A method and apparatus for production of a yarn, by plying, twisting or covering several staple yarns, subjected to a prior transformation, is provided. At least one of the staple yarns is different from the others and/or is subjected to a different prior transformation. The prior transformation may be carried out in parallel in the same machine, by independent transformation members able to be independently controlled. A slackening of yarn tension resulting from the prior transformation to give the desired tension at an assembly point is carried out on yarn feeding devices. Routing of the yarns is achieved by guide members towards the point of assembly, where the staple yarns are combined and arranged in parallel. A bobbin receives the assembled yarns in a device, constituting or associated with a positive feed device operating without slippage with relation to the yarn. The yarn bobbin with assembled yarns is then placed on a spindle of a twisting machine for a second double plying, twisting, or covering process.