If a manufacturer is able to make recorders like the C37, A62, A80 mixing consoles like the 900 series they are certainly able to produce input transformers.
Yes Studer made their own audio transformers.
Polygram ordered large quantities for the mixing consoles that were designed and build in Baarn, the Netherlands.
Studer and Polygram are history, no more excellent analogue equipment from these companies.
btw Studer also manufactured their own recording and playback heads.
For a designer small transformers that do not transfer power are easy to design.
Sonic quality depends largely on the sort of metal used for the core.
Designing output transformers for tube amplifuers is a different piece of cake.
Minimum distortion at low frequencies and a large bandwith like 150 Khz are not easy to combine with power transfer.
Partridge in the UK and Unitran in the Netherlands made those.
Famous American tube amps like MacIntosh and Harman Kardon were based on superior output transformers.