Case No. 3) Audio Research SP-8 Preamplifier

A customer brought in an  Audio Research SP-8 preamplifier that constantly burnt a set of 12AX7 tubes every 4 months.   Careful examination of the unit suggested improper  changes had been previously made to the circuit.

To restore the preamp to factory specification, we had to:

• Replace the timer IC Module LM555

• Reconfigure and adjust Line gain to 20db

• Replace all zener diodes

• Add power on mute feature

• Reconfigure the circuit as close to factory original as possible

The preamp was bench tested to meet factory specification.

Estimated Cost: $ 500 which includes $ 150 in parts

Actual Repair Cost: $ 500.00 including parts & labor

Turnaround Time: 5 days.