# Audio Input for 3.3v ADC ## Description Stereo Balanced Audio Front-End for Daisy Seed 2 DFM Platform ## Project Details - **Owner:** alecdvor - **Created:** 12/15/2025 - **Last Updated:** 12/15/2025 - **Visibility:** Public - **System Architecture:** ```mermaid flowchart TD subgraph A [Input Stage] MIC_IN_L["Balanced Mic In L (J1)"] -->|AC Coupling| RF_MIC_L["RF/EMI Filter L"] --> MIC_PRE_L["Mic Preamp L (U1)"] INST_IN_L["Instrument In L (J1)"] -->|AC Coupling| RF_INST_L["RF/EMI Filter L"] --> INST_BUF_L["Hi-Z Buffer L (U4)"] LINE_IN_L["Line In L (J1)"] -->|AC Coupling| RF_LINE_L["RF/EMI Filter L"] --> LINE_ATT_L["Line Attenuator L"] MIC_IN_R["Balanced Mic In R (J2)"] -->|AC Coupling| RF_MIC_R["RF/EMI Filter R"] --> MIC_PRE_R["Mic Preamp R (U1)"] INST_IN_R["Instrument In R (J2)"] -->|AC Coupling| RF_INST_R["RF/EMI Filter R"] --> INST_BUF_R["Hi-Z Buffer R (U4)"] LINE_IN_R["Line In R (J2)"] -->|AC Coupling| RF_LINE_R["RF/EMI Filter R"] --> LINE_ATT_R["Line Attenuator R"] SW_MODE["Mode Switch SW1 (MIC / INST / LINE)"] RF_MIC_L & RF_INST_L & RF_LINE_L --> SW_MODE RF_MIC_R & RF_INST_R & RF_LINE_R --> SW_MODE ESD_JACK["ESD / TVS Protection D1 + TVS"] MIC_IN_L & MIC_IN_R & INST_IN_L & INST_IN_R & LINE_IN_L & LINE_IN_R --> ESD_JACK end subgraph B [Bias & Mid-Rail Distribution] RAIL_REF["1.65V Ref Source"] --> U5_BUF["U5 OPA188 Buffer"] U5_BUF --> BIAS_NET["1.65V Mid-Rail (BIAS_NET)"] BIAS_NET -->|Biasing| PREAMP_BIAS["Preamp Bias Nodes U1/U4"] BIAS_NET -->|Biasing| POST_GAIN_BIAS["Post-Gain Bias Nodes"] end subgraph C [Variable Gain Stage] MIC_PRE_L --> GAIN_A_NET["GAIN_A (VR1 Ch1)"] MIC_PRE_R --> GAIN_B_NET["GAIN_B (VR1 Ch2)"] GAIN_A_NET & GAIN_B_NET --> VR1_GAIN["VR1 Dual Pot (Preamp Gain)"] VR1_GAIN --> FB_NETS["FB_A / FB_B Feedback Nets"] end subgraph D [Master Volume] PREAMP_OUT_L["Post-Gain L"] --> VR2_L["VR2 Ch1"] PREAMP_OUT_R["Post-Gain R"] --> VR2_R["VR2 Ch2"] VR2_L & VR2_R --> VOL_OUT["Volume Controlled Outputs L/R"] end subgraph E [Anti-Alias Filters] VOL_OUT_L["Vol Out L"] --> AA96_L["AA RC 40kHz L"] VOL_OUT_L --> AA192_L["AA RC 80kHz L"] VOL_OUT_R["Vol Out R"] --> AA96_R["AA RC 40kHz R"] VOL_OUT_R --> AA192_R["AA RC 80kHz R"] SW_AA["AA Filter Select"] AA96_L & AA192_L --> SW_AA AA96_R & AA192_R --> SW_AA end subgraph F [Output Buffers] SW_AA_L_OUT["Selected AA Out L"] --> BUF_L["U3 Buffer A (3.3V)"] SW_AA_R_OUT["Selected AA Out R"] --> BUF_R["U3 Buffer B (3.3V)"] end subgraph G [MCU Protection & Outputs] BUF_L --> SERIES_R_L["Series R + PTC F1 L"] --> SCHOTTKY_L["Schottky Clamp D2 L"] --> TVS_L["TVS to 3.3V/GND"] --> ADC_L["Daisy ADC D1"] BUF_R --> SERIES_R_R["Series R + PTC F2 R"] --> SCHOTTKY_R["Schottky Clamp D3 R"] --> TVS_R["TVS to 3.3V/GND"] --> ADC_R["Daisy ADC D2"] TP_NETS["TP1/TP2/TP3 Test Points"] PREAMP_OUT_L & PREAMP_OUT_R & BUF_L & BUF_R --> TP_NETS end subgraph H [Power & Decoupling] V3V3["3.3V Rail"] --> U3 & U2 & U5 V12["12V Rail"] --> U1 & U4 U1 & U3 & U4 & U5 & U2 --> DECOUPLING["C1-C7 Local Decoupling"] end RAIL_REF --> U5_BUF ``` - **Layout Guidance:** Two-layer PCB layout guidelines: (1) Use star ground topology: bring all local grounds (input jack shields, preamp grounds, buffer grounds, TVS/Schottky/PTC grounds, and decoupling capacitor returns) back to a single star point near the Daisy Seed