Low pass filter

Low-Pass Filter

2024-08-23

• There's a failure mode where the output is silent and one of the resonance LEDs is solid on and the other is solid off. This seems to mean that the TL074 is damaged. It seems that this circuit damages the TL074 when certain pins are connected by accident. There's also a failure mode that damages the LM13700. Not sure what causes that.
• Next time don't bother including the high-pass filter. It complicates the circuit and UI, is not likely to be used, and doesn't work particularly well. Build a dedicated high-pass filter if necessary.
• The circuit has a bug where the volume of the self-oscillation signal drops quickly above a certain frequency. This has the effect of limiting the effect of resonance. This is only a bug in the final implementation of the filter; breadboard implementations of the design don't have this problem.
• The stripboard is slightly too large to comfortably fit in the case.
• Using a safety pin to group cables together and drilling a hole in the stripboard for cable management was effective at reducing the tangle of cables and made it easy to work on the circuit after starting work on the front panel.
• Build a subset of the circuit first. Use self-oscillation to test the circuit incrementally as it's built.

2024-08-25

• Rebuilt about half the circuit, intermittently testing against a breadboard implementation.
• One issue that came up was the cutoff potentiometer not responding sometimes. Reflowing its connection to the board seemed to fix the problem.