Since we are straying off topic a bit, is it possible to limit the low-end frequency response of an amp without limiting bandwidth at the other extreme? The reason for my question relates to driving a set of small monitors that are not capable of producing deep bass. An example is the GR Research Criterion which uses a 5.25" Eton midbass with an F3 of 58hz. I would like to prevent frequencies below 50 hz from getting to the speaker. It plays beautifully down to this point, and I'd like to keep frequencies lower than this from mucking up the driver's excellent excursion. I don't like the commonly used methods like electronic crossover's, or large capacitors.
In the past I've used small value caps placed between the preamp and amp to filter out low-frequencies, and this has worked ok. I then used a second output from the preamp without the limiting caps to send a full frequency signal to a powered subwoofer using its low-pass filter to shut out the high frequencies.
But I was wondering if a sonically more transparent approach would be to modify the amplifier's low frequency range.
Any thoughts on this?
What you are saying is that you want a high pass filter, one which would filter out below a certain point, but would pass all above that point.
Of course it can be done. For example, you could exchange the capacitor at the input of your power amp with the same type, but smaller value. This would do the trick. Just which type I can't say without seeing the schematic and doing some maths.
As an example, say your input impedance is 47K, and say your current input DC blocking cap is say 100uF. The turnover frequency would be 0.22 Hz. If you were to reduce this cap to say 2.2uF, this would move to 1.54 Hz, and further reducing it to say 0.1uF would move this to about 39 Hz. If you were to insert a high quality film or polycarbonate cap, you'd gain in overall sound quality as well.
However, Jerry, I must warn you that as any filter, so this filter also would affect your overall phase response with unpredictable results. For example, while you may remove frequencies below 39 Hz, you may also find that your remaining bass has gone soft and mushy, or even that your midrange response is not what it should be, or used to be.
Beware of filters, they are always a problem, no matter how well designed and made of which components.
Obviously, my advice to you is to let mother Mary come to you, speaking words of wisdom - let it be, let it be.
Cheers,
DVV
