Repair of a Rogers A100 Integrated Amplifier

This old Rogers amplifier had a problem with the power amp section on one channel. Transistors had been replaced previously but issues remained.

The power amp module is so well laid out it was easy to reverse engineer and simulate. Back to the circuit and after some hunting around we find an instability issue that meant high currents were being drawn. With this understood all is looking well until we look at the distortion measurement. Something was amiss and I suspect the transistors that were previously fitted may not have been the real deal. Replacing the transistors with some modern equivalents got things sorted out.

These old amps are so time consuming and normally wouldn't make economic sense to repair. The Rogers name intrigued me however since the first loudspeakers I bought were the Rogers LS6. I still use these in my workroom today.

Future work - Possibly...
1. Change the op-amp for something quieter and look at the stability of the circuit.
2. Upgrade the volume control.
3, Reduce the gain - with a signal from a modern source the volume control is barely off zero.