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abraxalito abraxalito is offline

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About Me

  • About abraxalito
    Biography
    Ex professional- and consumer audio designer. Prior to working in audio I was in embedded systems.
    Location
    Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
    Interests
    Maximizing dynamics and soundstage depth for the least money with multibit DACs
    Occupation
    English teacher, disruptive innovator with ARM Cortex M-series
    Country
    United Kingdom
  • Signature
    "Having people devoted to attacking you even in unfair, invalid or personal ways is actually valuable for keeping one honest and self-reflective." - Glenn Greenwald

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  • Last Activity: Today 07:18 AM
  • Join Date: 19th September 2007

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Latest Blog Entry

Posted 16th February 2015 at 12:50 AM by abraxalito Comments 9
Posted in Uncategorized
Here's something very misleading in the 6moons preview of Vinni Rossi's (of Red Wine Audio fame) latest supercapacitor powered kit. They have 18 * 350F supercaps in the box and they say '...the total rating becomes a whopping 6300F'. However each capacitor is only 2.7V so presumably to get any audio signal at all out, they need to operate these caps in series. Caps in series don't multiply, they divide so the total capacitance drops by a factor of 18. Hence only 19.4F. Not a small difference from 6300F or did I miss something?

http://www.6moons.com/audioreviews2/vinnierossi/3.html

I think I may have missed something - they aren't using all the supercaps all the time, rather there are 9 discharging and 9 charging. So the total capacitance in the audio circuit at any time is 350/9 = 39F. Still an impressive amount of capacitance but the problem is that the ESRs add too. Here's the datasheet for the Maxwell 350F ultracap they appear to be using - http://www.tecategroup.com/capacitor.../BC_series.pdf...

Posted 16th January 2015 at 12:55 AM by abraxalito Comments 10
Thanks to Matthieu (Malefoda) for the heads up on this. It looks distinctly like a DAC inspired by the DAC-AH - note not only the 8 DAC chips but also the PCB layout closely follows that design's. The price on Taobao is about half the AH (368rmb) so I shall be ordering up one or more to have a play. Matthieu found it on another website with prices in USD, here - http://www.cart100.com/Product/42124644877/.
Note there are two options here (blue, black) - the cheaper one is a kit of parts I believe, the more expensive ($84) the finished unit. Going on the translation of the Taobao page, the kit does not include the transformers, mains switch or the case.

Update : here's the summary of the mods so far, for details go to Malefoda's thread linked in the comments.

1) Re-route the output ground so the opamp filtering caps aren't subject to injected CM noise from the destination component (amp or pre).

2) Reduce the supply voltage to the output opamps...

Posted 12th January 2015 at 02:57 AM by abraxalito Comments 8
Last night the battery of my I2S source ran out so while it was on charge, I unboxed my last remaining Lite DAC-AH to have a listen to that, fed from my (mains powered) QA550 wav player. I'd bought 3 DAC-AHs a few years back when I was playing with them.

The differences between the stock DAC-AH and the Ozone Pagoda were apparent in the areas of soundstage depth, dynamics (especially at LF) and coarseness at higher levels. So this got me wondering what would be the lowest hanging fruit in terms of mods to it. My procedure before had been to implement everything I could think of before having a listen - this way its not possible to know which mods are the most effective ones and which can be omitted.

This time I'm going to be a bit more disciplined for the purposes of discovering which mods deliver the best bang for the buck. The first one I'm going to try is a passive LC filter between the DACs and the AD847s. Here's the schematic for it - its using the cheap and...

Posted 31st December 2014 at 08:36 AM by abraxalito Comments 4
Here's the 'Ozone desktop pagoda' DAC for 2015.

A single TDA1387 feeds a 3 inductor quasi-elliptic filter followed by AD8017s as buffer-amps. The large ferrite cores in the base do the bal-SE conversion. The power supply is 4 * AA NiMH cells which should in theory last for a whole day's music.

The design is really a 'MkII' version of the Ozone portable where the AD815 buffers have been replaced to allow a more compact construction and lower power draw without the constraint of being able to drive IEMs directly. Whereas the portable used a stack of 1387s due to the choice of 7mm TDK inductors, this one's using pot-core chokes giving a much higher working impedance and hence higher output levels from just the one DAC chip. The desktop footprint is about that of a CD.

Update : I found some bargain Jamicon caps on Taobao which give the tower more elegant proportions, as well as improving the supply impedance to the buffer-amps and giving more breathing...

Posted 15th November 2014 at 03:51 AM by abraxalito Comments 4
I'll outline here some thinking in choosing the major building blocks (aka ICs) for this card - any comments welcome as this progresses.

First up the DAC chip will be the TDA1387 initially. I don't know for sure that the output from the ARM/Xilinx card is I2S but I'm going to verify that fairly soon. There's nowhere near enough room for the passive shunt I've adopted previously so the bass performance probably is going to have to suffer. I shall pay considerable attention to the power supply arrangements though in an attempt to make up for the LF lack.

After the DAC, passive I/V will follow and then a filter using the TDK 7mm inductors I've used previously. I've slotted them into the gap between the PCB and the case and there's just enough height available. Since space is at a premium I'll experiment with a 3 inductor design - the stop band attenuation will suffer but probably I'll add a secondary LC filter at the output to make up for that somewhat. The secondary...
Recent Comments
Update on the Mod-86...
Posted Yesterday at 02:09 AM by abraxalito abraxalito is offline
Yes its constant on...
Posted Yesterday at 01:09 AM by abraxalito abraxalito is offline
Quote:
Originally Posted by abraxalito
Very good points. I
...
Posted 27th February 2015 at 06:06 PM by CharlieLaub CharlieLaub is offline
If the capacitors are...
Posted 25th February 2015 at 05:26 AM by rjm rjm is offline
Very good points. I...
Posted 24th February 2015 at 04:24 AM by abraxalito abraxalito is offline
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