Just to clarify - you need to cut everything below 70-80Hz, right?
I use a low-cut filter (18-20Hz, 5-th order) in my system.
See it HERE.
OpAmps may be different (and less expensive) - consider something from this thread: Low noise OpAmps 2014.
I can share the schematic if you are interested. It is easy to re-calculate the R/C values for 70-80Hz...
Cheers,
Valery
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just looking for a simple high pass filter to be used at amp's input, while low freq go to sub. gather that the high pass filter is just some (carefully chosen) caps in a box, but again, any rec's as to who does custom work like that would be a help.
(looking to stay away from opamp based filters)
tia
(looking to stay away from opamp based filters)
tia
There is probably an input dc blocking capacitor and resistor, forming an RC highpass. You could alter the capacitor value and extend it to RC-RC for a steeper slope which would suit closed box roll off of the mains. If they're vented however, you'd need a 4th order filter. And that would require opamps. 4th order RC is either lossy or requires larger capacitor values and normally larger physical size.
People who sell opamps do. TI has a pretty good application brief called "Active Filter Design Techniques" HERE, and there are a few interactive webpage active filter "calculators" that will spit out component values for a filter whose shape you specify. Try the googles.
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