I do not think there are any changes in the amps at all over the years. If there are, can you confirm what they were? I am quite certain there are not any.
There is no difference between a pass amp built yesterday or 9 years ago. When a change is made the model changes. If the model has not changed then nothing else has either since the original design.
My comments are based on a conversation with Pass Labs two years ago. I had called to ask about the changes on the rear panel between earlier and later versions of the X250.5 The RCA and XLR connectors are located differently on later models.
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