# Chaining filters

Discussion in 'General Electronics Chat' started by Yaşar Arabacı, Dec 8, 2014.

1. ### Yaşar Arabacı Thread Starter Member

Nov 11, 2014
36
0
Hi,

I was wondering how one might separate frequency ranges in an analog audio signal in order to send different ranges to different speakers. My initial thought was, other side of a RC low pass filter must be a high-pass filter since it is basically a frequency dependent voltage devider. Therefore, I tried this circuit;

http://i.imgur.com/mRQEm21.png

V1 is 9V DC source, V2 is 0.5Vp signal source. R2, R3, R5 stands for 8ohm speakers as loads.

According to below chart, my approach seems to work;

http://i.imgur.com/JzuHwwP.png

V(n001), V(n005), V(n007) stands for voltages across R5, R3, R2 respectively.

However, I have two questions;

1) Is this the normal approach to this problem
2) I am getting half the voltage for band pass filter (signal that goes to middle amplifier), is there a solution for this problem?

Edit: By half the voltage, I mean that it's maximum value is 5V, while other outputs can have as much as 10V's

Edit2: I have found model for lm386 on the internet, it is not offical so I can't guarantee it works as intended.

Last edited: Dec 8, 2014
2. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,070
Since the input impedance of a LM386 is >10KΩ, why are you using such low values for the resistors and such large values for the capacitors?

I also question letting the AC source (your input) float with respect to the Ground pin on the LM386. There must be a DC path from the LM386 inputs to its own ground. Look up the LM386 data sheet.

When posting here, put your figures here, not on that POS Imgur site that I have to wait minutes for something to load from there...

Last edited: Dec 8, 2014
3. ### Yaşar Arabacı Thread Starter Member

Nov 11, 2014
36
0
At first, I tried to put filters after IC and before speakers, therefore, I needed resistors <8ohm, when I thought about putting filters before the IC, the idea of changing resistor values didn't occur to me.

Pardon me, but I am quite new to this, do you mean pin 3 of each IC (inn) should be connected directly to ground of my input rather than other pin of cap?

Sorry about that, it is an old habit.

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,070
Pin 2 or Pin 3 should go to the ground as well as one end of your input signal source... Read the data sheet.

The input impedance of the LM386 is 50K, so the RC network could have resistance values up to 5K.

A simple one-pole RC network might not have a sufficiently steep roll-off for good band separation. If you are going to have separate power amps for each speaker, you may want to use opamp active filters to separate the bands....

5. ### crutschow Expert

Mar 14, 2008
16,180
4,322
If you have a single amp then the usual method is to use LC crossover networks at the amplifier output to separate the frequencies to the various speakers such as one of these. RC filters have too much loss for use in this application.
If you have a separate amplifiers for each speaker then you can use RC filters (active filters give better rolloff) to separate the frequencies at the inputs to the amplifiers.