Passive EQ for STAX

Posted on Feb 4, 2014

Many audiophiles reject equalizers for various reasons, some of which relate not to the EQ circuit itself (or algorithm) but to the surrounding `glue` of op-amps, transistors, A/D and D/A converters etc. The only `passive` EQ I`m aware of is horribly expensive and is not actually 100% passive - it contains some amplifying glue to restore the signal to a usable level. [Hint: Look up the values of inductors

Passive EQ for STAX
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you might typically find in a speaker crossover. ] Needless to say, these suckers are not shelf items! It would be nice if they were air-cored but some ferrite may be necessary, especially for L1, where I estimate 250 metres of wire could be necessary otherwise. This is not something you want to try and wind by hand. If you can locate a reel of enamelled wire with both ends of the copper sticking out then you should be so lucky. The good news is you don`t need fencing wire for these - even as fine as SWG 34 (or AWG 31 = 0. 23mm diameter) should be OK, as the impedances are quite high and a few ohms of resistance won`t upset things. The inductors should be placed well apart from each other in a metal box. If you don`t have an inductance meter (who does ), the tank circuits L1-C1 and L2-C2 can be tuned with an audio oscillator and a multimeter. The inductors should be in place in the box when you do this. 2. A Lambda response plot produced by Moller et al. from the article "Transfer Characteristics of Headphones Measured on Human Ears", Journal of the Audio Engineering Society, v43, #4, April 1995, p215. Those Toko inductors are a great find! I searched a bit but didn`t turn up anything with those kinds of values, and they are so compact too(!) This involves compromises of course - they are obviously using a very fine guage of wire so the DC resistance is near the top of the tolerable range. [More than 1 ohm per mH would be...

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