FMR Audio PBC-6A (Really nice mono compressor)

The PCB-6A is a mono compressor which is described as being pretty agressive. Note that besides the classic Attack, Release and Output knobs, it features an adjustable Knee and a Drive circuit.

Features

• No Threshold
  There’s no threshold in the PBC-6A. Unlike compressors with
  threshold controls, the signal passing through the PBC-6A is always being compressed
  rather than compressing only those parts of the signal that are above a set
  threshold. This makes the PBC-6A a non-linear, compression amplifier (CA).

• Level Dependent Ratio
  The PBC uses a feedback configuration to help
  achieve its function. Along with this, the PBC’s detector allows higher output signals
  to compress more than lower-level ones. With the lack of thresholding, the
  change in ratio is smooth and gradual from low-level signals to higher-level.

• Knee Control
  This allows a transition from lower-to-higher ratios to occur
  over a smaller range than would “naturally” happen due to the PBC’s feedback
  and detector configuration.
  These main features help the PBC-6A achieve a wide-range of compression effects—from delicate to
  crushed!

Specifications