I am presently laying out a small add-in board for the Altair Clone that will fully implement the functionality of the 88-ACR Cassette Interface board set. This includes the addition of a third serial port for the Clone and the audio modem for actually connecting to a cassette recorder. Connection to the cassette recorder is through two 3.5mm phone jacks on the rear panel just as it was on the original Altair.
The serial port is also broken out as another DB-25 on the rear panel so it can be used as a standard serial port when not needed for cassette I/O. The additional port can be configured as a port from the 88-SIO or 88-2SIO board. Give Timesharing BASIC with three users a whirl!
Mike