Umbra

Stereo Feedback Accumulator

Umbra is a dual channel feedback processor with three discrete transistor core VCA pairs. Route any eurorack-level effects, compressors or filters through its send/return paths to create feedback loops ranging from subtle textured echoes to howling walls of sound. The input level VCA is positioned before the feedback circuit, allowing time based sounds to fade naturally when the VCA is closed. A soft clipping stage after all feedback keeps levels controlled while adding nonlinearities and character. The left-right channel normalling allows for both mono-to-stereo or true stereo operation.

Features

• Discrete transistor core VCAs for input gain (L and R), VCA pair for return gain, and VCA pair for feedback amount.
• Switchable between stereo operation and serial mono operation, where the output of the left channel enters the input on the right channel, doubling up on feedback and processing, indicated by the color of the LEDs. Orange L and R channels = Stereo operation, Orange L channel, Blue R channel = Serial operation
• Asymmetric diode soft clipping distortion at output.
• Level LEDs for input level and return level, to keep feedback, drive and gain under control.

Controls

• IMBUE: Input Level knob (controls both channels)
• FEED: Feedback amount knob (controls both channels)
• DRAIN: Return level knob (controls both channels)
• Parallel or serial operation switch

Technical Specifications

• Width: 10HP

Patch Ideas

1. Two-Stage Serial Processing: Leave channel 2's input jack unplugged to create two stages of cascading feedback effects. The first channel's output feeds directly into the second channel's processing chain, creating complex, distorted and evolving textures with each stage having its own return effects.
2. Mono to Stereo Expansion: Use a mono source and let the normalling split it to both channels, making the signal stereo.
3. Stereo Reverb Loops: Process stereo reverb through the feedback path to build immersive spaces. Use CV modulation on the feedback for evolving textures.
4. Dual Mono Processing: Use each channel independently with different effects for parallel feedback experiments, unified by the shared controls.

Uses

• Adding a filter, filter bank, delay, reverb, waveshaper, or any other effect into the feedback loop.
• Heavy soft clipping distortion.
• No input feedback mixing.
• 3 stage VCA with distortion

Included

• Umbra module
• Power cable