Automated Processes, Inc. (API™) has been making its model 2520 discrete op amp since the 1960s and continues to manufacture it today. While a 2520 can be recognized by its distinctive midrange timbre, there have been at least five different revisions over the years, each with its own variation on this theme. The new ones are no longer available for sale from API, so you have to either search the used market or purchase something similar from another company. Supposed substitutes are the Seventh Circle Audio SC25 and Avedis Electronics 1122.
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