Mercury 66-IV is a single-channel all-tube limiter built on the variable-bias circuit known from the Fairchild 660 — a compressor that remains the reference point in its class. Inputs and outputs are transformer-balanced.
Compression you do not hear as compression
A variable-mu circuit changes tube gain through the bias voltage rather than through a separate control element in the audio path. The time constant moves with the signal, so reduction has no rigid threshold and leaves none of the characteristic pumping. On vocals and on a bus you can even out several decibels of dynamics and hear the result rather than the device working.
Every stage tube, with no shortcuts
This is a fully tube design, not a hybrid — including the control and output stages. In practice that means more colour than mixed topologies and different behaviour when driven hard, where the path starts to thicken rather than harden.
KEY FEATURES
- Single-channel all-tube limiter
- Variable-bias circuit in Fairchild 660 topology
- Transformer-balanced input and output
- Program-dependent time constants
- Works on individual tracks and on the bus
- Designed and built by Mercury Recording Equipment
TECHNICAL SPECIFICATIONS
- Type: tube limiter, variable-bias circuit
- Channels: 1
- Reference circuit: Fairchild 660
- Inputs and outputs: balanced, transformer-coupled
- Construction: all-tube
