Circuit Preamplifier 2.1 Stereo Tone Control + Subwoofer

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.

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

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

Preamplifier Components View Tone Control

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
Capacitors
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
Semiconductors
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
Miscellaneous
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.

Download

Mirror

Buy equivalent board in AliExpress