The A-171-4 Quad VC Slew Limiter from Doepfer is a quadruple voltage controlled portamento for polyphonic patches. Slew time is set for all four units together and has an effective range of 5 ms to 10 seconds. At the same time, the circuit evaluates the voltage change at each input separately. In addition, the inputs and outputs are buffered which counteracts voltage drop. The four units work with photo resistors, therefore minimal deviations in the control time result. The change in slew time can be modulated by a CV input with attenuator. Primarily A-171-4 is intended for polyphonic patches, but it is also suitable for monophonic patches and those that only need the same slew value.