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LM386 audio amp-based feedback box

vege420

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Hi everyone :)
So I'm planning to make an amplifier circuit, like shown in the picture attached.
Except I want to add an audio output, so I can e.g. record the signal that goes to the speaker. How should I go about this? Where should I mount the 6,3 mm jack?
Also, can somebody proofread this diagram for me? I'm a total noob.
I won't install the LED and resistor though, if that's important.
Thanks in advance.
 

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KlausST

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Hi,

LM386 is an old, low quality, low power audio amplifier.
I recommend to buy a modern one. There are many cheap modules on ebay and other marketplaces.

The speaker signal usually isn´t the signal you want to record, because it is more noisy and more distorted than the amplifier input.
--> Use the amplifier input signal.

Klaus
 

    vege420

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danadakk

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Some cheap alternatives here, even bluetooth ones.




Regards, Dana.
 

Audioguru

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What is a "feedback soundbox"? The power of this circuit into an 8 ohm speaker is only 0.45W.
What is its input? An electric guitar needs a preamp with a 1M or higher input resistance. This circuit is only 25k or less.
The gain of 200 times is too high for an electric guitar.
The 10uF C1 input capacitor value is 100 times too high, use a 100nF film capacitor.
The 100uF C3 output capacitor value cuts all bass sounds below 200Hz.
The 1uF value of C4 is much too small. it should be the same value as C3.
The extremely important RC zobel network from the output to ground is missing. EVERY schematic in the datasheet shows it.
 

KlausST

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Hi,

LM386 is not a classical Opamp. According TI datasheet it is a "Low Voltage Audio Power Amplifier". It is designed to drive low ohmic loudspeakers.

Out of curiosity I did an ebay search. There is much crap around. Some data given are just unrealistic "advertising values".

Now how to get meaningful reliable values?
* find out what hip (IC) is used. Best: Manufacturer and exact type. Example: "TPA3116"
* then do an internet search for: "TPA3116 datasheet"
* the values given in those originnal manufacturer datasheets should be reliable.

You should look at
* output power (depends on speaker_ohms, supply voltage, expected distortion....). I'd say 3W should be sufficient for normal listening (not very loud). 50W will be quite loud. Don't choose the highest power, choose one that fits your needs.
* distortion. For quite good sound I recommend it to be below 0.1% at the expected loudness. The lower the better.
* Amplifier class:
- Class A, AB, B are linear amplifiers (descending quality). They may get hot, may need a heatsink at quite low output power
- Class D is efficient, quite high output power even with no or a small heatsink. The output is digital switching, it can't be used as input for other sources like "recording". They come with or without output filter (LC low pass). I'd choose one with output filter.
* Those modules need DC power supplies. Look at the datasheet which voltage to choose, don't choose one with higher output voltage!
Amperage is less critical. Too low amperage will be fine for low output power, but will cause to distortion or malfunction at high output power (loudness). To high amperage is no problem at all. Maybe you need extra capacitance maybe extra filters in case you hear some noise (hiss) at low volume.

Klaus
 

Audioguru

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My question about "What is a Feedback Soundbox" was not answered. Google also does not know.
I suspect it is a speaker in front of a musician so that he can hear the other players and his own instrument from it. The puny 0.45W from an LM386 would be useless but could drive headphones. Maybe a 10W amplifier would be good.
 

danadakk

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