Go Back   Home > Forums > Blogs > abraxalito

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
DAC design and development Digital delights - getting the most from your DAC chips.
Old

Ozone Chebyshev filter

Posted Today at 02:39 AM by abraxalito

I've munged the earlier 8 inductor filters down to only 5 - this one is using off-the-shelf TDK inductors, SLF7045-681, albeit they need to be hand-selected to get the correct values as the production tolerance is 20%. X7R caps sound just fine, surprisingly

FR is -3dB at 17,8kHz with around 0.25dB of passband ripple.
Attached Thumbnails
Click image for larger version

Name:	Ozone 5th filter.png
Views:	1
Size:	9.6 KB
ID:	1270  
abraxalito's Avatar
diyAudio Member
Views 7 Comments 0 abraxalito is offline
Old

Hexacap-based Ozone DAC

Posted 20th March 2014 at 03:18 AM by abraxalito
Updated 31st March 2014 at 01:07 AM by abraxalito

Here's my current bench lash-up DAC based on three hexacaps. Total capacitance of the order of 1.3F.

32fs EIAJ is fed in, balanced, from the left, the central hexacap feeds two TDA1545ATs. Filters are TDK inductor based, six stage balanced with X7R caps (gasp!). Caps in the centre provide the mid-rail power (2.5V) which the I/V resistors are fed from. The two hexacaps on the right power the post amps based on AD815ARBs, gain set roughly to 26dB with a little NOS droop correction. They're the postage-stamp sized boards roughly in the middle. Output is differential and fed to ferrite-cored transformers to convert to SE.

I'm blown away by the dynamics of this, given the right recording. Next up is an amp based on paralleling 8 or 10 AD815s. Each fed from its own hexacap, of course....

Update1 - the DAC supply has now been upgraded to two tiers of the 4700uFs, interconnected by six 1.5mm diameter solid copper wires. Capacitive reactance measures 2.5mohm...
Attached Thumbnails
Click image for larger version

Name:	P1010092.JPG
Views:	131
Size:	713.7 KB
ID:	1260  
abraxalito's Avatar
diyAudio Member
Views 289 Comments 16 abraxalito is offline
Old

Adventures in low impedance power supplies

Posted 10th March 2014 at 08:01 AM by abraxalito
Updated 2nd April 2014 at 10:29 AM by abraxalito

Here's my latest crazy project, intended to answer the question 'How low can you go?' in power supply impedance. No listening tests yet, I've just finished assembling this stack of hexagon capacitor arrays out of cheap electrolytics. Total capacitance of the top 4 tiers is comfortably above 1F. The top tier is designed for lowest ESR at HF using Nichicon 1500uFs, the next tier is a trade between ESR and uF. The last two are the highest capacitance density I could find (a total of 182 4700uFs). I've yet to connect the bottom two hexagons to the upper tiers but the top two are connected by wires running through the gaps between caps.

The whole is intended to push the limits of low frequency noise in powering a couple of TDA1545s which will sit on a small PCB supported on thick wires from the centre of the top tier. I am aiming to get a capacitive reactance (at 50Hz) at the DAC supply pins below 3mohm and ESR below 1.5mohm.

Update1 : connected the bottom two tiers...
Attached Thumbnails
Click image for larger version

Name:	wedding-cake.JPG
Views:	133
Size:	691.1 KB
ID:	1253   Click image for larger version

Name:	OST4700uF.jpg
Views:	47
Size:	171.7 KB
ID:	1254   Click image for larger version

Name:	5captier.JPG
Views:	68
Size:	673.4 KB
ID:	1255  
abraxalito's Avatar
diyAudio Member
Views 298 Comments 4 abraxalito is offline
Old

Next generation Ozone analog stage - 'free radical'

Posted 25th January 2014 at 01:28 AM by abraxalito
Updated 6th February 2014 at 03:49 AM by abraxalito

Last night I finished building the second channel of my dual mono approach to DAC building which I've called 'free radical'. Here's a picture of the second channel's build just prior to adding all the crapacitors (cheap shanzai 'Sanyos' which measure extremely well). While building the second channel I was listening to the first in mono and that was a spur to quick completion

