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Active Differential Audio Filters

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Active Differential Audio Filters
Active Differential Audio Filters
In professional audio engineering, it is common practice to implement not only the inputs and outputs as differential stages, but also to design the entire signal processing chain accordingly. High-quality ADCs frequently offer differential inputs, while advanced DACs often provide differential outputs. Leading semiconductor manufacturers specializing in audio electronics supply fully differential operational amplifiers, which enable the realization of suitable filters. This article introduces four PCBs designed for such applications, which can naturally be combined as needed.
EUR

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Materials

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Bill of Materials

Component List: Low-Pass Filter (2.5 kHz)

Resistors

Unless otherwise specified:

Thin-film SMD 0603, 1%
R1 = not fitted *
R2, R3 = 47 kΩ
R4, R5 = 910 Ω
R6, R7, R10…R13, R20 = 1 kΩ
R8, R9, R14, R15 = 470 Ω
R16, R17 = 220 Ω
R18, R19 = 10 kΩ, thick-film

 

Capacitors
C1, C2 = 0 Ω, SMD 1206, *
C3, C5, C6, C9, C11, C12 = 47 nF, SMD 0805, C0G
C4, C10 = 47 nF, SMD 1206 or 0805, C0G
C7, C8, C13, C14 = not fitted
C15…C18 = 22 µF / 20 V, tantalum, SMC-B
C19…C22 = 100 nF, X7R, SMD 0603

 

Semiconductors
LED1, LED2 = LED, SMD 0805
IC1, IC2 = OPA1633 SOIC8

 

Other
JP1, JP6 = 4-pin header, 0.1″ pitch
JP2…JP5 = 3-pin header, 0.1″ pitch
JP7 = 2-pin header, 0.1″ pitch
PCB

 

* see text

Component List: High-Pass Filter (2.5 kHz)

Resistors

Unless otherwise specified:
Thin-film SMD 0603, 1%
R1 = not fitted *
R2, R3 = 0 Ω *
R4, R15, R20 = 1 kΩ
R5, R6, R10…R12, R14 = 51 Ω
R7…R9, R13 = 2 kΩ
R16, R17 = 220 Ω
R18, R19 = 10 kΩ, thick-film

 

Capacitors
C1, C5, C6, C8, C10…C17 = 47 nF, SMD 0805, C0G
C2, C3, C7, C9 = not fitted
C18, C19 = 2× 47 nF stacked, SMD 0805, C0G
C20…C23 = 22 µF / 20 V, tantalum, SMC-B
C24…C27 = 100 nF, X7R, SMD 0603

 

Semiconductors

LED1, LED2 = LED, SMD 0805

IC1, IC2 = OPA1633 SOIC8

 

Other

JP1, JP6 = 4-pin header, 0.1″ pitch
JP2…JP5 = 3-pin header, 0.1″ pitch
JP7 = 2-pin header, 0.1″ pitch

PCB

 

 

* see text

Component List: Band-Pass Filter (800 Hz / 4.5 kHz)

Resistors

Unless otherwise specified: Thin-film SMD 0603, 1%
R1 = not fitted *
R2, R3 = 0 Ω *
R4 = 3 kΩ
R5, R6 = 51 Ω
R7, R8 = 6.2 kΩ
R10..R13 = 1.1 kΩ
R14, R15 = 560 Ω
R16, R17 = 220 Ω
R18, R19 = 10 kΩ, thick film
R20 = 1 kΩ

 

Capacitors

C1, C4, C5, C9…C12 = 47 nF, SMD 0805, C0G
C2, C3, C6, C8, C16, C18 = not fitted
C13…C15, C17 = 22 nF, SMD 0805, C0G
C19…C22 = 22 µF / 20 V, tantalum, SMC-B
C23…C26 = 100 nF, X7R, SMD 0603

 

Semiconductors

LED1, LED2 = LED, SMD 0805

IC1, IC2 = OPA1633 SOIC8

 

Other

JP1, JP6 = 4-pin header, 0.1" pitch
JP2…JP5 = 3-pin header, 0.1" pitch
JP7 = 2-pin header, 0.1" pitch
PCB

 

* see text

 

Component List: SE Input + Low-Pass Filter (22 kHz)

Resistors

Unless otherwise specified:
Thin-film SMD 0603, 1%
R1 = not fitted *
R2, R3 = 100 kΩ
R4, R6, R11 = 1 kΩ
R5 = not fitted
R7, R8 = 3.3 kΩ
R9, R10, R12, R13 = 1.1 kΩ
R14, R15 = 560 Ω
R16, R17 = 91 Ω
R18, R19 = 10 kΩ, thick-film

 

Capacitors

C1, C2 = 100 nF, SMD 1206, C0G
C3, C4 = not fitted
C5 = 8.2 nF, SMD 1206, C0G
C6, C7 = 4.7 nF, SMD 1206, C0G
C8, C9 = 0 Ω
C10…C13 = 22 µF / 20 V, tantalum, SMC-B
C14…C17 = 100 nF, X7R, SMD 0603

 

Semiconductors

LED1, LED2 = LED, SMD 0805

IC1 = OPA2210 SOIC8

IC2 = OPA1633 SOIC8 *

 

Other

JP1, JP2 = 4-pin header, 0.1″ pitch
JP3…JP6 = 3-pin header, 0.1″ pitch
JP7 = 2-pin header, 0.1″ pitch
PCB

 

 

* see text

Component List: Power Supply

Resistors

R18, R18 = 10 kΩ, SMD 0603

 

Capacitors

C19…C22 = 22 µF / 20 V, tantalum, SMC-B
C23…C26 = 100 nF, X7R, SMD 0603

 

Semiconductors

D1, D2 = LED, SMD 0805

IC1 = 7812, TO220

IC2 = 7912, TO220

 

Other

JP1…JP5 = 3-pin header, 0.1″ pitch
PCB

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