The Retro Instruments 176 all-tube limiting amplifier is a modern spin on a classic Bill Putnam design, with new features and a stunning tone that must be heard to be believed for lead vocals. This variable-mu limiter makes for ultra-smooth compression regardless of how much gain reduction is happening and can be fine tuned with modern controls like sidechain high-pass, the utterly unique Vocal Asymmetry tool, and four switchable ratios.