_https://www.bursonaudio.com/products/supreme-sound-opamp-v5i/
_https://www.bursonaudio.com/products/supreme-sound-opamp-v5/
_https://www.bursonaudio.com/products/supreme-sound-opamp-v6/
_https://www.head-fi.org/showcase/burson-audio-supreme-sound-opamp-v6-vivid-and-classic.23186/reviews

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_https://www.partsconnexion.com/newclassd-special-edition-opamps.html
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_https://sparkoslabs.com/discrete-op-amps/
_https://www.partsconnexion.com/sparkos-opamps.html

_http://sonicimagerylabs.com/products/products_top.html

_https://www.partsconnexion.com/semi-opa-mono.html
_https://www.partsconnexion.com/opamp-modules.html

_http://home.att.ne.jp/delta/myrobalan/opamp.html