54F50 Compressor / Limiter - API 500 series format
The 54F50 is a Class A, compressor and limiter module which occupies three slots in a 500 series rack. Fully populated with Carnhill transformers to achieve its distinctive classic sound. This high-end hand-built British module provides an affordable solution for the modern cost conscious studio.

Classic 4 stage (Class A) amplifier, 4 transformer design
All discrete component (no surface mount devices)
Entirely hand assembled and tested in the England to exacting quality standards.
Line Input: Carnhill transformer balanced (Mu-metal screened Classic VTB9046), 10k Input Impedance
Interstage: Carnhill Mu-metal screened Classic VTB9045 and VTB9046
Line Output: Carnhill transformer balanced (Classic full size output transformer)
Compressor: (Class A) amplifier design
o Ratio 1.5:1, 2:1, 3:1, 4:1 & 6:1
o Dual attack speeds (Fast = 5mS, Slow = 25mS) *
o Make-up gain 0dB to 20dB in 2dB steps
o Recovery (release) 400mS, 800mS, 1.6S & Auto
o Threshold -20dBu to +10dBu
Limiter: (Class A) amplifier design
o Dual attack speeds (Fast = 100uS, Slow = 5mS) *
o Recovery (release) 100mS, 200mS, 800mS & Auto
o Threshold +4dBu to +12dBu (in 1dB steps)
Stereo link via either the backplane edge connector, an XLR or both
Illuminated meter selectable for input, output or gain reduction metering.
Power off signal bypass
Entirely stainless steel chassis.
Total current consumption 150mA (per unit)
Also available supplied as a pair in a box containing a "mono/stereo" switch

These are the default factory settings however the;
Compressor "Fast" may be internally jumper selected to 0.5mS
Compressor "Slow" may be internally jumper selected to 50mS
Limiter "Fast" may be internally jumper selected to 1mS
Limiter "Slow" may be internally jumper selected to 25mS

Simplified block diagram:


Lead times may apply.
  • Model: 54F50
  • Manufactured by: Audio Maintenance Limited