{"id":22419488,"url":"https://github.com/dunkelstern/electret_preamp","last_synced_at":"2025-04-13T13:41:30.396Z","repository":{"id":142590498,"uuid":"268181300","full_name":"dunkelstern/electret_preamp","owner":"dunkelstern","description":"Electret Microphone Preamp based on Texas Instruments Single-Supply, Electret Microphone Pre-Amplifier Reference Design by John Caldwell","archived":false,"fork":false,"pushed_at":"2020-06-02T10:20:34.000Z","size":6591,"stargazers_count":5,"open_issues_count":0,"forks_count":3,"subscribers_count":2,"default_branch":"master","last_synced_at":"2025-03-27T04:41:34.633Z","etag":null,"topics":["electret","jupyter-notebook","kicad","microphone","pcb-layout","preamp","schematic"],"latest_commit_sha":null,"homepage":null,"language":"Jupyter Notebook","has_issues":true,"has_wiki":null,"has_pages":null,"mirror_url":null,"source_name":null,"license":null,"status":null,"scm":"git","pull_requests_enabled":true,"icon_url":"https://github.com/dunkelstern.png","metadata":{"files":{"readme":"Readme.md","changelog":null,"contributing":null,"funding":null,"license":null,"code_of_conduct":null,"threat_model":null,"audit":null,"citation":null,"codeowners":null,"security":null,"support":null,"governance":null,"roadmap":null,"authors":null,"dei":null,"publiccode":null,"codemeta":null}},"created_at":"2020-05-31T00:15:29.000Z","updated_at":"2025-03-11T10:47:24.000Z","dependencies_parsed_at":null,"dependency_job_id":"ccae78cc-7b70-4bec-875b-f41484fd5f97","html_url":"https://github.com/dunkelstern/electret_preamp","commit_stats":null,"previous_names":[],"tags_count":0,"template":false,"template_full_name":null,"repository_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dunkelstern%2Felectret_preamp","tags_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dunkelstern%2Felectret_preamp/tags","releases_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dunkelstern%2Felectret_preamp/releases","manifests_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/dunkelstern%2Felectret_preamp/manifests","owner_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners/dunkelstern","download_url":"https://codeload.github.com/dunkelstern/electret_preamp/tar.gz/refs/heads/master","host":{"name":"GitHub","url":"https://github.com","kind":"github","repositories_count":248724317,"owners_count":21151557,"icon_url":"https://github.com/github.png","version":null,"created_at":"2022-05-30T11:31:42.601Z","updated_at":"2022-07-04T15:15:14.044Z","host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":["electret","jupyter-notebook","kicad","microphone","pcb-layout","preamp","schematic"],"created_at":"2024-12-05T16:15:53.952Z","updated_at":"2025-04-13T13:41:30.382Z","avatar_url":"https://github.com/dunkelstern.png","language":"Jupyter Notebook","funding_links":[],"categories":[],"sub_categories":[],"readme":"# Electret Microphone Preamp\n\nThis design is purely based on [Texas Instruments Single-Supply, Electret Microphone Pre-Amplifier Reference Design by John Caldwell](http://www.ti.com/lit/ug/tidu765/tidu765.pdf?ts=1590780945605)\n\nThe Jupyter notebook is basically a interactive Version of that reference design PDF. I claim no copyright on this.\n\n## What you will find here\n\n### Jupyter Notebook\n\nThe included Jupyter Notebook is an interactive version of the reference design PDF from Texas instruments. You can\nplay with all values and let the program re-calculate all relevant values to be used in your own design.\n\nThere are some areas that will be most important:\n\n- Operating Voltage of the Preamp\n\n![Operating Voltage](img/intro_vcc.png)\n\n- Parameters of the Microphone capsule in use\n\n![Microphone parameters](img/intro_mic.png)\n\n- Acceptable high-frequency attenuation\n\n![Acceptable Attenuation at high frequencies](img/intro_attenuation.png)\n\n- Acceptable low-frequency cutoff in output highpass filter\n\n![Output capacity](img/intro_highpass.png)\n\n- The List of passive component values\n\n![Passives](img/intro_passives.png)\n\n- The Op-Amp parameters to look out for\n\n![Op-Amp Parameters](img/intro_opamp.png)\n\n### LT Spice simulation\n\nI have simulated the circuit in LTSpice with some different Op-Amps I had in stock.\nI deviated from the `270k` resistor in the Op-Amp feedback loop and opted for a `180k` value. This\nmeans the amplification of the Op-Amp will not reach `0dB` (max. seems to be around `-1.8dB`) but the circuit seems\nto run more stable at that amplification.\n\nHere are some bode-plots of the frequency response for some tested Op-Amps:\n\n#### OP07\n\n![Bode plot for OP07](img/bode_plot_op07.png)\n\nThe OP07 is the worst possible of the bunch. The bad response is a product of the sub-optimal slew rate of ![0.3V per uS](https://render.githubusercontent.com/render/math?math=0.3%5Cfrac%7BV%7D%7B%5Cmu%20S%7D).\nAdditionally this Op-Amp will add noise to the signal as it's input voltage noise is around ![10](https://render.githubusercontent.com/render/math?math=10\\frac{nV}{\\sqrt{Hz}}). Ideally\nit should be below ![6.6](https://render.githubusercontent.com/render/math?math=6.6\\frac{nV}{\\sqrt{Hz}}) as we can see in the calulations.\n\n#### TL072\n\n![Bode plot for TL072](img/bode_plot_tl072.png)\n\nThe TL072 is a bit better than the OP07. The slew rate of ![16V/uS](https://render.githubusercontent.com/render/math?math=16%5Cfrac%7BV%7D%7B%5Cmu%20S%7D) is at least enough.\nThis Op-Amp will add a lot of noise to the signal as it's input voltage noise is around ![15](https://render.githubusercontent.com/render/math?math=15\\frac{nV}{\\sqrt{Hz}}). Ideally\nit should be below ![6.6](https://render.githubusercontent.com/render/math?math=6.6\\frac{nV}{\\sqrt{Hz}}) as we can see in the calulations.\n\n#### NE5532\n\n![Bode plot for NE5532](img/bode_plot_ne5532.png)\n\nThe NE5532 is really good at this. All parameters are within the parameter range we calculated.\n\n#### LM318\n\n![Bode plot for LM318](img/bode_plot_lm318.png)\n\nYou can see why the LM318 is used for these applications a lot, as it is a dedicated Audio-Op-Amp the response from\nthis thing is the best of the bunch.\n\n**Attention**: The `LM318` needed `5.3V` operating voltage to actually do anything in the simulation, I have not\nverified if this is an artifact of the simulation or an actual problem!\n\n### KiCAD design\n\nThe KiCAD design is based on surface mount components to save as much space as possible. You could use tantalum\ncapacitors instead of the electrolyte I used here, but they are expensive and I don't have them in stock.\n\n![KiCAD schematic](img/schematic.png)\n\nThe board design is optimized for space and to be single sided as it is easier to prototype this way.\nI will probably add a better two sided design in the future which will be optimized for noise performance and\nwill probably get even smaller (but I have to order the PCBs then)\n\n![KiCAD board layout](img/board_layout.png)\n\nThis is what the board looks like rendered, I will add a photo of the finished product when I have built one.\n\n![KiCAD board render](img/board_render.png)\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdunkelstern%2Felectret_preamp","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fdunkelstern%2Felectret_preamp","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdunkelstern%2Felectret_preamp/lists"}