RIVER main Passive 2-Channel Line Merger

The Palmer Main is a professional passive stereo merge box designed to solve common live sound and installation challenges. Sometimes two stereo sources — such as mixing consoles feeding a stereo power amplifier — need to be combined into a single input. This often causes ground loop problems, but the Palmer Main provides a clean and reliable solution.
Using a resistor matrix, the Main safely mixes two stereo input signals, while input pair A is galvanically isolated by a transformer to eliminate hum and ground noise. Thanks to its passive operation, it requires no power supply, ensuring absolute reliability and a very low noise floor.
Equipped with large high-quality transformers, the Palmer Main can handle signals up to +20 dBu without distortion. Even when input A is unbalanced, the output remains fully balanced, guaranteeing professional-level signal integrity.
Housed in a rugged aluminium/steel chassis with XLR connectors, the Palmer Main is built to withstand the demands of stage, touring, and installation environments.
Key Features

Passive stereo merge box — no power required

Safely mixes two stereo signals into one output

Input pair A is transformer-isolated to eliminate ground loops

Handles high signal levels up to +20 dBu without distortion

Output remains balanced, even with unbalanced inputs

Rugged aluminium/steel housing for stage reliability

Professional XLR connectors for secure connections

Neutral sound with ultra-low noise floor

Specifications

Model: Palmer Main

Type: Passive stereo merge box

Inputs: 2 × stereo pairs (XLR)

Outputs: 1 × stereo pair (XLR, balanced)

Input isolation: Pair A transformer-isolated

Max input level: +20 dBu

Power: Passive (no power required)

Housing: Aluminium/steel chassis

Applications: Live sound, installations, mixing, signal routing