Audiophilepure

https://www.stereophile.com/content/dan-dagostino-master-audio-systems-progression-m550-monoblock-power-amplifier

Following late-night phone consultations with Editor Jim Austin, I awoke to speak with Bill and Dan about the possibility of delaying the review and sending the amps back to Arizona for repair. Dan, though, was certain that the amps were fundamentally sound. He thought the discrepancy was caused by a shift in biasing, which presumably happened during shipment.

Two tension-fraught days later, Hans Brackmann, Definitive Audio’s store manager, drove to Port Townsend to rebias the amps. All D’Agostino dealers are prepared to rebias the M550s whenever necessary.

Sure enough, rebiasing was called for—just that, nothing more. By the time Hans left, both channels sounded the same (save for minor discrepancies caused by room imbalances), and I heard even more of the beautiful, smooth, finely detailed, impeccably controlled, remarkably dynamic, slightly warm and glowing sound that had made me fall in love with the Progression M550s.