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Force/sense shunt

Posted 24th April 2013 at 08:35 AM by abraxalito
Updated 24th May 2013 at 03:59 AM by abraxalito (Added pics of prototype fs-shunt. Added noise update.)

I'm a recent convert of the lowest possible impedance of power supply based on my experience of adding caps to my chipamp. So I figure the signal stages can't be harmed by reducing their supply impedance either, particularly at LF.

I note there are a few aftermarket regulators around - I had a look at Paul Hynes and Belleson in the past few days. They're a bit pricey for my tastes, given the cost of the components they're using can't be over single digit $ so I've had a look at "doing it at home, only cheaper".

First off, a simple TL431 is about the best bang for the buck achievable, as the part here is 0.2rmb. But the dynamic impedance is typically 0.2ohms and I was hoping and aiming to go a bit lower than this - perhaps an order of magnitude lower, to around 10mohms. Lower than this and the resistance of the PCB tracks come into play and its also very hard to maintain such a low impedance beyond the audio band as cap ESRs (for the best ones) are of...
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Old

Active elliptic - practical implementation

Posted 20th April 2013 at 09:33 AM by abraxalito

Here's the first channel under construction on 2mm pitch double-sided proto board. The opamps in this instance are AD8014 in SOT23-5 packages, hence the choice of the 2mm pitch board. Power supplies will go on another board to be attached to the reverse side.
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Old

Active elliptic anti-imaging filter

Posted 20th March 2013 at 03:18 AM by abraxalito
Updated 20th March 2013 at 03:30 AM by abraxalito (Added FR)

Passive filters rock for SQ, no doubt about it but I'm still curious how good sounding an active DAC I/V post filter might be. So I've figured out an almost equivalent FR active version of my 7th order LC elliptic filter. This active elliptic has been designed using LTSpice's FilterCad program giving the pole/zero positions, then the Williams handbook of filter design helped me translate those numbers into a working circuit. Its using what Williams calls the VCVS 2nd order section based on a twin-T network to realize the zeroes.

My first attempt at an active elliptic filter was using gyrators but that proved very hard (practically impossible) to get stable with CFB opamps due to their HF gain peaking. VFB opamps I ruled out at the start for inadequate SQ - its not hard to make gyrators stable with them. Hence this approach which promises to work with CFBs though I'd guess I'll probably need to add series Rs between the stages in practice. Nothing built yet but thought I'd...
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Old

What is dynamics?

Posted 5th March 2013 at 02:02 AM by abraxalito
Updated 11th March 2013 at 06:35 AM by abraxalito

Fascinating discussion going on about the nature of 'dynamics' over on this thread : http://www.diyaudio.com/forums/multi...nger-what.html

Pano writes (post 1174):

There is a consistency across several decades and cultures that high efficiency speakers sound more dynamic than low efficiency. That's a common subjective assessment, so we might ask "why?"

I'm not going to chip in on that thread because I have bigger fish to fry, but ISTM they're all barking up the wrong tree. That's because the question itself isn't quite posed correctly even though its a great start. Nobody listens to speakers alone, they're always powered by amplifiers. The answer to dynamics lies in amplifiers, not speakers. Put another way 'Its the electronics, stupid!'.

Higher efficiency speakers tax amplifiers (here meaning their power supplies in the main) much less - so there's no way to do an apples-apples comparison...
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Old

Line input RF reject filter

Posted 19th February 2013 at 07:24 AM by abraxalito
Updated 26th February 2013 at 03:09 AM by abraxalito (Added zoomed passband plot)

I've only simmed this so far, no listening tests. The aim here is to have a passive filter which works into a line level impedance (i.e. 10k or greater) and which gives a decent amount of RF rejection without compromising SQ. I plan to incorporate it behind the RCA input jacks of my chipamp.

Design-wise, it started life as a simple 2nd order filter with single series L and shunt C. But when it came to wind the inductor I didn't have a wire diameter small enough to make the required value (44mH). So I split up the inductor into 2 * 22mH and then couldn't resist hanging a cap off the centre tap. The result has turned more into an over-damped elliptic with a higher corner frequency than the original, but with an impeccable phase response to 20kHz. The elliptic-type plot comes about because of the SRF of the two inductors (around 350kHz).

