On Dec 21, 2:45*pm, "Tom, N3IJ" wrote:
Can anyone suggest a source of a circuit or kit for a mono amp to
increase my laptop's headphone output level to line level?

As a starting point, it would be helpful just to learn what these
levels are. I want to drive a line-level transceiver input for digital
hamming.

Any suggestions would be appreciated.

Line Level for consumer audio is -10dBV or 0.316V RMS or just below a
volt peak-to-peak. Solid state audio equipment typically has an input
impedance in the kohm range.

Usually a headphone jack has more than enough output. Some sound cards
or laptops are "energy smart" and turn off the output if they don't
see a low-impedance load plugged in. Other times they have their own
volume controls that can be overridden by Windows and sound card
settings. Other times common-mode noise can dominate (drowning out the
signal) giving a very real advantage to using an isolation
transformer. There are many many articles on the web about using
isolation transformers to hook your computer to your radio.

Tim N3QE