Are there any major diferences between the "BETA 58A" and the older "BETA 58"?
The Beta 58A has a completely new cartridge in it. While the new cartridge is meant to mimic the old cartridge as far as polar pattern, output level, and frequency response goes, it is a different cartridge and will sound slightly different. Two major differences are that we removed the hum bucking coil on the new model and added an output transformer.
The difference between the Beta 57 and the Beta 57A is the same as the Beta 58 vs Beta 58A.
Beta 57A and Beta 58A Comparison: Beta 57A and Beta 58A Comparison