BuddyPress.org

I created a custom filter for my BuddyBar though not having a function to work with,
eg: $BuddyBar_logo = '<a href="' . bp_get_root_domain() . '" id="admin-bar-logo">' . get_blog_option( bp_get_root_blog_id(), 'blogname' ) . '</a>';

I don’t know how to remove the initial echo in $bp_adminbar_logo

// **** Custom BuddyPress admin bar logo ********
function custom_adminbar_logo() {

echo '<a href="' . bp_get_root_domain() . '" id="admin-bar-logo"><img src="' . get_stylesheet_directory_uri() . '/_inc/images/custom_logo.png" alt="logo" /></a>';

}
add_filter ( 'bp_adminbar_logo' ,'custom_adminbar_logo' );