I'm thinking of building this circuit below, but want to use a line level input instead of a microphone. I've made an edit to the circuit, also attached. Is this the correct way to do it?? I'm not sure about the 4.7k resistor either.... Can anyone give any guidance?
Cheers
Lee

 

I'd say leave out the 4k7 resistor, throw in a 10k audio taper potentiometer, and you're done.

 

Thanks - for a headphone input - the same? could leave out the pot if using volume on source?

 

I think so. There are only a few headphones with higher impedance so I assume your, "headphone" output is designed for the low impedance type.

 

Worked well.... thanks for the tips....
I ended up just plugging the output of a 1kHz 555 square-wave on the input there and the little transmitter worked nicely, albeit just transmitting an annoying tone over a couple of metres, but it worked....

 

Keep in mind crystal mikes are very HOT...so you may not need much more attenuation.