Little low pass help please

[Nordic]

I used WinISD to recommend a filter for a small sub... well I was surprised to see it suggests using a 741 IC...

I built the circuit but it does not sound right yet... I assume I gave bad values for capacitors... I realy just don't know what a good starting point would be...

It sounds mostly cheap but ok, but on hard snare drums it makes a kinda poping sound...

The values for the two resistors are 7.5k and the caps are .22ufd (I had some nice ones, but please advise if I should use a diferent value here... /Me totaly in the dark) this produced a Cutoff of 96Hz, I think I'd like it to cut maybe a bit lower, still hearing just a tad to much of the middle registers comming through... but I get the concept kinda...

This is to feed an IGC LM3875

Any suggestions welcomed...

[lineup]

There are two commonly used filter types.
Butterworth and Linkwitz ( Third 'Bessel' is not used often )
They have a bit different results.
Different slope and phase.

They use different values for resistors and caps
for same cut off frequency.

If you still do not get enough slope, you may have to use 24dB filters.

[poobah]

The design is ok... get rid of the 741 (noise machine).

You could improve the design with 75K & 0.022 uF for the second filter... this will give smoother response.

[Nordic]

Can I stick 5534 or 2 in there?

Its basicaly a blown amp I am trying to bypass. I don't know enough about slopes etc. yet to be able to input usefull data into simulators...

The specs for the amp were as follows... (still same speaker and sealed box)...

frequency range of 30 to 200,
HIGH-CUT FILTER:
Continuously variable from 50-150Hz
HIGH CUT SLOPE:
24dB/oct (IS THIS THE ANSWER?!!!!!!!!!!!!!!!!!)

DIMENSIONS (W x H x D):
9 1/4"" x 14 3/8" x 12 3/8"
WEIGHT:
21 lbs

[lineup]

Originally posted by poobah
The desin is fine... get rid of the 741 (noise machine).

Yes, really.
You should use at least TL071.
Or any other JFET input OP-amp, like OPA134, OPA604 ...

[lineup]

Originally posted by Nordic
Can I stick 5534 or 2 in there?

Sure!
NE5532 is very often used in filters.
It is gain=1 stable.

NE5534 is not same Op-amp as NE5532 - even though people think so!
NE5534 is better performer than NE5532.

When reference to NE5532 is used to talk bad of NE5534, it is very unfair!'
The DUAL version of NE5534 is NE5533
Dual and single NE5533 and NE5534 datasheet

NE5534 will be even better than NE5532,
but remember to use a comp cap, like 22-47pF between pin 5-8.
this is a gain=1 application, and NE5534 will not guarantee be stable, without compensation cap.

[Nordic]

Originally posted by poobah
You could improve the design with 75K & 0.022 uF for the second filter... this will give smoother response.

R2 and C2?

[poobah]

Yes sir,

The second stage is loading the first and will give you a "bump" @ 96 Hz

[poobah]

Nord,

Scratch that... the original is fine... I forgot you have no load!

[Nordic]

What do you mean no load? Input will be from a NE5532 opamp in my Hafler matrix. Output inpedance is 47k if memory serves correctly...

How will I go about getting a 24dB/oct slope?