Powershell Script Issue with SQL Server 2012/2014

I have a PowerShell script which works well when I run it on server with SQL Server default instance (MSSQLSERVER) but the same script fails on a server with a named instance (MSSQL$instance)

For the default instance (MSSQLSERVER)

[Reflection.Assembly]::LoadWithPartialName("Microsoft.SqlServer.Smo")
$service = Get-service -name 'MSSQLSERVER'
$status = $service.status
$CreateDB = "db-Test"

if ( $status -eq "Running" )
{ 
    'Success' | Out-File -FilePath c:\sqltest.log -Encoding ASCII

    $srv = new-Object Microsoft.SqlServer.Management.Smo.Server("(local)")
    $db = New-Object Microsoft.SqlServer.Management.Smo.Database($srv, "$CreateDB")
    $db.Create()
    $db.CreateDate
}
else
{
    'Failed' | Out-File -FilePath c:\sqltest.log -Encoding ASCII
}

Above script works very well. But below script throws error :

For named instance :

[Reflection.Assembly]::LoadWithPartialName("Microsoft.SqlServer.Smo")
$service = Get-service -name 'MSSQL$instancename'
$status = $service.status
$CreateDB = "db-Test"

if ( $status -eq "Running" )
{ 
     'Success' | Out-File -FilePath c:\sqltest.log -Encoding ASCII

     $srv = new-Object Microsoft.SqlServer.Management.Smo.Server("(local)")
     $db = New-Object Microsoft.SqlServer.Management.Smo.Database($srv, "$CreateDB")
     $db.Create()
     $db.CreateDate
}
else
{
     'Failed' | Out-File -FilePath c:\sqltest.log -Encoding ASCII
}

Above script for named SQL instance throws below error :

New-Object : Exception calling ".ctor" with "2" argument(s): "SetParent failed for Database 'Netmagic-Test'. "
At C:\mssql-test.ps1:11 char:7
+ $db = New-Object Microsoft.SqlServer.Management.Smo.Database($srv, "$CreateDB")
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [New-Object], MethodInvocationException
+ FullyQualifiedErrorId : ConstructorInvokedThrowException,Microsoft.PowerShell.Commands.NewObjectCommand

You cannot call a method on a null-valued expression.
At C:\mssql-test.ps1:12 char:1
+ $db.Create()
+ ~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull

Error Screen

Thanks,

Viral