A modular synthesizer that incorporates a mix of modules from two or more formats. Mixing formats can be a way of expanding the functional possibilities of a modular synth by providing access to lines of modules from more manufacturers, and also sometimes of saving money via being able to purchase certain modules in formats or from manufacturers from which they are less expensive.
Problems that must be overcome in building a Frankensynth modular include differences in power supplies, signal voltage conventions, and physical mounting. All of the five major formats use different patterns of module mounting holes; in some cases it is possible to buy or build mounting rails that have the necessary hole locations for multiple formats, but mixing can leave odd-sized gaps between modules due to different module-to-module spacing. Mixing small-format modules (Eurorack or Frac) with large formats involves mounting the small-format module in an adapter that bridges the gap between the wider mounting rails. Power supplies use different connector types between the formats (in most cases; MOTM and Frac do use the same connectors), and in the case of Eurorack or vintage Moog modules, different supply voltages. There may also be differences between signal formats and connectors used; a particular problem in mixing Modcan-A with other formats is the fact that the Modcan-A banana jacks do not provide grounding continuity. (Modcan-A modules being mixed with MOTM or Dotcom formats are sometimes modified to replace the banana jacks with the 1/4" phone jacks used by those formats.)