DoepferA-121s Stereo Multimode Filter

Doepfer A-121s

Doepfer's A-121s is a two-pole multimode stereo filter with independent and linked control options for each filter, letting you widen the stereo field, self-patch for series, or use it as two separate filters. A large knob controls the frequency cutoff for both filters and two additional smaller controls are available for individual frequency adjustment of each filter. The resonance situation is similar: a main Q knob controls how much for both and beneath it, two smaller controls for the individual resonance amount. Each filter can have their mode individually set or linked together, able to smoothly morph from low pass–notch–high pass–band pass. A Delta (∆) control lets you adjust the spread of the two frequencies which is great for widening your mix or creating interesting sonic timbres. With CV control over all parameters, the Doepfer A-121s Stereo Multimode Filter is a versatile addition to any rack.

A-121s Features

• 12dB/oct Stereo Multimode Filter
• Runs as a stereo filter, parallel dual mono filter, or in series by self-patching
• Morph each filter individually between LP–N–HP–BP or link them for stereo operation
• Frequency spread control (∆) with FM input
• Smaller control knobs are attenuverters/polarizers (neutral is at 12 o'clock)
• In1 normalized to In2
• Internal jumper changes the behavior of QM controls to modulate the filter type
• Individual attenuators for inputs