lm386 amp circuit problem

lm386 circuit

hello. i'm currently bread boarding a 386 amp circuit and i'm having a problem. I am trying to amplify the signal from my casset player to a small 8ohm speaker. I can faintly hear some sound coming from the speaker, but its very faint. (i'm also getting some kind of oscillation at higher volumes but i'll worry about that later) The speaker is only outputting at about whisper volume. Any idea why it would be doing this. Heres the schematic and a picture(sorry kinda hard to see some of the component locations) . Any help would be greatly appreciated.

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lm386

why would be 10r and 47nF is there ?

the whisper amplifier circuit

Looking at the schematic, it looks perfect. It should work provided it is constructed as it is in the schematic and you get 9volts at pin 6 and ground to pin 2 and 4. But when you say you have constructed it on a bread board, cross check all the connections individually, and too remove the POT and test for audible click when you touch the input. Good luck

oscillating lm386

Dipnirvana, the capacitor and resistor form a Zobel Network and are to compensate for the inductive reactance of the loudspeaker. The loudspeaker and network in parallel appear more like an ideal resistive load to the amplifier.

I am concerned about the oscillation at high volumes. Almost certainly, the oscillation is there all the time but not noticeable until the volume is turned up. Bad layout could be the cause but the first thing to try would be moving the 10uF capacitor across the battery so it is right across pins 4 and 6 of the LM386 and with wires as short as possible. Personally, I would use 100uF or more and add 10nF in parallel.

Also make sure the bottom of the volume control and the 1nF capacitor are returned to ground close to pin 4 of the chip. If there is any voltage drop in the ground wiring around the input, it could be seen as additional signal at pin 3 of the IC and get amplified. Relatively large currents flow around the supply pins and loudspeaker wires so these would be the most likely to cause voltage drops. Ensuring the output currents and input voltages are kept apart should help to make it stable again.

Brian.

lm386 amp

If the circuit is made on a pcb or on stripboard with a good layout then the IC will not oscillate.

lm386 layout

I think you're shorting out you input signal by using a stereo 3.5mm socket on a mono cinch to 3.5mm jack converter (pink and cyan wire). The wire which would carry the right side signal in a stereo application is shorting your signal to ground on the mono plug.

Only the wire which connects to the tip of the jack plug should be used (pink or cyan, hard to tell from the picture) along with the gray groundwire.

lm386 circuits

An audio circuit on a breadbord is not always a good combination, there is chance for oscillation.
Anyway, you do need to put a bypass capacitor of around 100nF and a bypass elko of about 100uF over the power supply pins of the LM386.