2 layers74 × 48 mm Mic amp, the printed circuit board in 3D

Mic amp

Microphone amplifier for Knowles Electret microphones

Size: 74 × 48 mm
Copper layers: 2
Thickness: 1.6 mm
Parts: 32
Nets: 15
Pads: 74
Tracks, vias: 102, 0
Pours: 1
Routed: Yes
KiCad: KiCad 4
Created: 19 Dec 2017
Updated: 6 Feb 2018

Overview

Mic amp is an open-source printed circuit board by bburan, from the bburan/mic-amp repository on GitHub. It is a 2-layer board of 74 × 48 mm with 32 parts on 15 nets, routed with 102 tracks and 0 vias.

It is built around the LM317. Its parts include 11 capacitors, 10 connectors, 8 resistors and 2 ICs. It belongs with the audio and music boards of this library.

Main components

LM317
SOT-223-40℃~+85℃@(Ta) 0.003%Vout 1 1.3V~37V 1A 40V 80dB@(120Hz) Adjustable Positive Short Circuit Protection、Thermal shutdown SOT-223 Voltage Regulators - Linear, Low Drop Out (LDO) Regulators ROHSJSMSEMIVoltage Regulators - Linear, Low Drop Out (LDO) Regulators

README

README.md

Microphone amplifier for Knowles Electret microphones

Overview

This printed circuit board (PCB) is based on the design created at Eaton Peabody Laboratories (Mass. Eye and Ear Infirmary), but redesigned to work at lower frequencies. It features:

High-pass input filter with 96 Hz cutoff.
Selectable 20 or 40 dB gain
Low-pass amplification with a 72 kHz cutoff.
Low-noise 1.5V supply for microphone with a low-pass filter cutoff of 0.33 Hz (ensuring that very little noise makes it into the microphone).

Rendering of PCB

The board is 74mm x 48mm and the mounting holes, spaced 40mm x 40mm, are sized for a M3 screw. The board will fit in a Hammond enclosure that accomodates 75mm wide boards.

Getting started

OSH Park will print and ship three of these boards for approximately $30.

Order the parts from the bill of materials.

Solder the parts using solder with water-soluble flux.

Wash the board with dH₂O.

Parts

Qty	Value	Footprint	References
5	0.1uF	custom:C_Rect_L4.0mm_W3.5mm_P2.50mm	C5, C12, C13, C22, C23
4	CONN_01X01	MountingHole:MountingHole_3.2mm_M3	J4, J5, J6, J7
3	CONN_01X02	Conn_PinSocket_2.54mm:PinSocket_1x02_P2.54mm_Vertical	J1, J8, J10
2	100	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R10, R11
2	100uF	Capacitor_THT:CP_Radial_D10.0mm_P5.00mm	C6, C7
2	10k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R13, R31
2	1uF	custom:C_Rect_L5.5mm_W4.0mm_P2.50mm	C10, C11
2	CONN_01X03	Conn_PinSocket_2.54mm:PinSocket_1x03_P2.54mm_Vertical	J3, J9
1	220pF film	Capacitor_THT:C_Rect_L7.2mm_W4.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2	C31
1	33nF film	Capacitor_THT:C_Rect_L7.2mm_W8.5mm_P5.00mm_FKP2_FKP2_MKS2_MKP2	C1
1	4.7K	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R24
1	475	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R22
1	49.9k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R1
1	90.9	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R23
1	CONN_01X01	Conn_PinSocket_2.54mm:PinSocket_1x01_P2.54mm_Vertical	J2
1	LF356	Package_DIP:DIP-8_W7.62mm_LongPads	U2
1	LM317	Package_TO_SOT_THT:TO-92_Inline_Wide	VREG1
1	LME49710	Package_DIP:DIP-8_W7.62mm_LongPads	U1

Questions

How big is the Mic amp PCB?

It measures 74 × 48 mm and has 2 copper layers, 1.6 mm thick.

What parts does the Mic amp use?

32 parts, built around the LM317. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.

Where can I download the Mic amp KiCad files?

From the bburan/mic-amp repository on GitHub, at the commit this page was made from: the board is mic amp.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.

Can I use the Mic amp design in my own project?

Its repository states no licence, so its author keeps all rights: ask bburan before reusing the design.

Category and platform

Audio and music

Topics

circuit pcb kicad knowles-electret-microphones microphone-amplifier microphone

Project files

Show this board on your page

A live frame, for any web page

<iframe src="https://pcbkit.io/embed/boards/bburan-mic-amp" title="Mic amp in PCBKit" width="100%" height="480" style="border:0;border-radius:12px" allow="fullscreen" loading="lazy"></iframe>

A picture

<img src="https://pcbkit.io/embed/boards/bburan-mic-amp.jpg" alt="Mic amp" width="1200" height="900">

A picture that opens the board, for a README

[![Mic amp](https://pcbkit.io/embed/boards/bburan-mic-amp.jpg?size=s)](https://pcbkit.io/boards/bburan-mic-amp)

Source

Repository: bburan/mic-amp
Board file: mic amp.kicad_pcb
Commit: 638977d
Licence: Not stated

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