IntermediateAudio & Test Equipment
LM358 Buffered Low-Pass Filter
Filter high-frequency noise with a one-pole RC network and buffer the result so a following stage does not load it.
Parts from the database
- LM358P × 1Unity-gain buffer
Other supplies
- breadboardCommon build supply
- 5 V supplyCommon build supply
- 10 kΩ resistorCommon build supply
- 100 nF capacitorCommon build supply
- 100 nF bypassCommon build supply
- 0–2.5 V signal sourceCommon build supply
- oscilloscope or multimeterCommon build supply
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Connections
- Power DIP-8 pin 8 from +5 V and pin 4 from ground; bypass.
- Signal through 10 kΩ to filter node; 100 nF from node to ground. Cutoff is 1/(2πRC), about 159 Hz.
- Connect node to amplifier A pin 3. Connect output pin 1 to inverting input pin 2 for a follower.
- Tie unused amplifier B as a follower at ground. Keep signal in the 0–2.5 V range.
Build steps
- Measure the RC node before adding the op amp.
- Apply slow voltage and verify output follows it.
- Apply a square wave; high-frequency edges should round while slow changes remain.
- Change capacitor and predict the cutoff before re-measuring.
Software and firmware setup
This is a hardware-only circuit; no firmware is required.
Test your build
The buffer follows the RC node; 10 kΩ with 100 nF gives a single-pole cutoff near 159 Hz.
Troubleshooting
- Clips near positive rail: reduce input range.
- No filtering: put capacitor from RC node to ground and resistor in series with source.
- Noisy output: shorten feedback wiring and add bypass.
Safety and limitations
Low-voltage signals only; never connect an unknown or mains-referenced source to the breadboard.
Manufacturer and platform documentation
Community Notes for This Project
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