Questions about supply

[msr]

Hello,

I want to make this little amplifier: http://runoffgroove.com/ruby.html

However, I added an LED indicating power on and I also would like to be able to connect it to external power supply (transformer) instead of a 9V battery.

The transformer I have here is rated for 9V and 500mA. Should I have further precautions with this circuit? http://i195.photobucket.com/albums/z...dae/cicuit.jpg

I didn't find in J201 datasheet an absolute maximum value for drain-source current. Isn't it important?


Thanks in advance for your attention!

[MikeML]

Make sure your Wall-Wart is "rectified", and "filtered"; better yet, get one that is "regulated". If it isn't, you will have "hum", and you might end up having to add a voltage regulator like an LM317.

[russ_hensel]

The wall wart should be fine, but many do not produce the voltage/current as per spec. Check voltage with volt meter, nice to look at output with scope for noise and ripple. If you get a lot of hum from your circuit it is probably from the wall wart, check by replacing with a battery.