I’ve just finished breadboarding the amp and the funniest thing, not only did it ‘work’ but I got 2 radio stations to boot! Yep on the same power in line to our shed I’ve got an AM radio and an FM radio plugged in so I unplugged both but still got both stations 1 AM and 1 FM playing away. So I ran a long lead to the house and amp, no change? Any ideas? Trev

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Probably a bad solder joint, those LM386 chips are just that finicky?  but if you take a real small capacitor 100pf-470pf & solder it across the signal to ground at the Input jack, this should dump it to ground before it goes into the circuit? A 100pf capacitor usually works for me, but sometimes it requires a bigger one depending how strong the interference? You may want to go back over your solder joints though?

When I said solder joints, I meant to say wire joints & jumpers? Make sure they’re plugged in solid & not sticking out too far, long exposed wires become antennas?

Hi BQ, I’ve remade the amp from scratch, with new bits(same ic) and it still plays the same 2 radio stations. I got a probe and touched here and there, touched ic pin 7(unused)and their volumes hit 11. So I remade it again with new bits, same ic and the same results? It has also a slight hum and some static but not a lot on both counts. I even put an earth on the pot, nop no different, so I’m still in the dark. Trev

Then place an 0.1uF capacitor between pin 7 & ground? Which version of the chip do you have?

Hi BQ, so I did the little cap on pin 7 and all that did was transfer the incoming am/fm signal to the pot. So I’m going to change all the parts and start again, oh and the hum & static was there with a vengeance too. Trev

It might also have something to do with your breadboard? Try building it on another section of the breadboard?  Maybe the legs are poking the ones next to it underneath? What version are you using, LM386N, or JRC386? That’s kind of weird, C3 is a noise stabilizer? But putting a capacitor to ground from pin 7 shouldn’t have any effect on pins 1/8, pin 7 bypasses the unused channel, there’s a pos. & neg. input channel on this chip? Maybe increase the size of the cap? 

Hi yet again BQ, the ic is an lm386n-1. Brand new board does the same as my 3 mth old one. Maybe the chip and both boards have cv-19? So I put a 104 between pin 8 and power in, I ran an earth from the pot, I’ve put a 100 cap on the input earth and jack mid pin , I upped the 104 to a 2.2, I’ve replaced all the components. I’m not to sure if I’ve done much else, except rebuild it about 10 times. What with our 9th lockdown, I’m going nuts. Trev

Those N-1 chips are pretty noisy, the job of pin 7 is to ground the open input & get rid of noise made by it, so I’d keep going bigger with the cap? Maybe a 10uF or better yet a 47uF? I suggest an N-3 or JRC386D chip, they are louder & operate with less noise? 

Well I’ll give it all a shot in the morning. Thanks Trev
PS. I didn’t think half a dozen bits & a dozen joints would be so unreasonable.


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