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Audio amplifier: LM386

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yup. its 11:11. fortunately mum's asleep . . . if she came in here right now she'd have my head :lol: (gotta get up early)
 
Hi Zach,
Of course All Electronics stocks logarithmic pots. They just call them "audio taper" instead. Same thing.
Don't you have the datasheet for the TDA7000? I wish that I saved it because since Philips isn't making that IC anymore they don't have the datasheet anymore either. I recall that the datasheet specifies a 22K load (volume control) so 10K will be too low. A magazine project uses a 100K pot and a 10uF cap across pins 1 and 8 of the LM386 for more gain (and more hiss). It also has a pin 7 bypass cap but doesn't have the important zobel network at its output. Google links to lotsa TDA7000/LM386 projects, but they are all a little different like that. I think that you should make it according to the manufacturer's datasheet. Here is the magazine's schematic:
 

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How cum, errr why did that schematic post so BIG?

Hey John,
I am sorry to pick at your project with the LM386, and I am sorry that I mistakenly said that it has bass-boost (it doesn't).

In addition to your 0.1uF cap (C7) at its input to ground that attenuates medium and high audio frequencies when your volume control is at half-resistance, according to the datasheet your 10uF cap (C3) at pins 1 and 8 has backwards polarity!
Here is the LM386 part of the schematic that you posted and I hope that it isn't too big:
 
according to the datasheet your 10uF cap (C3) at pins 1 and 8 has backwards polarity

Argle garble! Quite right! The schematic I used from the datasheet doesn't show the polarity, I must have just [ahem] assumed, though every other circuit does show the positive on [edit] 1. I just measured the DC voltage across that cap and it's practically zero, but I'll turn it around anyway.

In addition to your 0.1uF cap (C7) at its input to ground that attenuates medium and high audio frequencies when your volume control is at half-resistance

I don't argue that for a minute, but I must have added it for a reason (maybe because the TTS was "hissy"). If I didn't like it I would have removed it. But, as it is, it's working, I ain't changing it. Hopefully Zach is going to breadboard this first and maybe he can report on it!

Thanks for the comments!

j.
 

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u bet im gonna breadboard this first!!! I wish that i could breadboard the TDA7000 part of it also, but ive had some bad experiences with high frequency+breadboard. @ least the tda7000 circuit that i have is a proven method :lol:

I just ordered all the parts i need for the tda7000 and the lm386 last night (saturday), and 2day is sunday, no mail on sunday GRRR, so monday it is!
Meanwhile, im making a little LED flashlight. Playin with electronics is what i do instead of playing video games :D

Thanx for all the help everybody
 
?????help

does anybody know if it would be possible to add pots for bass boost and gain on a single lm 386?
 
does anybody know if it would be possible to add pots for bass boost and gain on a single lm 386?
The datasheet for the LM386 shows how to connect a volume control and discusses adding a gain control pot. It also shows a simple bass boost circuit.
 
Bass boost....

thanks audioguru but what i was wondering is....to add a bass boost you need a pot between pin one and 5 and for gain you need a pot between pins one and 8, since they both connect to pin one would it be possible to make an amp with bass bost and gain controls?
 
to add a bass boost you need a pot between pin one and 5
No.
The 15k resistor between pin one and 5 reduces the gain. its value determins how much the gain is reduced but the datasheet says that the gain must never be less than 9. The 47nF capacitor stops the resistor from reducing the gain at lower frequencies so they appear to be boosted. The frequency where the gain is reduced is determined by the value of the resistor and capacitor.

for gain you need a pot between pins one and 8
No.
You need a capacitor that could have a series pot for gain adjustment.

since they both connect to pin one would it be possible to make an amp with bass bost and gain controls?
Maybe.
The datasheet says that if pins 1 and 8 are bypassed with a capacitor for a gain of 200 at lower frequencies then the resistor in the bass boost circuit can be as low as 2k for lots of bass boost but then the gain at the higher frequencies is only 9.

Maybe you need an additional bass boost circuit. Then you can have as much gain as you want.

But the LM386 has a very low amount of power (it clips at only 0.45W into 8 ohms with a 9V supply). If you boost the bass then the higher frequencies will have an extremely low max power.
 
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