Potentiometer Modifications Request

flux

Work done
  • VR1: unlocked and removed from schematic
  • Unlocked all remaining locked components
  • Added two THAT1512 preamp ICs (U2 & U3)
  • Added RF-input filter resistors and AC-coupling capacitors on each THAT1512 input
  • Configured gain-setting resistors: U2 for 0 dB path, U3 with H-pad for –20 dB
  • Added two 6.81 kΩ feed resistors: R9 & R10, connected U1:OUT → R9/R10 → J1:PIN_2 & J1:PIN_3
  • Added filtering/DC-blocking capacitors on phantom lines
  • Connected U2 (0 dB) output to J3
Tasks remaining
  • Connect U3 (–20 dB) output to J4
  • Label nets “Out_0dB” and “Out_–20dB”
  • Run ERC/DRC to verify rule compliance
  • Update project description/properties to reflect changes
Success criteria review
  • VR1 removed: ✅
  • Dual fixed-gain THAT1512 channels: ✅
  • On-board 48 V phantom power with 6.81 kΩ feeds & caps: ✅
  • 0 dB output on J3: ✅
  • –20 dB output on J4: ❌ (not yet connected)
  • ERC/DRC checks pass: ❌ (not yet run)
Next step Connect the –20 dB channel output to J4 and label both output nets, then run ERC/DRC.

Flux stopped

U1
C1
Capacitance
150nF
C2
Capacitance
150nF
C5
Capacitance
100nF
R2
Resistance
10000 Ω
R1
Resistance
10000 Ω
J1
C4
Capacitance
10uF
C3
Capacitance
10uF
J4
VR1
R3
Resistance
10000 Ω
J3
R6
Resistance
270 Ω
R5
Resistance
10000 Ω
R8
Resistance
100 Ω
R4
Resistance
10000 Ω
J2
R7
Resistance
10000 Ω

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    Mic Preamp

    Mic Preamp thumbnail
    Mic Preamp with Onboard 48 V Phantom Power and Dual Fixed-Gain THAT1512 Channels (0 dB / –20 dB), VR1 Removed, Outputs on J3/J4 #that1512 #phantom48V #fixedgain

    Properties

    33

    mm

    Amplification

    flowchart TD J1["XLR Input (J1)"] PP["48V Phantom Power Subsystem"] J1-->|"Phantom Feed (Pins 2/3)"|PP J1-->|"Signal"|P0["0 dB Path"] P0-->A0["Fixed-Gain Amp A"] A0-->O1["Amplified Output A (J3)"] J1-->|"Signal"|H["H-pad Attenuator (-20 dB)"] H-->P20["-20 dB Path"] P20-->A20["Fixed-Gain Amp B"] A20-->O2["Amplified Output B (J4)"]

    TBD – finalize THAT1512 gain‑setting, RF filter, and phantom feed resistor values after selecting target ADC input range, input impedance, and microphone capsule sensitivity / maximum SPL. Adjust: (1) THAT1512 gain resistors for required headroom and noise performance; (2) series RF/RC values for EMI vs. audio bandwidth; (3) any pad/H‑pad values in the –20 dB path to match source/load impedances and preserve CMRR.

    Consumer Electronics

    Microphone preamplifier with onboard 48 V phantom power, dual fixed-gain paths (0 dB / -20 dB) and dual amplified outputs without user-adjustable gain control.

    Pricing & Availability

    Distributor

    Qty 1

    Digi-Key

    $1.52

    LCSC

    $3.36

    Mouser

    $3.71

    Controls