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Amplifier-centric two-way XO (and system) design

Posted 3rd July 2014 at 04:30 AM by abraxalito
Updated 5th July 2014 at 02:55 PM by abraxalito

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...
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Old

Just for fun - an ultra-low impedance AIF

Posted 18th June 2014 at 11:40 PM by abraxalito

DIYing high enough Q inductors for anti-imaging filters is a bit of a challenge so here's another way to approach this. I found its possible to build very high Q inductors by simply slipping ferrite beads over a fairly thick copper wire. The limitation though is that the beads I have offer about 1.2uH per bead. So making a ferrite bead version of a 660uH inductor will call for over 500 beads - rather impractical.

To make such a ferrite bead inductor filter a practical possibility its necessary to work at a much lower impedance. I've taken a 1ohm working impedance inititally to develop this filter. Now the largest inductor just needs 10 beads. Given this very low impedance the post-amplifier's noise performance becomes rather a challenge - but a transformer will probably do the trick nicely. I plan to try this with a 1:7 step up trafo and see how it goes.

This kind of filter is probably very suitable for DACs with higher output current - the communications type...
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Old

Tweeter line level passive XO

Posted 13th June 2014 at 04:47 AM by abraxalito
Updated 16th June 2014 at 04:51 AM by abraxalito

I'm really impressed with the bang for the buck with my 228rmb speakers, but have a theory they're rather being limited by their crossover. Especially the first order tweeter crossover which hasn't enough LF rejection.

In search of a steeper XO for the tweeter I've decided to go the whole hog and design a kick-*** filter that'll allow me to fully activate these puppies and see just how much they're limited by their electronics. kinku just pointed me to a filter design program called AADE which I've just finished using to design my first LC bandpass filter.

Its bandpass because I want to stick it straight after the DAC and it needs the anti-imaging function, meaning a steep low pass around 18kHz. The tweeter doesn't need this as they're fairly low on IMD, but the tweeter amp sure benefits from having no ultrasonics. Hence here is my first attempt at a tweeter bandpass filter, to go between the DAC and a dedicated tweeter amp.

For now I'll use the TDA1521...
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Old

Linsley Hood amp on Taobao

Posted 4th June 2014 at 05:27 AM by abraxalito

Looks like a bargain, around $120. Sorely tempted to get one to play with - what do you think ?
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Old

Cheapo passive speakers breaking in

Posted 1st June 2014 at 06:02 AM by abraxalito
Updated 2nd June 2014 at 03:54 AM by abraxalito

A pair of these were delivered yesterday. At first I thought their bass sucked and the top end was too 'phasy' - it was only after a while I realized I'd connected them out of phase

Now they're wired up correctly on my TDA1521 amps, they're starting to come on-stream. I rate them as a bargain at the asking price of 228rmb (around $35).

After they've fully broken in I plan to explore what the lowest hanging fruit is by way of tweaks to the crossover....

Update1 - here's the XO, very simple 1st order. 250uH inductor on the bass (0.1ohm DCR, 6ohm bass/mid) and 1.5uF cap for the tweeter (8ohm). The NP cap for the tweeter has a rather high ESR (3ohms at 1kHz) so there might be some mileage in substituting this for a foil cap.

Plotting this arrangement on LTSpice gives a crossover frequency (if -6dB) around 7kHz which seems a little high. If we were to assume a -3dB crossover (because they're in quadrature for a 1st order) then it would...
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Old

TDA1521 chip amps rock!

Posted 23rd May 2014 at 03:13 AM by abraxalito

Here's my prototype TDA1521 dual mono arrangement - two chips per channel in bridged/parallel, sat atop 400,000uF hexacaps. The neutrality has taken a while to get used to but I'm lovin' em....
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Old

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.

http://www.avsforum.com/t/1511825/go...ne-at-ces-2014

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'. Really? What do you guys think?
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Old

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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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

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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