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Hexasupercap

Posted 30th July 2014 at 09:06 AM by abraxalito
Updated 9th August 2014 at 12:30 AM by abraxalito

Here's a hexacap built with 10F caps, so the total capacitance is 610F. The individual caps have ESRs varying from around 30mohms to 60mhoms - I weeded out those above 60mohms with the aim of getting the ESR (and hence total impedance) below 1mohm for all audio frequencies.

The caps are rated at 2.7V which is plenty enough for powering a stack of TDA1387s. Just they take a while to charge up - with around 500mA being fed in the voltage takes almost an hour to reach 2.7V from cold. I've been forming them up and the leakage current seems to be stabilizing now, around 30mA, or 0.5mA per cap.

Update - I've installed this beneath a stack of 6 TDA1387s and been listening for a couple of days. The long and the short of it is there's now no going back to 'conventional' caps, supercaps are here to stay in my DAC designs. The improvement in SQ is rather hard to describe in words - its lower colouration to the LF which might be described as improved 'weight' or 'authority'....
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Old

Keyboard Short Cuts: Copy, Paste, Cut/Delete, Undo

Posted 30th July 2014 at 06:00 AM by SyncTronX
Updated 30th July 2014 at 06:06 AM by SyncTronX

There are some simple keyboard short cuts
that have been around for a while and work.

You may already know them some of us might
not. They were originally used in the Apple
Computer interface and have been held over
on the windows computer too.

After you select an item by clicking it
or clicking and dragging, then do
one of the following: Undo, Cut, Copy, Paste.

The actions are performed with the keyboard keys,
the lower left side and above the space bar.

The keys are Z X C V .

Use one of these keys with the Ctrl key.

Ctrl + C Copy
Ctrl + V Paste
Ctrl + X Delete
Ctrl + Z Undo

The Ctrl key is located in the lower left corner
of the keyboard.

Use the rolling press to make this work.

First press Ctrl with the little finger, left hand,
hold it down,
then press C key with middle finger,...
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Old

Doing interesting things with electronic keyboards

Posted 30th July 2014 at 01:44 AM by fas42
Updated 30th July 2014 at 11:24 PM by fas42

Provoked into Yet Another Project, fiddling with the Yamaha PSR-6700 Portatone we bought over 20 years ago, for my wife to have fun with. This is a solid unit, quite heavy, well thought of even now, with 76 keys - was top of the range, and was the best sounding of the brands and models we looked at the time, in that type of thing. Sometimes called an arranger keyboard, because it can do fancy backing accompaniments, the one-man band thing ...

For those who are not into such, this is an all in one box, very sophisticated synthesizer with internal amp and speakers. Think of it like a reasonable hifi system, where the source material is computer generated, and can get as fancy and realistic as one wants, especially these days. Even in bygone decades remarkable music was created using such devices - Peter Gabriel's well thought of 4th album, Security, was based extremely heavily on sounds from the Fairlight CMI, an Australian made pioneer of this technology.

As...
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Old

Cheapest 32bit CPU to date...

Posted 22nd July 2014 at 07:22 AM by abraxalito
Updated 22nd August 2014 at 04:17 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.

Update - a price drop just happened on Taobao to a similar board, now down to 9.9rmb - http://item.taobao.com/item.htm?spm=...32&ns=1#detail

Pic attached of this mind-numbingly affordable board.

Aliexpress has the boards I bought now, priced at $6.20 but this includes 'free' shipping - http://www.aliexpress.com/item/stm32...701304725.html
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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

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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Posted in Power chip amps
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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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