Ketron and Generalmusic keyboards do not sound the same. What you might have seen is that there is a distibutor in Germany who's company name is "Solton".
Solton used to be the brand name Ketron keyboards were known as. You would see on a Ketron keyboard a large name "SOLTON" with a smaller "by ketron" below it.
This is because Ketron made keyboards for this German distributor with the distributors name "Solton" on it.
A few years ago, this distributor decided it wanted to sell Generalmusic keyboards as well as Ketron keyboards and so Ketron stopped naming their keyboards Solton and only put the Ketron name on them.
Generalmusic took their Genesys keyboard and called it "Solton SG1" which confused a lot of people because they thought Ketron was making this keyboard and not Generalmusic. However, it was really a Generalmusic Genesys with the distributors name it wanted on it.
This is really confusing, I hope you understand.
Kaye's Music Scene