Slew Limiter

A slew limiter is a simple circuit that makes changes in voltage more gradual. This build has independent rise and fall settings. Rise controls how fast a voltage ramps up, while fall controls fast a voltage can drop down.

Both rise and fall at maximum

I use it with a sequencer to make my oscillators slide up or down to notes. You can also use it with a gate source as a simple AR envelope generator. The circuit will even work as a low pass filter!

My Slew Limiter build from the front

This build is based on HAGIWO’s Slew Limiter.

He has a more in-depth discussion about this build on his website (Tip: Google Translate works great!). He also has a nice demo of it on his Youtube channel.

Build

I built this circuit as a deadbug module. Due to the minimal parts count, I think this is a good point-to-point building exercise.

Deadbug circuitry for my Slew Limiter

The front panel I use is 3D-printed. I designed it using my EuroPanelMaker library for OpenSCAD. You can find my STL and OpenSCAD files on Github.

Front panel for the Slew Limter on OpenSCAD

I power it using a 3-pin JST XH2.54 connector with +12V, GND, and -12V. It is supplied by a custom-made bus board that I use for most of my Eurorack stuff.

Schematics

I got my initial schematics for this from HAGIWO’s design.

I flipped the pins of the potentiometers such that clockwise = more rise and fall times.

Schematics for my Slew Limiter

Testing

Here are some test outputs from my oscilloscope.

I have the input signal hooked up on channel 1 (yellow) and the output at channel 2 (blue). These tests were done with a 1uF capacitor at C1. The input signal I’m testing it with is from my Baby-8 sequencer clocked at 120BPM.

Both rise and fall at minimum

Rise at 12 o' clock

Fall at 12 o' clock

Both rise and fall at maximum

C1 can be swapped with higher/lower capacitors for longer or shorter rise and fall times.

My Slew Limiter's rise and fall controls

Conclusion

I’ve really enjoyed having this as an option on my modular rig. I’m thinking of doing a 2HP PCB for it – I really should be releasing more PCBs!

Huge thanks again to HAGIWO for making your designs open-source.

Follow me on Instagram @benjiaomodular for more updates.