Phantom Powered Microphone Preamplifier – Low Noise – Professional Quality

  • Rajkumar Sharma
  • 523 Views
  • moderate
  • Tested
  • SKU: EL129554
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The project presented here is a professional quality Phantom powered Microphone pre-amplifier. The project is built using the INA163 chip from TI. The Chip is a very low-noise, low-distortion, monolithic instrumentation amplifier. R2 and R3 provide a current path for a conventional 48V phantom power source for a remotely located microphone. A slide switch SW1 allows phantom power to be disabled. C6 and C8 block the phantom power voltage from the INA163 input circuitry. Additional input protection against ESD and hot-plugging, four 1N4148 diodes D1, D2, D3, D4 connected from the input to supply lines. R7 and R8 provide a path for the input bias current of the INA163. Gain is set with a variable resistor, PR1, in series with R4. R4 determines the maximum gain. The total resistance, R4 + PR1, determines the lowest gain. A special reverse-log taper potentiometer for PR1 can be used to create a linear change (in dB) with rotation. LED D5 is used as a power indicator. L1, L2, C7, C10, and C11 components protect the inputs from EMI and RFI noise.

Optional DC Output Control Loop

Input offset current (typically 100nA) creates a DC differential input voltage that will produce an output offset voltage. This is generally the dominant source of the output offset voltage. With a maximum gain of 1000 (60dB), the output offset voltage can be several volts. This may be entirely acceptable if the output is AC-coupled into the subsequent stage. An optional circuit is provided to tackle this problem. An inexpensive FET-input op-amp U2A in a feedback loop drives the DC output voltage to 0V. Op-Amp is not in the audio signal path and does not affect signal quality.

Install the Following Components for DC Output Control Loop

  • U2A = OPA2134 SOIC8
  • C9 = Ceramic Capacitor 0.1uf/50V SMD Size 0805
  • R6 1Mega Ohm 5% SMD Resistor Size 0805
  • Omit Resistor R5

Connections and Other Details

  • CN1: Pin 1 = +48V DC Phantom Power Input, Pin 2= GND
  • CN2: Pin 1-2 = VCC +15V DC, Pin 2-3 = GND, Pin 4-5 VEE -15V DC
  • CN3: Pin 1 = BB Microphone – VIN, Pin 2 = GND, Pin 3 = AB Microphone + VIN
  • CN4: Pin 1 = Audio Output, Pin 2 = GND
  • D5: Power LED
  • SW1: Phantom Power Enable/Disable Switch
Note: Non-polarized capacitors should be used for C1 and C2 if phantom power is to be disabled.

Features

  • Power Supply Dual 15V DC (+/-15V DC)
  • On Board Power LED
  • Slide switch for Phantom Power Enable/Disable
  • 3 Pin Screw Terminal for Microphone Connections
  • 2 Pin Screw Terminal for Audio Output
  • 2 Pin Screw Terminal for Phantom Power Input 48V DC
  • 6 Pin Male Header for Power Input
  • Gain Up to 1000/V (60dB)
  • Potentiometer PR1 Gain Adjust
  • PCB Dimensions 60.17 x 39.85mm
  • 4 x 3mm Mounting Holes

Schematic

Parts List

NO.QNTY.REF.DESC.MANUFACTURERSUPPLIERPART NO
11CN12 PIN SCREW TERMINAL PITCH 5.08MMPHOENIXDIGIKEY277-1247-ND
21CN26 PIN MALE HEADER PITCH 2.54MMWURTHDIGIKEY732-5319-ND
31CN33 PIN SCREW TERMINAL PITCH 5.08MMPHOENIXDIGIKEY277-1248-ND
41CN42 PIN SCREW TERMINAL PITCH 5.08MMPHOENIXDIGIKEY277-1247-ND
53C1,C6,C847uF/63V ELECTROLYTIC OR READ NOTE 6.3MM OR 8MMCORNEL DUBILIERDIGIKEY1572-1736-ND
62C2,C40.1uF/50V CERAMIC SMD SIZE 0805MUARATA/YAGEODIGIKEY
72C3,C5220uF/25V ELECTROLYTIC 8MM/13MMRUBYCONDIGIKEY1189-3720-1-ND
83C7,C10,C11470PF/63V CERAMIC SMD SIZE 0805MUARATA/YAGEODIGIKEY
93U2,R6,C9DNP/OPTIONAL
104D1,D2,D3,D41N4148 SMD MICROCHIPDIGIKEY1086-15206-ND
111D5LED RED SMD SIZE 0805OSRAMDIGIKEY475-1278-1-ND
122L1,L2FERRITE BEAD SMD SIZE 0805LAIRDDIGIKEY240-2394-1-ND
131PR11K POTENTIOMETER 17MM LOGADAFRUITDIGIKEY1528-5265-ND
141R147K 5% SMD SIZE 0805MUARATA/YAGEODIGIKEY
152R2,R36K8 1% SMD SIZE 1206MUARATA/YAGEODIGIKEY
161R45E 1% SMD SIZE 0805MUARATA/YAGEODIGIKEY
171R50E SMD SIZE 0805MUARATA/YAGEODIGIKEY
183R7,R8,R92K2 5% SMD SIZE 0805MUARATA/YAGEODIGIKEY
191SW1SLIDE SWE-SWITCHDIGIKEYEG1916-ND
201U1INA163 SOIC14TIDIGIKEYINA163UA-ND

Connections

Gerber View

Photos

Video


Datasheet

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