Circuit Preamplifier 2.1 stereo tone control + subwoofer

2.1 active subwoofer preamplifier

Stereo preamplifier 2.1 , tone control + subwoofer, useful preamplifier circuit to be used in active boxes, combined with power amplifiers. It has a bass filter for the subwoofer channel and a stereo channel with bass/mid and treble tone control. With independent volume adjustment for the satellite speakers and subwoofer.

About the 2.1 Preamplifier

P1 sets the overall volume, C6 couples the audio signal to the IC1A amplifier, configured as inverter and 1.5 gain works with buffer. IC2A forms the tone control with bass and treble option. P2 adjusts the output volume for the satellite speakers. R17 and R18 connect the stereo signal to the amplifier IC3A, configured as non-inverting and gain 11, if necessary you can change the gain. IC3B was a high pass filter with a cutoff frequency of 49Hz, IC4A a low pass filter with a cutoff frequency of 157Hz and IC4B forms a low pass filter with an adjustable cutoff frequency via P6 from 58Hz to 157Hz, P5 adjusts the volume of the bass channel.

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The cut-off frequency can be adjusted according to your needs, for this use circuit calculators with operational amplifiers.

Also get to know our 2.1 amplifiers

Here I used JRC’s original NJM5532 operational amplifier, you can use any dual operational amplifier.

The power supply uses rectifier bridge in DB-1 package and can be DB102, DB103, DB104, DB105, DB106 or DB107. For filtering we used C23, C24, C12, C13, C27, C28, C21, C22, C25, and C26. We used voltage regulators LM7812 and LM7912, optionally you can use 3 mm leds to indicate the power status. The transformer should be a double type from 12 + 12 to 15 + 15 VAC. Avoid using the same transformer that feeds the power amplifier.

This preamplifier can be used with several of our amplifiers posted here. You can reuse burned-out home-theater speakers, with the option of using a subwoofer and two or more satellites.

Schematic of the 2.1 preamplifiers with tone control and bass filter

2.1 Stereo Subwoofer Preamplifier Schematic
2.1 Stereo Subwoofer Preamplifier Schematic

Printed circuit board of the preamplifier with tone control and subwoofer output

Preamplifier Components View Tone Control
Preamplifier Components View Tone Control
Pcb Printed Circuit Board Bottom Part
Pcb Printed Circuit Board Bottom
Pcb Printed Circuit Board Top
Pcb Printed Circuit Board Top
Silk Components Preamplifier 2.1 Subwoofer
Silk Components’ Preamplifier 2.1 Subwoofer

Bill of material to assemble 2.1 stereo preamplifier, tone control + subwoofer

Last Update: 10/21/2022 10:07 AM

Parts Value Description Quantity
1/4W resistors
R1, R4, R5, R9, R10, R13, R14, R29, R30 1K Brown, Black, Red, Gold 9
R2, R11, R17, R18, R26 68k Blue, Gray, Orange, Gold 5
R3, R12, R19, R21 100k Brown, Black, Yellow, Gold 4
R6, R7, R8, R15, R16, R20, R27, R31, R32 10k Brown, Black, Orange, Gold 9
R22 150k Brown, Black, Yellow, Gold 1
R23, R24, R25, R28 6.8k Blue, Gray, Red, Gold 4
C1, C2, C14 47pF (47) Ceramic Capacitor 3
C3, C7 10p (10) Ceramic Capacitor 2
C4, C8 2.2n (222) Film capacitor 2
C5, C9, C15, C16, C17 100n (104) Film capacitor 11
C6, C10 1u (105) Film capacitor 2
C11 10u/25V Electrolytic Capacitor 1
C12, C13 2200u/25V Electrolytic Capacitor 2
C18, C19 220n (224) Film capacitor 2
C20 10n (103) Film capacitor 1
C21, C22 220u/25V Electrolytic Capacitor 2
C23, C24, C25, C26, C27, C28 100nF (104) Ceramic Capacitor
IC1, IC2, IC3, IC4 NE5532N or equivalent Operational amplifier dual 4
IC5 LM7812 12V positive voltage regulator 1
IC6 LM7912 Negative voltage regulator -12V 1
B1 DB107 Bridge rectifier 1
LED1, LED2 Led 3 mm Green or red led 2
P1, P2, P3, P4 50K Double potentiometer 5
P5, P6 50K Simple potentiometer 1
CN1 POWER KRE 3-Way Connector Terminal 5.08 mm 1
CN2 IN JST-XH-03 2.54 mm 3-pin connector or equivalent 1
CN3 OUT JST-XH-03 2.54 mm 3-pin connector or equivalent 1
CN4 SUBOUT JST-XH-03 2.54 mm 2-pin connector or equivalent 1
Solder, Wires, PCB, Box, transformer, etc.

Download files for this assembly, includes Gerber, PNG, PDF, and postscript PCB files.



Buy equivalent board in AliExpress

Aliexpress 2.1 Preamplifier Board
Aliexpress 2.1 Preamplifier Board

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About the author blog author. Electronics technician for the technical school of Brasilia - Brazil. Interested in electronics, circuits and technology in general.

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