ground/V3V3 return; avoid daisy-chaining sensitive analog grounds through high-current paths. (2) Keep all RC networks feeding the ADC (anti-alias resistors/caps, series protection resistors, and any small RC to ground) as close as possible to the ADC connector/test headers; minimize trace length from the last op amp output to these RC elements and from RC to ADC pin. (3) Surround high-impedance and bias-sensitive nodes (op amp +IN/-IN pins, BIAS_NET distribution, VR1 wipers, VR2 wipers, and the anti-alias RC nodes) with guard ground copper on both layers where possible, tied to the local analog star ground; use short stubs and avoid running fast digital or switching traces parallel to these nodes. (4) Reserve a mostly solid ground plane on the bottom layer, with only short, unavoidable breaks; route noisy or digital nets on the top layer where they do not cross under sensitive analog nodes. (5) Place decoupling capacitors (C1–C7 and others) tight to their respective IC power pins, with the shortest possible return path into the ground star region to reduce loop area. (6) Keep input jack shield/ground pads referenced to the analog ground star with short, wide traces; avoid returning them through the digital/MCU ground section. - **Stars:** 1 ## Key Components ### D1 — [WE-TVS-82400102](https://www.flux.ai/kicad-part-library/we-tvs-82400102~vb9.md) - Role: Protection - Datasheet URL: https://www.we-online.com/components/products/datasheet/82400102.pdf - Package or Case Code: SOT-23-6 - Manufacturer Part Number: WE-TVS-82400102 - Manufacturer Name: Texas Instruments Inc. - Role Details: ESD protection for J1 TIP and RING input nets **Pins:** - ~ [pin 1] - ~ [pin 3] - ~ [pin 4] - ~ [pin 5] - ~ [pin 6] - ~ [pin 2] ### D2 — [SS14](https://www.flux.ai/jecstronic/ss14~ri4.md) - Part Type: Diode - License: https://creativecommons.org/licenses/by/4.0/ - Role Details: Series Schottky diode for part U3 output channels - Manufacturer Name: Slkor(SLKORMICRO Elec.) - Datasheet URL: https://datasheet.lcsc.com/lcsc/1912111437_Slkor-SLKORMICRO-Elec--SS14_C444721.pdf - Role: Protection - Manufacturer Part Number: SS14 **Pins:** - Anode [pin A] - Cathode [pin C] ### D3 — [SS14](https://www.flux.ai/jecstronic/ss14~ri4.md) - Manufacturer Name: Slkor(SLKORMICRO Elec.) - Part Type: Diode - License: https://creativecommons.org/licenses/by/4.0/ - Manufacturer Part Number: SS14 - Role: Protection - Role Details: Series Schottky diode for part U3 output channels - Datasheet URL: https://datasheet.lcsc.com/lcsc/1912111437_Slkor-SLKORMICRO-Elec--SS14_C444721.pdf **Pins:** - Anode [pin A] - Cathode [pin C] ### D4 — [WE-TVS-82400102](https://www.flux.ai/kicad-part-library/we-tvs-82400102~vb9.md) - Role Details: ESD protection for J2 TIP and RING input nets - Datasheet URL: https://www.we-online.com/components/products/datasheet/82400102.pdf - Manufacturer Part Number: WE-TVS-82400102 - Package or Case Code: SOT-23-6 - Manufacturer Name: Texas Instruments Inc. - Role: Protection **Pins:** - ~ [pin 1] - ~ [pin 3] - ~ [pin 4] - ~ [pin 5] - ~ [pin 6] - ~ [pin 2] ### F1 — [1206L020YR](https://www.flux.ai/adrian95/1206l020yr~xmv.md) - Manufacturer Part Number: 1206L020YR - Manufacturer Name: Littelfuse Inc. - Datasheet URL: