Myhill spent last season away on-loan and may play second fiddle to Ben Foster this season.
Ridgewell said of Foster: "All credit to the chairman for getting him signed up.
"Boaz isn't a bad lad to have as a No.2 either. I know him well from my time at Villa and he has gone from strength to strength.
"There can't be many Premier League clubs who have two such brilliant goalkeepers."