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Power supply craziness Lowest possible low-frequency impedances
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I found some more suitable EDLCs

Posted 25th August 2014 at 07:09 AM by abraxalito
Updated 26th August 2014 at 08:52 AM by abraxalito

Many hours can be whiled away trawling through stuff on Taobao - most recently I've been browsing the selection of electrical double layer caps (aka EDLCs, supercaps).

I looked at supercaps many years ago when they first showed up in the Farnell catalogue, initially they were designed for back-up memory purposes and always had very high ESRs so weren't much good for power supplies where any kind of current is needed. That seems to have changed and now the caps are finding their way into all kinds of energy storage applications where high pulse currents are required. ESRs have dropped to where they're attractive for audio applications which call for a really stiff power supply down to low frequencies.

The current crop (in the pic) are made by Samwha (a Korean firm) and are really nice and affordable here - 4.5rmb a piece (about $0.70). That's for a 2.7V 100F size which comes in a 22mm diameter can, 45mm tall. A 7cap hexacap packs about the same energy and roughly...
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Old

Hexasupercap

Posted 30th July 2014 at 10:06 AM by abraxalito
Updated 9th August 2014 at 01:30 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

Ziggurat passive shunt for chipamp

Posted 5th May 2014 at 05:34 AM by abraxalito
Updated 23rd May 2014 at 01:34 AM by abraxalito

Two tiers in order to achieve the lowest ESR - top is using 4700uF and bottom, 15,000uF. Total around 0.8F, 25V.

I plan to try this out first with my TDA8566 but that's limited to 18V so if that sounds promising I'll look for a new chip which can handle the full 25V supply capability.

Update1 : Wired the top tier only underneath my new TPA3116 class D amp board from Taobao. Seems here the dynamics aren't limited by the capacitance on the output stage supply, rather on the analog supply (pin17 of the TPA3116) which goes to an internal LDO regulator. No amount of capacitance on this pin (I went up to 100,000uF) gives the chip the LF dynamics of my class AB amp so I've been off in search of a class D chip which doesn't have an internal reg so might be amenable to a hexacap on its supply...

Update2 - NXP's TDA8932 is on order now - this is a chip which can be DIYed because its in a manageably small SO32 package, so no need to order up an eval board. Over...
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Old

One Farad capacitor array

Posted 3rd April 2014 at 04:08 AM by abraxalito
Updated 4th May 2014 at 05:53 AM by abraxalito

This array of 127 10,000uF caps measures -j2.9mohms at 50Hz which I reckon makes it comfortably over 1F in capacitance. ESR is 1mohm @ 50Hz.

The individual caps were measuring on average 8,500uF. Although they're marked 10V (the brand is ChengX a slightly shady Chinese one) they're not good for anywhere near this voltage. I reckon they're in reality 6.3V and they seem to have decently low leakage at this working voltage. I shall be using them at 5V or below.

Update1 - seems I wasn't using enough copper in the wiring. I've now built a second one with 2.5mm2 wiring around the loops and 1.5mm diameter cross links and ESR is down to 0.5mohm @ 50Hz now, decreasing at higher freqs. I have enough caps left for a third one...

Update2 - now the first array has a basement level giving 2.1F total with ESR below 0.4mohms @ 50Hz. There are six paralleled TDA1387s atop the combined hexagons giving unprecedented LF dynamics. Amp long, long overdue for an upgrade.......
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