:	63.1 KB
ID:	1111   Click image for larger version

Name:	P3110065.JPG
Views:	256
Size:	673.7 KB
ID:	1134  
abraxalito's Avatar
diyAudio Member
Views 1568 Comments 28 abraxalito is offline
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...
Attached Thumbnails
Click image for larger version

Name:	4inductor-AIF.png
Views:	374
Size:	12.7 KB
ID:	1091   Click image for larger version

Name:	4inductorAIF-plot.png
Views:	200
Size:	3.6 KB
ID:	1092  
abraxalito's Avatar
diyAudio Member
Views 565 Comments 0 abraxalito is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 10:59 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2