2.1Channel Low pass filter LPF subwoofer preamp schematic Sallen Key

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Using OPamp NE5532 is Same or Replacement of RC4588D
Schematic- RC4558D/NE5532 Datasheet
Everybody with has a habit on audio sound wants a heavy bass output, The first thing to understand is the basic concept of a subwoofer system. What it is trying to do, and how does it work? Obviously, the fundamental idea is to reproduce low frequencies to get a Heavy BASS output.
Most stereo systems have two output which is in every channel line output (L/R) is there were the main speaker and tweeter/midrange together, yet sometimes four channel stereo. Why not try these subwoofers speaker separated in the main speaker in one connection as well? In some situations, there can be advantages to having 2.1CH stereo.
The Bass sound reflex is deep heavy because there is one speaker connected in subwoofer output, How to do these? You need a three(3) output power amp which is have Left(L), Right(R), Center(BASS) called it 2.1 channel.

The subwoofer speaker is connected to Center output of 3rd power amplifier and the main, tweeter, midrange speaker is connected to (L)(R) output of a power amplifier
The volume gain of Center(BASS) output is separated from the main volume of (L)(R)-satellite speaker
Let me explain these in below,

Simple Block Diagram of 2.1 sounds circuit

The relevance of I want to share to all is How to build a Filtered Low pass circuit?.
In my experience, there is three kinds I know how to build, IC type circuit, Capacitor circuit, Coil circuit.
The Low pass preamplifier is producing Low-pass signal deliver to the Subwoofer power Amplifier.
There are many circuits making low pass filter using preamp ic like IC4558D or NE5532

IC type example of Preamp 5-12vDC Low Pass Signal(LPF) output double supply only

(Without IC)Test Simple Capacitor Low Pass Filtered simple circuit

You can change the value of Mylar capacitor by high to low order, Example is 10uf - 1uf - 0.1uf.
and the resistor value to 220 ohms to 1k ohm, you can add a 104J to the output to make a 3rd order low pass circuit. And see the difference of frequency output for your satisfaction by changing the value.
This Circuit has Fix Gain because there is no Pre-amp connected, But the input of A and B connected to the output of a stereo amplifier of  TDA7297(15W+15W RMS) which provide a gain source deliver the low pass signal to TDA7379(38W+38W)

LET ME EXPLAIN CLEARLY...

The Output of this Circuit has become mono, You need a two class AB Chips.
TDA7379(80W total) or TDA7297(30Watts total) RMS power.

Build a TDA7379 power amp. Then build a TDA7297 power amp, and build a Select your Low pass Filter in circuit here post.
After building these 3, connect the input of the 3rd order Low pass you build to the positive output of TDA7297, And the output 3 order lowpass filter is connected to the input of TDA7379.
The connection of Speaker
The Tweeter and Midrange are connected to TDA7297 Left and Right channel.see fig.1 above
The Two Subwoofer is connected to TDA7379 Bridge, as a result, you created a 2.1 amplifier.

LOW Pass Filtered by OP-Amp IC

Test experiment First of 1/2 IC type

Watch the video below.

Circuit is already done of AMP RC4558D(1/2) only produce LOW PASS but not more produce REVERB DEPTH high cause not amplify the low frequency, Its filter only.

Datasheet schematic- RC4558D Datasheet

TEST experiment Full IC using 4558D REVERB DEPTH BASS FULLWAVE LPF 50HZ LPF

The circuit below is LowPassFiltered BASS powered by RC4558D with some component and I test. You can get pure 50Hz Bass output. Also this is Single ended power supply 5V-12VDC

This Circuit is for Subwoofer Bass Speaker Preamp. It deliver signal to Audio amplifier a Low pass to create a FULL BASS output. The 1st OP amp will amplify the input signal coming from R1/R2 down to 100hz i think. The 2nd OP amp is filter the signal coming to R5 down to 20-50HZ deliver to P1 as volume control.

If you not have Audio Amplifier, You can select circuit here at my POSTED CAR Amplifier 12VDC and connect your LPF as input and lets check the BASS sound if you satisfy it

Watch this Video a Complete layout of Home Made 4000W PMPO Car audio Booster.
In this video is show How to build LOW PASS frequency(LPF), High Pass Frequency(HPF), Build 4 Channel 40 Watts per channel(500W PMPO)

Note: This Circuit is intended as Booster frequency for "Car Audio Player", It is not suitable in headphone output or mobile phone output because signal is weak which is not test but maybe compatible if you combine or remodel the input by normal preamp before this circuit.
If you want a heavy bass output you need a High power amplifier which can drive a Subwoofer speaker not woofer speaker, This is not a same, The subwoofer speaker gives a mass Bass output than normal woofer speaker.
You need to insert this LPF Circuit to the Another power amp (solo) Audio amplifier and you feel the POWER REVERB DEPTH SOUND will Vibrate your chest.

Test experiment of Adjustable 20Hz - 300Hz Low Pass Filter DIY board

Watch the Video of Low pass Filter DIY board using NE5532

Using NE5532 is Same or Replacement of RC4588D. The List of Parts
1. Resistors
10K ohm - 9pcs
220 ohm - 1pc
2. Electrolytic Capacitor
1000uf - 1pc
10uf - 3 pcs
100uf - 1pc
3. Mylar
474J - 2pcs
J100 -1pc
4. Potentiometer
50K - 2pcs
5. NE5532 Chips - 1pc
1pc Diode - In4001

Check Price DIY low pass filter Board

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