Monday, October 23, 2017
Finally a 2SK669 AF amp for the project.
The transformer could be a homemade one such as this
homemade transformer or a line transformer. A Bogen model T725 should work. Even a 12 volt filament transformer would do the job.
I found the biasing to be to easy to mess up with a voltage divider. The standard parts don't match the required values and we end up with a 40 - 60 ma drain on the battery. Using the self bias/feedback it is much easier to let the circuit balance itself. This circuit has less than 6 ma drain and will drive the headset or earbud very hard with a reasonable drive.
Posted by Reset at 12:42 PM