Auzen currently markets the following OPAMPs: OPA627AU, OPA637AU, OPA627SM, OPA637SM, AD797AR, AD8620BR

The first letter, ‘A’,’B’,’S’ means ‘OPAMP Grade.’

The quality is better in following order.

S > B > A ("S is better than B is better than A")

The second letter, ‘U’,’M’,’P’ means ‘package type’.

P: DIP type

U: SMD(SOIC-8) type

M: Metal Can type (protects against noise and electricity)

The OPA637SM has the highest price and provides the best sound quality.