Impedance matching audio transformer windings
1 M ohm input impedance is massive for a transformer. Consider just the primary on its own - forget about the load on the secondary. The primary is just an inductor and it must have greater than 1M ohm impedance at (say) 80 Hz.

XL = 1,000,000 = 2\$\pi f L\$ therefore L = nearly 2,000 henries.

If the ferrite has an \$A_L\$ value of 10uH per turn squared you'll need over 14,000 turns.

BTW 80 Hz corresponds to "low E" on the fat string on a guitar.