The Council may, by ordinance, issue general obligation bonds to an amount not exceeding that authorized by the general laws of Ohio, now in effect or hereafter enacted, for any purpose for which bond issues are authorized by state law. Issuance of general obligation bonds beyond the limitations imposed on Council by state law and the state constitution, shall be dependent upon the approval of such issuance by the voters, as provided by law. Mortgage revenue bonds, special assessment bonds and all other notes or bonds exempted by statute shall not be included in calculating the net debt.