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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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DAC filter for discrete buffer

Posted 15th August 2014 at 12:44 AM by abraxalito
Updated 22nd August 2014 at 04:56 AM by abraxalito

Here's the next experiment - a higher working impedance anti-imaging filter which allows operation without any active voltage gain stage following it. Its also one you can build with Mouser parts - Fastron make inductors suitable for this - substitute their 27mH for the 30mH for only a modest degradation in the FR. Or add a Panasonic 2.7mH in series with the 27mH if you'd like to go the whole hog.

The frequency response is -3dB at 18.5kHz and about -55dB by 24.1kHz. Passband ripple is <0.3dB.

Update - after winding all the coils I realized that I don't have a system right now to slot a full bandwidth DAC into - mine at present is fully activated. So to test out the buffer design's audible qualities I need to build a limited bandwidth DAC (for my bass/mid, up to 3.5kHz). Hence another version of the bass/mid LPF is called for, with the highest possible working impedance. Turns out I can wind a 125mH coil with wire which doesn't break too easily (0.13mm dia)...
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