Normally one would say, the grey Music Synthesizer is for the North American market and the brown one is for the international market.
But from the three brown Synthesizers I own, one has the NA labels on it. It seems a small amount of brown ECS stuff was made for people who wanted fitting extensions for their Intellivision I.
Maybe that's already known.
My four Music Synthesizers:
The International label with model no. 4630:
The NA labels with Model No. 4188 and also the special orange label:
Edited by Intymike, Sun Dec 30, 2018 10:49 AM.