The bass booster speaker system in this post describes how to construct such a circuit without affecting the stereo output or sound quality.
The Concept
The concept is simple; the booster merges the bass signals from the left and right stereo channels and amplifies them.
Then, it reproduces the sound through a standard bass speaker. Because of that, there are many ways to utilize this system.
The simplest design will have the low pass filter connected to an extra mono or stereo amplifier that is rated 40W or more. This amplifier is then played using a speaker enclosure with a decent bass response.
R1 - R5 =470 ohm, 0.5W, 5%
R6 - R7 = 100 ohm, 0.5W, 5%
C1 = 1uF, 200V
C2 = 0.1uF, 100V
C3 - C4 = 0.01uF, 100V
OUTPUT CONNECT TO POWER AMPLIFIER
How to Test
Once you are certain all the electronic components are in their right places, set the wiper RV master volume in the middle of its travel. Ensure not to connect the speakers at this point.
After that, turn on the main 240 V supply and measure the voltage across the speaker terminals. The value should below 0.2 V and if it's more, switch off the supply and thoroughly examine all the connections.
If you do not have a multimeter, connect one speaker wire to one side of the amplifier output and briefly touch the second wire to the other output point.
On good connections, the speaker will not produce any sound or just a faint “click” sound. If the speaker cone immediately jumps away, turn off the supply and examine the connections again.
If the speaker is silent and everything seem OK, use a milliammeter (if you have it) to measure the current in series with one of the speaker wires.
Fine-tune the potentiometer RV master volume until the reading on the ammeter shows 40 mA. If there is no milliammeter, just let RV master volume in the middle position.
Next, attach the lead from the current speakers to the filter input and connect the bass speaker to the booster amplifier.
You may power ON the supply and inspect the entire system. Bear in mind that the sound from the bass booster circuit may be a bit distorted if this is utilized from an independent audio source.
However, if you connect the inputs of the circuit with the terminal of an existing left/right speakers of a ready made stereo system, then it might produce a sound incredibly good and with huge bass level.
How it opperates
Resistors R1 to R4 combine the output from every channel of the present stereo amplifier.
Then, resistors R5, R6 and RV1, in addition to capacitors C1, C2 and C3 create a low-pass filter with a cut-off frequency of about 200Hz. Moreover, it also has 18 dB per octave slope.
To protect the speakers from switch ON spikes and transients, capacitor C4 functions as a high pass filter with roughly 30 Hz.
Figure 1 displays the filter that is intended for use with different amplifiers has a 20 dB attenuator attached before the output potentiometer. This guards the subsequent amplifier against overloading.
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