Since fas42 remarked on the phase performance, I've added the group delay plot for the passband. Almost pure time delay of...
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Old

High-end chipamp build project

Posted 24th January 2013 at 07:21 AM by abraxalito
Updated 15th February 2013 at 05:12 AM by abraxalito

Go here : Possibly the most frugal high-end sounding amp?

If you have comments, feedback, critique or improvements and don't want to put it on that thread, feel free to leave it in the comments here.

Here are the first measurements - the Nitro amp being fed by the Ozone DAC with a six-tone multiple, peak digital level -20dB. Peak output power around 100mW in an 8R speaker (connected for this test). It looks from this that the datasheet is a little pessimistic on THD, though here I'm measuring the TDA8566, not the 8561. No measurement graphs are presented in the 8566 DS and the 8561 only has plots for 2R and 4R loads, not 8R.

Schematic now added. BOM here : https://docs.google.com/spreadsheet/...Hc&usp=sharing

Additional schematic showing how to use TDA8566Q in place of TDA8561Q as the latter isn't available from Mouser. Mouser only has fewer than 300 TDA8566Q in stock so best...
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Old

Noise modulation and subjective performance of DACs

Posted 25th December 2012 at 04:22 AM by abraxalito
Updated 25th March 2014 at 07:44 AM by abraxalito

I've recently come to the view that the best metric of SQ in DACs is noise modulation, however as yet I'm unclear how best to go about making the measurement. Stereophile tried, and here's what they did - Noise, Modulation, & Digital/Analog Conversion | Stereophile.com

Robert Harley reports no correlation with listening so I deduce from this that the test method isn't looking for the right thing. My own gut feel is we need a multitone test waveform rather than a single sinewave as a sinewave has a crest factor quite unlike music and if a sine provoked the condition we'd see it on the 'N' part of a THD+N vs level test.

Having said that, of course we do indeed see something weird going on - on Weiss Medea's implementation of the ESS Sabre. The THD+N plot versus level shows kinks which most certainly are not increased THD at various levels, so can only be noise floor modulation. See a critique I made on WBF here - http://www.whatsbestforum.com/showth...l=1#post133677...
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Old

Digital that sounds like analog

Posted 10th December 2012 at 03:18 AM by abraxalito
Updated 15th February 2013 at 05:11 AM by abraxalito

For those who missed Frank (fas42)'s link on a thread I started then here's where I'm continuing my minimal oversampling DAC developments for the time being : Digital that sounds like analog
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Old

NXP's innovation in smart phone sound - any implication for the high-end?

Posted 2nd August 2012 at 05:13 AM by abraxalito

EET seems to be on a run of interesting articles of late - and here's the latest, about NXP's latest digital amp for smartphone speakers:

Achieving loud, rich sound from micro speakers

So yeah, smartphones are a long way from the high-end you say, so why talk about this at all? Well one sentence at the end caused me to pause and wonder how long before this kind of technology gets used where sound quality (rather than quantity) is paramount. I quote:

This leap in performance illustrates an important design trend. The days of stand-alone amplifiers and converters designed in isolation have gone.

The writer has put his finger on a major reason why the high-end of audio is a relatively stagnant pool for innovation. Pretty much everything's designed in isolation - players, amps, speakers. What if those days really are coming to an end, not just in smartphones but in quality audio too? Smartphones have the volume so there's economic...
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Old

Cirrus now Apple's poodle

Posted 1st August 2012 at 04:53 AM by abraxalito

Cirrus (familiar to us in the audio world as a major ADC/DAC and codec supplier, formerly Crystal Semiconductor) has engineered itself into a tight corner by having over half its sales come from Apple - but its not permitted to mention its largest customer by name due to Apple's draconian NDA.

I wouldn't say things are looking very bright for Cirrus - to be that dependent on one single customer who is that much more powerful than you and a known corporate bully strikes me as poor strategic thinking.

Apple captive Cirrus gagged
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