2nd order low-shelf filter for bass enhance

How to change a Sallen-Key low pass filter so that it becomes a shelving filter?

I.e. I want it to accentuate the bass frequencies (by 10dB, transfer frequency around 150Hz), all higher frequencies should pass without amplification but no attenuation either.

I found this webpage for dimensioning (using Butterworth characteristics), it dimensions a Sallen-Key filter:

formatting link

Reply to
ugly.creep
Loading thread data ...

I made an attempt to build the filter in one opamp circuit. Simulations in PSpice 9.1 prove that it must work. However, I would like to have someone's feedback on it. Are there any problems expected with this kind of solution?

Here is an image of PSpice schematic + simulation (frequency response):

formatting link

The high-pass part is a Sallen-Key 2nd order filter. The low-pass is a simple bass boost capacitor that I added in the negative feedback. I added a resistor to ground to make this part work. The Sallen-Key filter should still work as a 6dB/octave because in its frequency area, the bass boost filter has become flat.

Could someone please take a look and comment on it?

Thanks, U.c.

Reply to
ugly.creep

It'll work fine. It -was- a SK low pass filter but the heavy massaging you've given it in spice means it's a one off. I.e you'd have a lot of work calculating that particular response shape from scratch :)

--
Posted via a free Usenet account from http://www.teranews.com
Reply to
john jardine

Try Filter Pro software from TI, and it's free

martin

Reply to
martin griffith

This circuit will work for the bass boost with the fixed response. However in most of cases the bass boost has to be made adjustable: the boost frequency, gain and Q should be set independently. In this design, all of the parameters are tightly coupled, so it wouldn't be possible.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

formatting link

Reply to
Vladimir Vassilevsky

I think a number must have been transcribed wrong. The circuit as posted looks to me to be in oscillation.

Reply to
MooseFET

Read my book.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
 Click to see the full signature
Reply to
Don Lancaster

Hi MooseFET.

I think it appears so because of the peak, however, the filter consists of 2 parts really. It won't oscillate because the Sallen-Key filter is safely dimensioned as a Butterworth curve. The lower part around the 390n accounts for the bass boost.

The filter is meant to operate at this fixed setting, btw.

Reply to
ugly.creep

Unless I misread the values in the picture, it certainly isn't Butterworth. The gain of the opamp is just about 4 at the cut off and the resistor ratio is about 1:2.

For the unity gain case, the resistor ratio would be correct for a Butterworth but not for the case of a gain near 4.

Reply to
MooseFET

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.