Questions about supply

Discussion in 'General Electronics Chat' started by msr, Feb 24, 2010.

  1. msr

    Thread Starter Well-Known Member

    Jul 8, 2008

    I want to make this little amplifier:

    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?

    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!
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    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.
  3. russ_hensel

    AAC Fanatic!

    Jan 11, 2009
    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.