SimpleMembership password hash compute

Hi, i'm using simple membership provider. I would like to replace it with custom membership provider. Bu i have to compute password for validate user from Db. i researched and found  a method for this but, password doesn't match with DB values. Method generates smaller length and wrong passwords hash. And in webpages_Membership table PasswordSalt field always blank string? How can i hash password same as db and simplemembership. thanks for your help
method value for 123456 btWDPPNShuv4Zit7WUnw10K77D8=
db value for 123456  ABtYn2fEmwcXXMp7aGDLetIx0TmdD4RwSrFyFNd2+9NqdwnVo1+fdn0fmAjH7enG+w==

public string EncodePassword(string pass, string saltBase64) { byte[] bytes = Encoding.Unicode.GetBytes(pass); byte[] src = Convert.FromBase64String(saltBase64); byte[] dst = new byte[src.Length + bytes.Length]; Buffer.BlockCopy(src, 0 ...