Doepfer A-171-2

The A-171-2 is based on the CGS75 from Ken Stone which is itself a licensed adaptation of the Serge DTG/DUSG and is licensed from both therefore the higher price in comparison to other Doepfer modules. As a multitool it can be used for various tasks apart from the obvious slew generation: LFO, Envelope Generator, Low-Pass-Gate, Envelope Follower, VC Pulse Delay, Sub-Harmonic Generator or Oscillator (not recommended for playing notes though as the tracking is not exactly 1V/Oct).
Apart from the exp/lin switch the curve can also be set with the CV pots when nothing is patched in their input jackets. It then works similar to the log/lin/exp pot of the Maths from Make Noise which is very handy for setting subtle responce characteristics.
Beware that in the standard configuration it outputs only +5V which you can set with a trimmer. So modules needing more juice might sound different or filters might not completely open. E.g. this is important when combining the module with Make Noise or Malekko modules. In this case set the trimmer appropriately or use an external amplifier (a real amplifier as most VCAs are just attenuators).
I also own a Maths but prefer the A-171-2 as an Envelope Generator because in my opinion it sounds better with more snap. Might be because I'm using Doepfer VCAs (A-131-3 with the CEM3360). It's also easier to use attenuated CV on the A-171-2 because you have to patch another channel (2 or 3) of the Maths (or Function) to get CV attenuation and as the cycle swith is a mechanical switch it's state doesn't reset when powering down the modular.

When one thinks of a slew processor, one tends to think of notes sliding. Don't be fooled by the name; this module is capable of much more interesting tricks than that. CV control of lin / exp response is quite interesting, as is the ability to either slew an incoming signal or trigger an envelope from the A-171-2. When you flip the "cycle" switch on, it becomes a kind of VCLFO that will create sine to spiky waveforms with CV control of rise and fall.

At its most aggressive settings, it creates envelopes that are perfect for kick drums or other percussive hits. This module is a bit of a swiss army knife, as most of Serge's designs are.