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Ozone Chebyshev filter

Posted 18th April 2014 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 :D

FR is -3dB at 17,8kHz with around 0.25dB of passband ripple.
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One Farad capacitor array

Posted 3rd April 2014 at 03:08 AM by abraxalito
Updated 15th April 2014 at 06:28 AM by abraxalito

This array of 127 10,000uF caps measures -j2.9mohms at 50Hz which I reckon makes it comfortably over 1F in capacitance. ESR is 1mohm @ 50Hz.

The individual caps were measuring on average 8,500uF. Although they're marked 10V (the brand is ChengX a slightly shady Chinese one) they're not good for anywhere near this voltage. I reckon they're in reality 6.3V and they seem to have decently low leakage at this working voltage. I shall be using them at 5V or below.

Update1 - seems I wasn't using enough copper in the wiring. I've now built a second one with 2.5mm2 wiring around the loops and 1.5mm diameter cross links and ESR is down to 0.5mohm @ 50Hz now, decreasing at higher freqs. I have enough caps left for a third one...

Update2 - now the first array has a basement level giving 2.1F total with ESR below 0.4mohms @ 50Hz. There are six paralleled TDA1387s atop the combined hexagons giving unprecedented LF dynamics. Amp long, long overdue for an upgrade...
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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.... :p

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...
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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...
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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 :D

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...
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Triton One speaker unveiled at CES

Posted 17th January 2014 at 02:45 AM by abraxalito
Updated 17th January 2014 at 02:57 AM by abraxalito

Just for a change from DACs, here's a speaker which caught my eye.

[URL]http://www.avsforum.com/t/1511825/goldenear-triton-one-at-ces-2014[/URL]

Now how much of its improved SQ over rivals three or more times the price is going to be down to the active bass section offloading the most PSU-draining signals from the driving poweramp? The comments about the scale of the soundstage do reflect the kinds of improvements I've been getting by reducing LF noise in my DAC, so the reduced LF noise from the poweramp from having a more benign load to drive could indeed be key. 92dB efficiency certainly helps a lot in reducing poweramp PSU stress.

That article says this speaker is 'sure to shake up the industry'. [I]Really[/I]? What do you guys think?
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Stereophile's measurements of dCS Vivaldi DAC

Posted 9th January 2014 at 02:59 PM by abraxalito

John Atkinson's 'WOW!' (more than once) to his measurement results from the Vivaldi DAC prompted me to have a closer look at how it does for noise modulation.

The AP's FFTs shown don't come with details about the number of points in the FFTs, so noise estimates are a tiny bit tricky. However there is enough detail to make some reasonable estimates.

I've attached the plot from which I'm making my estimates - if anyone notices I've made a slip-up, please do comment and correct me.

The red line shows white noise at peak level of -4dBfs. I generated white noise in Audacity at this level to compare - with the maximum 16k point FFT and BH windowing, I got the same level of noise as on this plot - -42dBfs in 22kHz bandwidth. That suggests to me that the FFT shown has 64k points.

Another way to estimate the noise is by looking at the difference between the blue plot (19.1kHz, 0dBfs) grass and the red. To my eye, the difference in level is 76dBr...
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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...
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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 [URL]http://www.diyaudio.com/forums/digital-line-level/247700-ultimate-multi-channel-dac-new-post.html[/URL]
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...
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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 :D 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...
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