Solder iron not hot enough for PC board

Of course Western companies have factories in China that have excellent quality control. But many no-name-brand manufacturers in China make millions of fake parts and poorly made modules that are sold by "sellers" on ebay, Ali... and Amazon. The counterfeiters have no quality control and sell cheap junk.

I buy genuine name-brand Western parts from Western distributers like Digikey and Newark because the parts and delivery times are excellent and I want them to keep in business.

This 1000 gain circuit does not work. It makes no sound at all. It took about 2 minutes for the IC to get hot enough to burn my finger using 7 AA batteries in series. Capacitor & resistor on pin 1 says 22 and 100uf. I assume 22 = 22 ohms.

I found a circuit almost like this the main difference it is the typical LM386 circuit with pin 2 grounded and a capacitor resistor connected to pin 8 not pin 1. Resistor value on pin 8 is 2.2K and capacitor is .1uf.

Next thing to do is remove 100uf cap from pin 2 the connect pin 2 to ground. Remove resistor and cap on pin 1 then connect pin 1 to 8 with 10 uf cap it should work as long as the IC is not fried.

Bottom circuit should work but might not be gain 1000. I think these are more of those FAKE circuits people put online. I will change it to gain 200 about 30 minutes work. I am not trying the other 1000 gain circuit I don't believe it works either.

I did Google search and found a 3rd circuit that claims to be gain 1000.

gary350 said:

Only difference is, China workers get paid about $1 per day and American Union workers are not getting paid $87 per hour anymore

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You forgot to add that the company didn't drop its price, to reflect the difference.

shortbus= said:

You forgot to add that the company didn't drop its price, to reflect the difference.

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Labor is not always the biggest cost. The Chinese guys are buying used fab equipment for pennies on the dollar vs new, the high purity Chemicals used for the vapor deposition processes are much cheaper in China because of, again. Labor, capital and stuff like this that was less well enforced there than in the US until 2015. Interestingly, China shut down a significan number of chemical manufacturing facilities in 2015 and 2016. Care to guess how many (approximately).

Gary, you have all the noise on your power supply feeding into the pin 2 input of the LM386. But pin 2 is supposed to be connected to ground, pin 4.
Your 100uF capacitor that is feeding all the power supply noise into input pin 2 is supposed to feed some of the power supply noise to ground and not feed anything into pin 2.

Then you show a 2200 resistor feeding a 0.1uF capacitor from pin 1 to ground. Then 1/(2 x pi x 2200 x 0.1uF)=727Hz. Then squeaky frequencies above 727Hz are boosted a little.

The datasheet for the LM386 says that the gain can be increased with a series RC to round on pin 1.
I found the article on the web that talks about boosting the gain with a series RC to ground on pin 1. It shows a few high gains and 1000 is with 22 ohms and a 100uF capacitor that cuts deep bass sounds.

audioguru said:

Gary, you have all the noise on your power supply feeding into the pin 2 input of the LM386. But pin 2 is supposed to be connected to ground, pin 4.
Your 100uF capacitor that is feeding all the power supply noise into input pin 2 is supposed to feed some of the power supply noise to ground and not feed anything into pin 2.

Then you show a 2200 resistor feeding a 0.1uF capacitor from pin 1 to ground. Then 1/(2 x pi x 2200 x 0.1uF)=727Hz. Then squeaky frequencies above 727Hz are boosted a little.

The datasheet for the LM386 says that the gain can be increased with a series RC to round on pin 1.
I found the article on the web that talks about boosting the gain with a series RC to ground on pin 1. It shows a few high gains and 1000 is with 22 ohms and a 100uF capacitor that cuts deep bass sounds.

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You posted that 1000 Gain circuit didn't you notice it was wrong. Both 1000 Gain circuits are wrong. I knew circuit did not seem right when I built it pin 2 was connected to the power supply that is wrong. I changed pin 2 to ground. I put 10uf cap across pin 1 and 8 the 200 gain circuit works good. The IC that got hot still works good.

The circuit for the gain of 1000 times is correct and is the same as the second circuit of it that I posted. They show pin 2 connected to ground like all the other parts including the 100uF that are also connected to ground.
Your first circuit has pin 2 connected to the 100uF capacitor that connects to the positive supply but your pin 2 is not connected to ground. Your second circuit with pin 2 grounded, the 100uF power supply capacitor missing and the 22 ohms resistor replaced with 2200 ohms probably has a gain of only 21 times.

Your circuits with the gain of 1000 times are also missing the 1k ohms and 100uF to ground filter that feeds power to the 10k resistor that powers the electret mic which might cause very high frequencies to be amplified 1000 times and cause the IC to heat up.

After you connected pin 2 to ground (and add the RC above) did the gain of 1000 times work?

This is the best and final circuit. I had lots of trouble with R2 volume control making lots of static every time I turned the knob there was noise like a rock crusher at full volume even with volume control set low as it goes. I swapped volume controls 2 times that did not fix it. I only had capacitor C2 in the circuit so I added C1 and static was gone. Wow it sounds nice no static at all even from turning the volume control. I changed C8 to 470uf. Sound is crystal clean. I have been using 7 AA batteries until now. Today I put a power supply plug on the circuit board for a 12vdc power supply inverter for 120vac. Output of the inverter with no load 14.08 vdc. Wow what a different 3 extra volts makes mic sensitivity is much better and output volume seems to be 20% louder and it probably is. Notice the PC board is upside down on purpose those copper things are too close together. Do not use ceramic caps in this circuit.

Goody.

gary350 said:

I had lots of trouble with R2 volume control making lots of static every time I turned the knob there was noise like a rock crusher at full volume even with volume control set low as it goes. I swapped volume controls 2 times that did not fix it. I only had capacitor C2 in the circuit so I added C1 and static was gone. Wow it sounds nice no static at all even from turning the volume control.

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You've been told repeatedly that C2 isn't needed, so why keep fitting it?. However, C1 is absolutely essential as without it you have DC through the control which causes nasty noises.

Nigel Goodwin said:

You've been told repeatedly that C2 isn't needed, so why keep fitting it?. However, C1 is absolutely essential as without it you have DC through the control which causes nasty noises.

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YOU r right but with C2 there is less static. I removed C2 then I put it back. Sound is better less noise. Explain that?

gary350 said:

YOU r right but with C2 there is less static. I removed C2 then I put it back. Sound is better less noise. Explain that?

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The datasheet shows that the input bias current is about 250nA. In the 50k input to ground resistor, that makes an input voltage of about 12.5mV which could be more. The 12.5mV might cause noise in your volume control when it is turned especially since your gain is fairly high. C2 blocks that DC voltage on the volume control.

audioguru said:

The datasheet shows that the input bias current is about 250nA. In the 50k input to ground resistor, that makes an input voltage of about 12.5mV which could be more. The 12.5mV might cause noise in your volume control when it is turned especially since your gain is fairly high. C2 blocks that DC voltage on the volume control.

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As you're well aware AG, there's no such capacitor suggested in the datasheet, but I suppose with the excessive gain in use here the minute bias current could cause a little noise.