The sound board amplifier output stages shown, are from late 1970s monochrome arcade machines.
They both use a push pull amplifier but differ slightly.
The earlier one has the volume control in the feedback to the op amp, the other varies the I/P to the op amp.
My question is the technical function of the diodes (D6, D7) between base/emitter of the later version.
I assume they are some form of protection.
I found the fault on the earlier version being an o/c pot in the feedback cct which caused the volume to be flat out.
I was wondering if it would be an advantage to add the diodes and emitter resistors.
They both use a push pull amplifier but differ slightly.
The earlier one has the volume control in the feedback to the op amp, the other varies the I/P to the op amp.
My question is the technical function of the diodes (D6, D7) between base/emitter of the later version.
I assume they are some form of protection.
I found the fault on the earlier version being an o/c pot in the feedback cct which caused the volume to be flat out.
I was wondering if it would be an advantage to add the diodes and emitter resistors.
