My professor is at a loss
can you help?
Im required to use an LM386 in an audio amplifier project with an 8 ohm speaker. The thing is it doesnt seem to work. I set up the opamp as seen in the first figure on page 5 of the data sheet (http://www.ti.com/lit/ds/symlink/lm386.pdf) which should give me a gain of 20. Two interesting things happened. First, I only get the signal I input back out if I use the oscilloscope probe on AC 50 ohm, if I change it AC 1M ohm the signal becomes unrecognizable. Second, when I can actually see the signal coming back out it has a gain of 1. If I remove the input however the amplifier does in fact amplify the noise. If I put in a .1Vpp signal I get out a .1Vpp signal but the noise is amplified so much that it looks like a square wave bouncing between the rails.
So can anyone explain to me why my signal would be destroyed by changing from 50 ohm to 1M ohm?
And if you are familiar with the LM386 can you please let me know if you have encountered this issue before? I have to use this part and Im really not sure what to do about the behavior Im getting.
I appreciate any help I can get.
Im required to use an LM386 in an audio amplifier project with an 8 ohm speaker. The thing is it doesnt seem to work. I set up the opamp as seen in the first figure on page 5 of the data sheet (http://www.ti.com/lit/ds/symlink/lm386.pdf) which should give me a gain of 20. Two interesting things happened. First, I only get the signal I input back out if I use the oscilloscope probe on AC 50 ohm, if I change it AC 1M ohm the signal becomes unrecognizable. Second, when I can actually see the signal coming back out it has a gain of 1. If I remove the input however the amplifier does in fact amplify the noise. If I put in a .1Vpp signal I get out a .1Vpp signal but the noise is amplified so much that it looks like a square wave bouncing between the rails.
So can anyone explain to me why my signal would be destroyed by changing from 50 ohm to 1M ohm?
And if you are familiar with the LM386 can you please let me know if you have encountered this issue before? I have to use this part and Im really not sure what to do about the behavior Im getting.
I appreciate any help I can get.