Synergy Amps works with both boutique amp builders and popular mass amp builders alike to design their preamp sections  into a compact module, that slides into a compact preamp housing made by Synergy,  This enables guitarists to get the preamp tone of a boutique amp, like a Soldano, Bogner, Diezel etc. at an affordable price (each module is around $400). The modular preamp system was original invented by Bruce Egnator, who then collaborated with Randall on their modular Randal MTS series. The Boutique Amps collective has revived the concept with the Synergy brand name - but this time with more boutique amp brands on board to provide a wider choice of modules. The design means the modules are easily swappable.  Each module is 2 channels, so it can hook up to an existing amps effects loop, giving that amp 2 extra tube channels, and has a silent line out with cab sim for recording studios or to go straight into the mixing board. Synergy also make amp heads and combos which accept these swappable preamp modules.

Source: Synergy Amps website (28 March 2022)