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Cheapest 32bit CPU to date...

Posted 22nd July 2014 at 07:22 AM by abraxalito

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.
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Old

First prototype PCB-based hexacap

Posted 21st July 2014 at 11:59 PM by abraxalito

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.
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Old

FB experiment

Posted 21st July 2014 at 02:51 AM by Ceglar

FB only to G1. cap length reduced to 1mm on heater pins. KP now across Rk. Rk still 41R. (82//82)
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Old

Multi Channel Amplifier with DSP Crossover - Retro styling

Posted 13th July 2014 at 02:26 AM by googlyone

What sort of amplifier do you build to go with a funky retro subwoofer and "Ikea Salad Bowl" speakers?

How do you reconcile this with the fact that you have a "metric shitload" of DSP stuff laying around?

I have run into this problem, and concluded that I need to mash these into something that is not new and higher tech than old style.

This has resulted in me trying to train smash "new and old" into what I am hoping will be a retro styled, but thoroughly high tech-on-the-inside amplifier. (Stopping short of going class - D which I hold aesthetic objections against).

So lets get started with the basics. The amplifier will not be square - it will be a parallelogram...

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And to follow up with my (albeit young) recollections of the 1970's, it CANNOT be black.

This amplifier needs to be the most acid driven shade of orange that I can find....
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Old

The real story about closed vs open loop class D amps

Posted 11th July 2014 at 12:11 AM by abraxalito
Updated 23rd July 2014 at 09:51 AM by abraxalito

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...
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Old

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

Tweeter DAC

Posted 22nd June 2014 at 04:24 AM by abraxalito
Updated 25th June 2014 at 05:49 AM by abraxalito

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...
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Old

DIY wooden_ rod_tonearm 17"

Posted 20th June 2014 at 08:14 PM by suwaned (tube audio friends suwaned)
Updated 21st July 2014 at 07:05 PM by suwaned

I have planning make a long wooden tonearm.

I have TA Technics as apart
I split apart and i put only Pivot.
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i made wooden rod for replace .

problem counter weight Technics light. and need more weight for balance.

Made counter weight from Bronze 220 mg.
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Distance Pivot to spindle new TA 17"
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try install to my TT not fixed and
Wooden TA on the track with cartridge MM Shure.
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outsite place, DIY wooden TA 17" wiht alum stand of pivot and arm base from wood.
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It's very Long TA extraordinary . and i think this have little error track than 9"

wacth " test DIY tonearm wooden rod !&" on the track. Test2 DIY Tonearm 17"_wooden rod - YouTube...
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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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