Audio Signal Conditioning Circuit

Worked

flux

Work completed
  • Routed J1/J2 through AC-coupling and RF filters into SW1, and from SW1 into U1/U4 preamp +IN pins; unused inputs tied off.
  • Fanned out 1.65 V bias from U5 to BIAS_NET; wired VR1 wipers into the U1 feedback loops.
  • Added seven 100 nF decoupling capacitors (C1–C7) to power pins of U1, U4, U2, U3, and U5, with returns to ground.
Remaining tasks
  • Implement master volume (VR2) and design selectable 40/80 kHz RC filters; connect to U3 inputs.
  • Finalize 3.3 V buffers in U3 with series resistors, D2/D3 Schottkys, U6/U7 TVS, and F1/F2 PTCs.
  • Prepare schematic for 2-layer PCB: annotate star ground, add routing guidelines, run ERC to clear any airwires.
Success criteria status
  • Nets routed with no airwires: ✅
  • Combo jack to mode switch to preamps: ✅
  • 1.65 V bias and VR1 gain control: ✅
  • Master volume and anti-alias filters: ❌
  • U3 buffers with MCU protection: ❌
  • PCB-ready with star ground: ❌
Recommended next step Proceed to implement the master volume stage and anti-alias filter networks (Plan step 3) to complete the signal path before moving on to MCU protection and PCB layout preparation.
Sign up to send
J1
VR2 WIPER_1 - C8 P1
VR1 WIPER_1 - U1 -IN A
J1 1 - C1 P1
U1 OUT B - VR1 CW_2
J1 1 - C1 P1
J2
VR2 WIPER_1 - C8 P1
U1 OUT B - VR1 CW_2
J1 1 - C1 P1
TP1
J1 1 - C1 P1
J1 1 - C1 P1
J1 1 - C1 P1
L6 P2 - SW1 6
J1 1 - C1 P1
J1 1 - C1 P1
U1 OUT A - VR1 CW_1
U1 OUT A - VR1 CW_1
J1 1 - C1 P1
VR1 WIPER_2 - U1 -IN B
J1 1 - C1 P1
J1 1 - C1 P1
L6 P2 - SW1 6
J1 1 - C1 P1
VR2 WIPER_2 - C9 P1
J1 1 - C1 P1
L3 P2 - SW1 3
TP1
J1 1 - C1 P1
U1 OUT A - VR1 CW_1
J1 1 - C1 P1
U1 OUT B - VR1 CW_2
U1 OUT B - VR1 CW_2
VR2 WIPER_2 - C9 P1
J1 1 - C1 P1
VR1 WIPER_2 - U1 -IN B
L5 P2 - SW1 5
U1 OUT A - VR1 CW_1
C1
Capacitance
100 nF
VR1 WIPER_1 - U1 -IN A
J1 1 - C1 P1
U1
SW1
GND
D2
VR1
VR2
Audio Input for 3.3v ADC thumbnail
Stereo Balanced Audio Front-End for Daisy Seed 2 DFM Platform

Properties

Diagram



  
    
  
  
    
  



""Input Stage""


""Bias & Mid-Rail Distribution""


""Variable Gain Stage""


""Master Volume""


""Anti-Alias Filters""


""Output Buffers""


""MCU Protection & Outputs""


""Power & Decoupling""






































































AC Coupling

AC Coupling

AC Coupling

AC Coupling

AC Coupling

AC Coupling

Biasing

Biasing






























































"Balanced Mic In L (J1)"
"RF/EMI Filter L"
"Mic Preamp L (U1)"
"Instrument In L (J1)"
"RF/EMI Filter L"
"Hi-Z Buffer L (U4)"
"Line In L (J1)"
"RF/EMI Filter L"
"Line Attenuator L"
"Balanced Mic In R (J2)"
"RF/EMI Filter R"
"Mic Preamp R (U1)"
"Instrument In R (J2)"
"RF/EMI Filter R"
"Hi-Z Buffer R (U4)"
"Line In R (J2)"
"RF/EMI Filter R"
"Line Attenuator R"
"Mode Switch SW1 (MIC / INST / LINE)"
"ESD / TVS Protection D1 + TVS"
"1.65V Ref Source"
"U5 OPA188 Buffer"
"1.65V Mid-Rail (BIAS_NET)"
"Preamp Bias Nodes U1/U4"
"Post-Gain Bias Nodes"
"GAIN_A (VR1 Ch1)"
"GAIN_B (VR1 Ch2)"
"VR1 Dual Pot (Preamp Gain)"
"FB_A / FB_B Feedback Nets"
"Post-Gain L"
"VR2 Ch1"
"Post-Gain R"
"VR2 Ch2"
"Volume Controlled Outputs L/R"
"Vol Out L"
"AA RC node_40kHz L"
"AA RC node_80kHz L"
"Vol Out R"
"AA RC node_40kHz R"
"AA RC node_80kHz R"
"AA Filter Select"
"Selected AA Out L"
"U3 Buffer A (3.3V)"
"Selected AA Out R"
"U3 Buffer B (3.3V)"
"Series R + PTC F1 L"
"Schottky Clamp D2 L"
"TVS to 3.3V/GND"
"Daisy ADC D1"
"Series R + PTC F2 R"
"Schottky Clamp D3 R"
"TVS to 3.3V/GND"
"Daisy ADC D2"
"TP1/TP2/TP3 Test Points"
"3.3V Rail"
U3
U2
U5
"12V Rail"
U1
U4
"C1-C7 Local Decoupling"

Pricing & Availability

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Qty 1

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$12.84–$18.47

Digi-Key

$9.20–$10.78

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$35.66–$35.90

Mouser

$46.39–$46.51

TME

$14.52

Verical

$28.03–$44.42

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