DOEPFER / A-171-4 Quad VC Slew Limiter

Variations

The A-171-4 Quad VC Slew Limiter is a voltage controlled slew limiter with four identical units. Its primary purpose is to provide portamento functionality for each note of a chord, but it can also be used for other applications where multiple through-limiters are required.

The common slew time is manually adjustable and can be further controlled by an external voltage. This module uses a photosensitive resistor (LDR). Therefore, due to errors in the LDR and the LEDs that illuminate it, the slew time will not be exactly the same for all units. The input and output of the slew limiter are buffered to avoid voltage drop. This is especially important for use in creating portamento effects in polyphonic synths. This means that each output can drive multiple VCOs without the need for external buffers. In addition, the inputs and outputs of the through-limiters can use pin-header wiring as a pre-internal wiring for the polyphonic series. The signal from this internal wiring can be removed by patching it to a jack on the front panel.

Controls
Man.: manual control of the slew limiter value (base value)
CV: signal attenuator applied to the CV socket
Input and output
CV: control voltage input
Input jacks 1~4: input of slew limiter signal
Output jacks 1~4: output of slew limiter signal
LED: slew limiter time Visual indication (dark = long time, bright = short time)
Technical note:
Each photosensitive resistor (LDR), together with its associated capacitor, forms a simple RC circuit connection. Each input and output is buffered.
The slew time range is approximately 5 ms ... 10 s (1:2000). Due to LDR and LED tolerances, the slew time may vary slightly from unit to unit. This range can be changed by changing the capacitor value. A smaller capacitor value allows the slew limiter to be used as a 6dB low-pass filter. Increasing the capacitor value increases the slew time. (*Replacement of the capacitor is a modification and is not covered by our support.)
Four photosensitive resistors (LDRs) and LEDs are integrated in a small light-shielding box. In addition, the printed circuit board is made of light-shielding black material to avoid light interference from other modules and bus boards.
Two pin headers with four pins each are available on the module's printed circuit board. These are provided for the internal wiring of the polyphonic module.
In 1~4: The pins of this pin header are connected to the switch contacts of input jacks 1~4. This allows for internal connections to the CV output of the polyphonic MIDI to CV module A-190-5. An internal connection to the A-190-5 is established unless sockets 1...4 are used.
Out 1~4: The pins of this pin header are connected to the outputs Out 1~4. This provides an internal 4-wire connection to the CV inputs of the polyphonic VCO A-111-4.

The following document shows the location and function of the module jumpers and trimming potentiometers: A171_4_trimming_potentiometers_and_jumpers.pdf

Please note that failure of adjustment by the customer or malfunction due to this will not be covered by the warranty.

Width 4HP
Depth 45mm
Current consumption
+12V : 40mA
-12V : 40mA