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December 18, 2018 / consort3

Rumble filter


This circuit is an implementation of an inverse Chebyshev filter with a fast cut-off, by the simple addition of R9 to an equal component 3rd order high pass filter. R3 and R6 are part of the filter network but have been asymetrically split to bias the op-amp at half supply voltage. The values have to be precise, so resistors should be 1% tolerance. Use of only one power supply is seen as a considerable advantage. This is 1 channel, duplicate for stereo.

Close tolerance capacitors are rare. Try the Rapid 08-0314 or 10-5833 for the 470nF. U2 is defined as a LT1057 but that was for Spice modelling convenience. It is LT’s version of the TL072, I would use a NE5532. V3 could be a wall-wart or even a 9V battery. If driving a low impedance C1 might have to be larger. Response is -3dB at 30Hz, -36dB at 12Hz. The circuit could be used to limit sub-sonic excursion on a ported subwoofer.


I used the inverse Chebychev filter to make a Scratch filter.


The red trace frequency response shows the improved attenuation you get by including C4 from the standard 3rd order Butterworth design shown in blue. The -3dB point is 7.85 KHz.


It has been 10 years since I started blogging. The blog seems to have mutated into “alternative techniques for active analogue speakers”.  Once you get a frequency response measuring device and a DCX 2496 you do not the modelling software so much, as you can tweak the response in real time. The response measuring device should be a MLSSA type, so you can gate out room reflections. Fortunately the filters available on the DCX 2496 are standard types which can be easily implemented with active filters. The analog active ones are a economic and technical ”half way house” between passive and digital filters.  I realised that my crossover ideas were usually combinations of 2 ideas.

For active speakers you need lots of amps hence the need for simple, cost effective ones, thus my design of the Darlington one. The most interest in the blog has been in the Darlington amplifier.

My other interests have been reflected in the sub menus shown.

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