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Little Gem Amp Problem

Hi all
I am quite new to electronics but I am very interested in it. I have built a couple circuits before but nothing with an IC chip.

So now I have decided to move onto slightly more complex projects,  and I found the Little Gem Guitar Amp: http://www.runoffgroove.com/littlegem.html

I
 have built it on a veroboard from these diagrams but I changed the layout slightly. Obviously everything is connected the same way I just moved the 100uF cap a little up. I have also added a 10Ohm resistor to the output and used headphones instead of the speaker.

When I connect the 9V battery, without an audio source, I can hear is a soft buzz, quite a high frequency. The gain pot makes the noise louder and softer so I assume the LM386N-1 chip is fine.

If I put my finger on the ground part of the 1/4 inch jack, the noise become much loader and lower frequency. The same thing happens if I connect an audio source. Is there an obvious cause for this problem that I don't know about?

I have connected the jack to the board with shielded twin core wire. I have used the shield as ground and the core as signal. Is this correct?

Any help would be appreciated, I would like to get this working.



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Goodhart6 years ago
"Sounds like" you have created an "antenna" and might be picking up 60 Hz hum from AC mains in your house (if in the USA).

What Nacho suggests should help.  Make sure the ground is a good one before giving up and looking for any other solutions, if it doesn't. 

With a floating ground, electronic devices can act like an antenna, so if you don't want to go through a lot of electronic gymnastics (like trying to find the proper sized capacitor to dampen the buzz without limited your output), then the earth ground is your best bet.
geniass (author)  Goodhart6 years ago
Oh wait, very silly mistake on my part. I was using a mono cable from a stereo source so I had a ground loop and its working very well now. Thanks for the help though.
Yep, that'll do it :-)
geniass (author)  Goodhart6 years ago
Ok, I am not 100% sure what this means, and wikipedia isn't helping. Does it have something to do with having a common negative rail that all "ground" connections in the circuit connect to?
NachoMahma6 years ago
. Try connecting your circuit ground to Earth ground. You will probably still get hum when you poke certain parts with your finger, but it should diminish the hum when you have an audio input.