https://www.littelfuse.com/media?resourcetype=datasheets&itemid=2b6a1515-d4ee-4c83-8bd4-152b4901b8f5&filename=littelfuse_ptc_1206l_datasheet.pdf - Part Type: Fuse - Role: Protection - Role Details: Optional PTC fuse for U3 output channel nets - License: https://creativecommons.org/licenses/by/4.0/ **Pins:** - P1 [pin 1] - P2 [pin 2] ### F2 — [1206L020YR](https://www.flux.ai/adrian95/1206l020yr~xmv.md) - Role Details: Optional PTC fuse for U3 output channel nets - Datasheet URL: https://www.littelfuse.com/media?resourcetype=datasheets&itemid=2b6a1515-d4ee-4c83-8bd4-152b4901b8f5&filename=littelfuse_ptc_1206l_datasheet.pdf - Part Type: Fuse - Manufacturer Name: Littelfuse Inc. - Manufacturer Part Number: 1206L020YR - Role: Protection - License: https://creativecommons.org/licenses/by/4.0/ **Pins:** - P1 [pin 1] - P2 [pin 2] ### J1 — [NCJ6FI-V](https://www.flux.ai/adrian95/ncj6fi-v~kry.md) - Mount: Through Hole - Role Details: Balanced stereo audio input - Package or Case Code: CONN-TH - Manufacturer Part Number: NCJ6FI-V - Package: 6 terminal Thru-Hole - Part Type: Connector - Role: Connector - Manufacturer Name: Neutrik - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.mouser.com/datasheet/2/289/ncj6fi-v-2-1854034.pdf **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - G [pin 4] - R [pin 5] - S [pin 6] - T [pin 7] ### J2 — [NCJ6FI-V](https://www.flux.ai/adrian95/ncj6fi-v~kry.md) - Role: Connector - License: https://creativecommons.org/licenses/by/4.0/ - Manufacturer Part Number: NCJ6FI-V - Datasheet URL: https://www.mouser.com/datasheet/2/289/ncj6fi-v-2-1854034.pdf - Part Type: Connector - Role Details: Balanced stereo audio input - Manufacturer Name: Neutrik **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - G [pin 4] - R [pin 5] - S [pin 6] - T [pin 7] ### SW1 — [DSHP03TS-S](https://www.flux.ai/lcsc/dshp03ts-s~wwpc.md) - Part Type: Switch - Mount: Surface Mount - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2110151630_XKB-Connection-DSHP03TS-S_C319051.pdf - Package: SW-SMD_DSHP03TS-S - Throw Configuration: SPST - Number of Position: 3 - Manufacturer Part Number: DSHP03TS-S - Product Info Url: https://lcsc.com/product-detail/_XKB-Enterprise-DSHP03TS-S_C319051.html - Role: Switch - Operating Temperature: -20~+70℃ - JLCPCB Part Class: Extended Part - LCSC Part Number: C319051 - Package or Case Code: SW-SMD - Voltage Rating: 24V - Current Rating: 25mA - Role Details: Mode selection - Manufacturer Name: XKB Connectivity(中国星坤) **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] - 5 [pin 5] - 6 [pin 6] ### TP1 — [Pin Header 01x06 2.54mm Vertical](https://www.flux.ai/vasy_skral/pin-header-01x06-254mm-vertical~jyw.md) - Role Details: Test point access - License: https://creativecommons.org/licenses/by/4.0/ - Role: Connector - Package: 1x06 2.54mm - Mount: Through Hole - Package or Case Code: CONN-TH - Connector Type: Headers and Wire Housings - Connector Pitch: 2.54mm - Connector Positions: 6 - Part Type: Connector **Pins:** - Pin_1 [pin 1] - Pin_2 [pin 2] - Pin_3 [pin 3] - Pin_4 [pin 4] - Pin_5 [pin 5] - Pin_6 [pin 6] ### TP1 — [Pin Header 01x06 2.54mm Vertical](https://www.flux.ai/vasy_skral/pin-header-01x06-254mm-vertical~jyw.md) - License: https://creativecommons.org/licenses/by/4.0/ - Role Details: Test point access - Role: Connector - Part Type: Connector **Pins:** - Pin_1 [pin 1] - Pin_2 [pin 2] - Pin_3 [pin 3] - Pin_4 [pin 4] - Pin_5 [pin 5] - Pin_6 [pin 6] ### TP2 — [Pin Header 01x02 2.54mm Vertical](https://www.flux.ai/jharwinbarrozo/generic-pin-header-01x02-2p54mm-vertical~4uy.md) - Role: Connector - Package: 1x02 2.54mm - License: https://creativecommons.org/licenses/by/4.0/ - Part Type: Connector - Role Details: Test point for ADC channel A input net **Pins:** - P1 [pin 1] - P2 [pin 2] ### TP2 — [Pin Header 01x02 2.54mm Vertical](https://www.flux.ai/jharwinbarrozo/generic-pin-header-01x02-2p54mm-vertical~4uy.md) - Role Details: Test point for ADC channel A input net - License: https://creativecommons.org/licenses/by/4.0/ - Part Type: Connector - Role: Connector **Pins:** - P1 [pin 1] - P2 [pin 2] ### TP3 — [Pin Header 01x02 2.54mm Vertical](https://www.flux.ai/jharwinbarrozo/generic-pin-header-01x02-2p54mm-vertical~4uy.md) - Role Details: Test point for ADC channel B input net - Role: Connector - Part Type: Connector - License: https://creativecommons.org/licenses/by/4.0/ - Package: 1x02 2.54mm **Pins:** - P1 [pin 1] - P2 [pin 2] ### TP3 — [Pin Header 01x02 2.54mm Vertical](https://www.flux.ai/jharwinbarrozo/generic-pin-header-01x02-2p54mm-vertical~4uy.md) - License: https://creativecommons.org/licenses/by/4.0/ - Part Type: Connector - Role Details: Test point for ADC channel B input net - Role: Connector **Pins:** - P1 [pin 1] - P2 [pin 2] ### U1 — [OPA1602AID](https://www.flux.ai/jecstronic/opa1602aid~jnr.md) - Role Details: Dual mic preamp op amp (two channels) - Part Type: Operational Amplifier (OP-AMP) - Package or Case Code: 8-SOIC - Integrated Circuit Type: Linear - Operating Voltage: 12V - Manufacturer Name: Texas Instruments - Package: SOIC-8_3.9x4.9mm_P1.27mm - Datasheet URL: https://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=https%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Fopa1602 - Role: Amplification - Manufacturer Part Number: OPA1602AID - Mount: Surface Mount **Pins:** - -IN A [pin 2] - -IN B [pin 6] - +IN A [pin 3] - +IN B [pin 5] - OUT A [pin 1] - OUT B [pin 7] - V- [pin 4] - V+ [pin 8] ### U2 — [OPA333AIDBVR](https://www.flux.ai/jecstronic/opa333aidbvr~7a.md) - Part Type: Operational Amplifier (OP-AMP) - Manufacturer Name: Texas Instruments - Role Details: 1.65 V mid-rail buffer - Datasheet URL: https://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=https%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Fopa333 - Integrated Circuit Type: Linear - Manufacturer Part Number: OPA333AIDBVR - Operating Voltage: 3.3V - Package or Case Code: SOT-23-5 - Package: SOT-23-5_L2.9-W1.6-P0.95-LS2.8-BR - Role: Voltage Reference Buffer - Mount: Surface Mount **Pins:** - - [pin 4] - + [pin 3] - OUTPUT [pin 1] - V- [pin 2] - V+ [pin 5] ### U4 — [OPA1602AID](https://www.flux.ai/jecstronic/opa1602aid~jnr.md) - Part Type: Operational Amplifier (OP-AMP) - Role: Buffering - Manufacturer Name: Texas Instruments - Datasheet URL: https://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=https%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Fopa1602 - Operating Voltage: 12V - Manufacturer Part Number: OPA1602AID - Role Details: Instrument input buffer (12 V) - Package: SOIC-8_3.9x4.9mm_P1.27mm **Pins:** - -IN A [pin 2] - -IN B [pin 6] - +IN A [pin 3] - +IN B [pin 5] - OUT A [pin 1] - OUT B [pin 7] - V- [pin 4] - V+ [pin 8] ### U5 — [OPA188AIDBVR](https://www.flux.ai/jecstronic/opa188aidbvr~4yk.md) - Manufacturer Part Number: OPA188AIDBVR - Mount: Surface Mount - Operating Voltage: 3.3V - Part Type: Operational Amplifier (OP-AMP) - Role Details: Buffer for 1.65 V reference - Datasheet URL: https://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=https%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Fopa188 - Role: Voltage Reference Buffer - Package: SOT-23-5 - Package or Case Code: SOT-23-5 - Manufacturer Name: Texas Instruments - Integrated Circuit Type: Linear **Pins:** - - [pin 4] - + [pin 3] - OUTPUT [pin 1] - V- [pin 2] - V+ [pin 5] ### U6 — [WE-TVS-82400102](https://www.flux.ai/kicad-part-library/we-tvs-82400102~vb9.md) - Datasheet URL: https://www.we-online.com/components/products/datasheet/82400102.pdf - Role: Protection - Package or Case Code: SOT-23-6 - Manufacturer Part Number: WE-TVS-82400102 - Role Details: TVS protection for MCU ADC input net - Manufacturer Name: Texas Instruments Inc. - Package: SOT-23-6 **Pins:** - ~ [pin 1] - ~ [pin 3] - ~ [pin 4] - ~ [pin 5] - ~ [pin 6] - ~ [pin 2] ### U7 — [WE-TVS-82400102](https://www.flux.ai/kicad-part-library/we-tvs-82400102~vb9.md) - Manufacturer Name: Texas Instruments Inc. - Package or Case Code: SOT-23-6 - Role Details: TVS protection for MCU ADC input net - Package: SOT-23-6 - Role: Protection - Manufacturer Part Number: WE-TVS-82400102 - Datasheet URL: https://www.we-online.com/components/products/datasheet/82400102.pdf **Pins:** - ~ [pin 1] - ~ [pin 3] - ~ [pin 4] - ~ [pin 5] - ~ [pin 6] - ~ [pin 2] ### VR1 — [PRM162-K420K-103B1](https://www.flux.ai/adrian95/prm162-k420k-103b1~pzx.md) - Role: Variable Resistor - Datasheet URL: https://www.bourns.com/docs/Product-Datasheets/PRM16.pdf - License: https://creativecommons.org/licenses/by/4.0/ - Part Type: Variable Resistor - Manufacturer Name: Bourns Inc. - Role Details: Preamp continuous gain control - Resistor Type: Potentiometer - Package: Panel mount - Mount: Through Hole - Package or Case Code: RES-ADJ-TH - Manufacturer Part Number: PRM162-K420K-103B1 **Pins:** - CCW_1 [pin 1] - CCW_2 [pin 4] - CW_1 [pin 3] - CW_2 [pin 6] - MH1 [pin MH1] - MH2 [pin MH2] - WIPER_1 [pin 2] - WIPER_2 [pin 5] ### VR2 — [PRM162-K420K-103B1](https://www.flux.ai/adrian95/prm162-k420k-103b1~pzx.md) - Manufacturer Name: Bourns Inc. - Part Type: Variable Resistor - License: https://creativecommons.org/licenses/by/4.0/ - Role: Variable Resistor - Datasheet URL: https://www.bourns.com/docs/Product-Datasheets/PRM16.pdf - Package: Panel mount - Resistor Type: Potentiometer - Manufacturer Part Number: PRM162-K420K-103B1 - Mount: Through Hole - Package or Case Code: RES-ADJ-TH - Role Details: Stereo master volume control **Pins:** - CCW_1 [pin 1] - CCW_2 [pin 4] - CW_1 [pin 3] - CW_2 [pin 6] - MH1 [pin MH1] - MH2 [pin MH2] - WIPER_1 [pin 2] - WIPER_2 [pin 5] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/alecdvor/audio-input-for-3p3v-adc~9v](https://www.flux.ai/alecdvor/audio-input-for-3p3v-adc~9v).* --- *Generated from [https://www.flux.ai/alecdvor/audio-input-for-3p3v-adc~9v](https://www.flux.ai/alecdvor/audio-input-for-3p3v-adc~9v)*