https://parterre.com/people/david-portillo/?pb_company=Opera%20Philadelphia
David Portillo Archives - Parterre Box
david portilloparterre boxarchives
https://operawire.com/a-tale-of-two-seasons-david-portillo-on-fidelio-the-exterminating-angel-contributing-to-the-evolution-of-opera/
A Tale of Two Seasons - David Portillo on 'Fidelio,' 'The Exterminating Angel' & Contributing to...
Mar 23, 2017 - The high and low notes from around the international opera stage
tale of twothe exterminating angeldavid portilloseasonsfidelio