From left to right there's the AD605 with its top hat array of MLCCs - outputs are isolated via ferrite bead chokes from the AD8017 under its own pile of SMT ceramics. In between the two active stages are the capacitors associated with power supply reference voltage filtering. I realized from the previous build that as the AD605's gain is controlled by DC voltages, these voltages need to be low noise to ensure gain stability. Hence lots of RC filtering with those Nichicon and Rubycon low ESR lytics. I'm using BC817 transistors as low drop-out regulators and the reference voltages (2.5 and 5.7V) come...
Attached Thumbnails
Click image for larger version

Name:	free radical.JPG
Views:	128
Size:	672.2 KB
ID:	1229  
abraxalito's Avatar
diyAudio Member
Views 433 Comments 7 abraxalito is offline
Old

Ozone beta-build listening

Posted 8th January 2014 at 05:18 AM by abraxalito
Updated 8th January 2014 at 06:15 AM by abraxalito

I've had the beta build Ozone (no input stage yet, fed from my QA550 via the I2S transcoder to down-convert to 32fs) playing out 24/7 for a few days now.

Overall I'm very happy with how it sounds, just a minor gripe about sibilance on some operatic vocals which I'd like to understand better. On the upside the jump-factor (read dynamics) and soundstage stability (holographic on the right disks) are about the best yet. I'm using a couple of Decca double CDs for this - 'La Traviata' and "La Boheme'. They're about the most transparent sounding and demanding disks I have. Demanding in the sense that they have lots of emotional drama which should positively engage my attention if the DAC's really up to snuff. I never much enjoyed opera until I got into building my own NOS DACs, but now I really enjoy my dramatic fixes and these two recordings are really top of the pile. They're about 50 years old but so far I've not found anything newer which touches them (not that I've looked...
Attached Thumbnails
Click image for larger version

Name:	P1010081.JPG
Views:	111
Size:	261.7 KB
ID:	1208   Click image for larger version

Name:	AD605-internal.png
Views:	135
Size:	47.8 KB
ID:	1209  
abraxalito's Avatar
diyAudio Member
Views 325 Comments 6 abraxalito is offline
Old

Ultimate SQ DAC

Posted 27th December 2013 at 06:08 AM by abraxalito
Updated 30th December 2013 at 12:52 AM by abraxalito

Inspired by this thread http://www.diyaudio.com/forums/digit...-new-post.html
I've been giving a little thought for how to move beyond the 'Ozone' to a DAC able to handle more than 16bit inputs and up to 96kHz input rate. The target being 20bits and 120dB SNR (non-A weighted). The OP in that thread preferred a more marketable 'ultimate' DAC (with 192k and potentially 384k capability, along with DSD) - aims which to my way of seeing clearly conflict with a DAC having any pretentions to ultimacy.

The simplest solution - building on the digital part I already have - would be to add more TDA1545As in parallel and with a Cortex M4 direct the data to the respective chips. What's unclear though is how low the noise will go when the extra chips are added. From the DS, an A-weighted SNR is quoted of 101dB (typ) with 2mA, however this is a static noise (code = 0) and hence may well not translate to the noise achieved with bits toggling....
abraxalito's Avatar
diyAudio Member
Views 451 Comments 2 abraxalito is offline
Old

The coolest Taobao SD card player yet

Posted 10th December 2013 at 03:50 AM by abraxalito
Updated 21st December 2013 at 12:48 PM by abraxalito

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...
Attached Thumbnails
Click image for larger version

Name:	P6050075.JPG
Views:	206
Size:	66.8 KB
ID:	1176   Click image for larger version

Name:	P6050076.JPG
Views:	204
Size:	79.9 KB
ID:	1177   Click image for larger version

Name:	P1010080.JPG
Views:	116
Size:	79.2 KB
ID:	1193  
abraxalito's Avatar
diyAudio Member
Views 592 Comments 17 abraxalito is offline
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 379 Comments 6 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:	189
Size:	532.5 KB
ID:	1155   Click image for larger version

Name:	P4270069.JPG
Views:	117
Size:	77.9 KB
ID:	1157   Click image for larger version

Name:	third-gen-filt.JPG
Views:	119
Size:	79.5 KB
ID:	1169   Click image for larger version

Name:	P5220072.JPG
Views:	68
Size:	76.4 KB
ID:	1172  
abraxalito's Avatar
diyAudio Member
Views 643 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 618 Comments 8 abraxalito is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 09:10 AM.


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