Different versions of the Roland TB-303
In the past 2 decades I have seen Type A, B, C and D here in the lab.
Type D is the most common one, saw a few A's and B's and only one C.
All type A's I've seen had factory (first owner 303's that were bought new) mods/corrections arround din sync and schmitt trigger tempo circuit.
All B's I've seen had factory mods/corrections arround tempo circuit.
Some A's and B's had a factory mod on the gate circuit that slows it down. My educated guess is that this was done to accomodate BA662A's that have a bit more control current feedthrough than the original gate circuit allowed for.
Type C has no mods and the only obvious difference with type D is less pcb track spacing on the component layer.
Next to those different pcb versions and factory mods, there is also a plethora of different components used throughout it's production.
And, there is also a different bottom case. I've seen this one only once. It has extra supports underneath tempo, pattern, mode and volume pots/switches. This to protect the brittle FR2 PCB.
I'll get back with more detailed info when I went through my archives and have done a full analysis
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