Unicord EC-80A Tape Echo: study-repair

An interesting artifact from the 70’s …

The Unicord EC-80A Tape Echo is a pretty rudimentary machine, best suited for old-school regenerated noise effects …

MAIN BOARD COMPONENT LAYOUT AND OFF-BOARD WIRING

unicord-ec-80_a-lyt

SCHEMATIC WITH WITH VOLTAGES

unicord-ec-80_a-voltages

the thing that jumps out is the class-A circuit architecture, and the amount of voltage gain generated there … the following DC-Table results

TINA-TI (OP) SIMULATION OF INPUT PREAMP CIRCUIT
using BC239C models

unicord-ec-80_a-dctest-bc239c

TINA-TI (OP) SIMULATION OF READ-HEAD PREAMP CIRCUIT
using BC239C models

unicord-ec-80a-dctest-bc239cread

50khz bias oscillator voltage, seen at the Collector of Q7

ec-80a-carrier

both tape heads are still working …

ec-80a-heads

final (adjusted) motor speed voltage range:
1.4v – 6.4v


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