2nd order low-shelf filter for bass enhance

[[email protected]]

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:
http://www.beis.de/Elektronik/Filter/ActiveHPFilter.html

 

[[email protected]]

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):
http://img235.imageshack.us/img235/1814/bassenhanceeu3.jpg

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.

 

[john jardine]

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):
http://img235.imageshack.us/img235/1814/bassenhanceeu3.jpg

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.

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

 

[martin griffith]

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

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


martin

 

[Vladimir Vassilevsky]

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):
http://img235.imageshack.us/img235/1814/bassenhanceeu3.jpg

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

http://www.abvolt.com

 

[MooseFET]

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.

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

 

[Don Lancaster]

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

Read my book.


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[[email protected]]

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

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.

 

[MooseFET]

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.

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.