Private Sub IPAtext_KeyPress(sender As Object, e As KeyEventArgs) Handles IPAtext.KeyDown
    Dim AChars() As Char = {"æ", "ɑ"}
    Dim Counter As Integer = 0
    Select Case e.Modifiers
        Case Keys.Control
            Select Case e.KeyCode
                Case Keys.A
                    While e.Modifiers = Keys.Control And e.KeyCode = Keys.A
                        IPAtext.AppendText(AChars(Counter))
                        '-- Pause for keypress. If keypress =/= A then complete loop, if keypress is A again then increase counter. --
                        Counter = (Counter + 1) Mod AChars.Count 'Increments the counter so that it cycles back to 0 when it goes past the count of AChars.
                        '-- Only execute the line below if keypress is A. --
                        IPAtext.Text = IPAtext.Text.Remove(IPAtext.TextLength - 1) 'Remove the last character from the textbox.
                    End While
            End Select
    End Select
End Sub

Private Sub RichTextBox1_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles RichTextBox1.KeyDown
    e.SuppressKeyPress = True
    e.Handled = True

    Select Case e.KeyCode
        Case Keys.A And e.Modifiers = Keys.Control
            RichTextBox1.SelectedText = GetCharacterToPrint(RichTextBox1.SelectedText, New Char() {"æ", "ɑ"})
            RichTextBox1.Select(RichTextBox1.SelectionStart - 1, 1)
        Case Else
            e.Handled = False
            e.SuppressKeyPress = False
    End Select
End Sub

Private Function GetCharacterToPrint(ByVal SelectedText As String, ByVal Characters As Char()) As Char
    If SelectedText.Length <> 1 Then
        Return Characters(0)
    End If
    Dim c As Char = SelectedText(0)
    Dim index As Integer = String.Join("", Characters).IndexOf(c)
    If index = Characters.Length - 1 Then
        Return Characters(0)
    Else
        Return Characters(index + 1)
    End If
End Function

Private Sub RichTextBox1_KeyUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles RichTextBox1.KeyUp
    If e.KeyValue = Keys.ControlKey Then
        RichTextBox1.SelectionStart += 1
    End If
End Sub