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abraxalito abraxalito is online now

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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
    It doesn't have to take the form of a conspiracy, rather a consensus... James H Kunstler

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  • Last Activity: Today 02:11 PM
  • Join Date: 19th September 2007

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http://abraxalito.googlepages.com
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Latest Blog Entry

Posted 22nd July 2014 at 07:22 AM by abraxalito Comments 0
These Cortex M0 modules are 14rmb on Taobao, just over $2 a pop, with more number crunching speed than my first ever PC (40DMIPs).

The CPU is the STM32F030, a 48MHz devuce with limited I/O (I2C, SPI) in a 20 pin TSSOP. The going rate for this chip is 2.4rmb ($0.40).

I have an idea to build a DAC with a handful of these little beauties carrying out some of the filtering.

Posted 21st July 2014 at 11:59 PM by abraxalito Comments 0
Seeing as building hexacaps with wire is very time consuming, I'm investigating ways to get the production cost down. Here's my first attempt at a PCB hexacap, using 2oz copper - I did the layout on EasyEDA - Web-Based EDA, schematic capture, spice circuit simulation and PCB layout Online

Once I've ironed out the minor errors on the groundfill I'll make the PCB public so anyone can order up their own. There are 127 caps on this board giving a 50Hz capacitive reactance just under 8mohms.

Posted 11th July 2014 at 12:11 AM by abraxalito Comments 17
Posted in Power chip amps
Very interesting paper which I'd not come across before which poses about as many questions as it answers. Thanks to Bob Cordell mentioning it in his book, here's the link :

http://www.eetasia.com/STATIC/PDF/20...URCES=DOWNLOAD

Compare the FFT in fig3 (closed loop) with fig4 (open loop) in the text - which do you think will sound better?

Here's my take on what the paper is claiming, FWIW. That PSRR measurements when the amp has a BTL (balanced) output aren't appropriate because there is output stage cancelling of them. My first head-scratch moment came because this is true of other amp topologies too, not just classD as BTL outputs are very much alive and well in NXP's range of chipamps for automotive use. So why restrict this to just classD?

Secondly what's the argument that PSRR in BTL amps isn't appropriate? They seem to be saying (though they don't express this very clearly) that whilst output stage...

Posted 3rd July 2014 at 04:30 AM by abraxalito Comments 5
Posted in Uncategorized
The traditional view is that the speakers are the weakest link of the audio system and hence they're not really designed with amplifiers in mind. Why make amp design easier when speakers are plenty hard enough to get right?

In my experience speakers don't contribute very much to the listening satisfaction. They're more a matter of taste, but a much better speaker can't undo the faults of an amplifier (or DAC for that matter). That's not to say some speakers don't sound better than others - I mostly prefer my Paiyons to the much cheaper Denons but their 'betterness' is orthogonal to the way to the manner DACs and amps sound better. Electronics has had the biggest impact on my listening satisfaction so far so here is an XO designed to make the electronics' job as easy as possible.

Given that the critical parameters of an amp designed for listener satisfaction aren't THD+N and FR, rather multitone IMD (aka MTPR) and PSRR it makes sense that an amp is given the narrowest...

Posted 22nd June 2014 at 04:24 AM by abraxalito Comments 7
Hexacaps have their limitations - they provide a great low impedance for lower freqs but according to my LCR meter, turn inductive for frequencies in the mid-single digit kHz. Which is about the lower edge of the passband for a tweeter. So what to do to get a low impedance power supply to a DAC chip from 4kHz and up? Here's my first attempt - there are 7 TDA1387s each sandwiched between two low ESR 4700uF lytics. Sandwiching them together is an attempt to get the inductance as low as possible - the loop area can't practically get any smaller than this. Getting the wires in has tested my patience and that's even before powering the beast up....

Update - well I could have been knocked over with a feather - this worked first time I plugged it in. So now I'm thinking about how to build a markII version, considering if I can get more decoupling close in....
Oh I'm now not sure that my bandpass tweeter filter is really delivering the goods as per its simulation. Connecting...
Recent Comments
I saw the same amp on...
Posted 18th July 2014 at 02:47 AM by zog666 zog666 is offline
Hi miklos, no worries...
Posted 16th July 2014 at 10:56 PM by abraxalito abraxalito is online now
Richard,
I'm sorry...
Posted 16th July 2014 at 06:39 PM by miklos miklos is offline
If a normal volume control...
Posted 14th July 2014 at 12:22 AM by fas42 fas42 is offline
Perhaps you are assuming...
Posted 13th July 2014 at 01:00 PM by abraxalito abraxalito is online now
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