Heritage Audio’s excellent stereo bus compressor - amazing on drums, bass, or the mix bus. It’s in excellent condition - includes power supply. (I don’t have the original box, though). With multiple side-chaining options, and a wet/dry mix blend control, this box is incredibly versatile.

Here’s what Heritage Audio has to say about it: A fully Carnhill transformer coupled input and output unit, the Successor is a true-stereo diode bridge-based bus compressor with advanced sidechain filtering and built-in parallel processing capabilities, with the Class A 73 type output stage that Heritage Audio is famous for.

Carnhill input transformers are hand wound at the Oxford factory exclusively for Heritage Audio, enclosed in green mu metal cases for modern day studio noise immunity. The vintage character is indeed guaranteed and you won´t find them in any other brand´s products. Based on legendary vintage diode designs, the Successor keeps the sonic character of such units, but the added features have already taken it into legendary status on its own. It is a new beast on its own and will make your mixes shine in modern production environments.

Ultra-fast attack and releases allow for larger than life drum bus compression sounds, while the sophisticated sidechain filters let you sculpt your mix in ways not previously possible. Snare drums can be more present and the stereo image widens as there is more natural room for tracks to breathe. From FET-like, all-buttons-in drum sounds (and in stereo!!) to VCA style mix bus with the added warmth and fatness only custom transformers can supply, the Heritage Audio Successor is designed to live permanently hooked up to your mix or instrument buses and make your mixes shine.

Warren Huart does a pretty in-depth run-through of what this thing can do, and I've linked to that video in the listing. It really sounds awesome - even if you bypass the compression, you can still drive the input to get those transformers working for you!