# lm386 amp with Bass Boost

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#### aalauzier

##### New Member
I looked around online to find a circuit for the 386 that could give me the best sound quality to my mini subwoofer speakers, and found one in the data sheet. I copied it into eagle and changed a few things like adding a smoothing cap. and a pot so it could have two channels. I was just wondering if there are any changes that I could make that would improve sound quality or if i could change the two smaller caps, .033uf and .05uf to anything else, since I cannot seem to find them in my local Radioshack. And I was also wondering what type of cap to use as a bypass on pin 7. Thank you.

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#### audioguru

##### Well-Known Member
You mentioned sub-woofers. But the datasheet for the LM386 shows that the peak is at 80Hz and is only 6dB. Important deep bass frequencies below 80Hz are boosted less.

Did you know that the output at clipping is only 0.45W at only 80Hz and is only 0.11W at frequencies above about 1kHz?
You will not feel anything from your sub-woofers with such low power.

The 250uF output capacitor reduces output frequencies below 80Hz. If it is 1000uF then there will be more boost at frequencies from 20Hz to 80Hz.

#### aalauzier

##### New Member
Thank you, these are the answers i was looking for, but i mentioned subwoofers but they are more like midranges, i took one out of an old stereo that had 2 tweeters and this midrange speaker, and even powered by an ipod, it has good bass response. Are there any other changes that i could make to improve sound quality? And what cap should i use for bypass at pin 7. And I know that the 386 is not great, but it is cheap. Are there any other alternatives that are still cheap yet work as well?

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#### audioguru

##### Well-Known Member
Electronic ICs are very cheap.The TDA2822M amplifier produces 0.8W into 8 ohms with a 9V supply. It costs only $.66US each at Newark today. You could have much more power from amplifiers that produce 14W each and are designed for cars. The TDA7240A is a good 14W into 4 ohms amplifier when it has a 13.2V supply. It costs only$2.55US each at Newark today.

#### ronv

##### Well-Known Member
The cap on pin 7 can be 100Ufd. @16 volts or more. Increase the 250Ufd. to 1000 Ufd. Both of the small caps could be .047 - a more common value. It would benifit from higher voltage (closer to 12 volts) and batteries with more current capability than the little 9 volt type.

#### aalauzier

##### New Member
Does the TDA2822M amplify a signal in mono or stereo? I found the data sheet and it has multiple inputs that all look the same. Do you have a schematic for making a simple audio amp from and 1/8" jack into 2 speakers? And is there any way to tweak the sound like with the 386 to improve bass response? I also have an amp that i built with 2X386's and added a 1000uf cap instead of the existing 220uf, should there only be a subtle difference or a major one?

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#### audioguru

##### Well-Known Member
The LM386 and TDA2822M work well with a 9V supply. Increasing the supply to 12V simply makes them get too hot without increasing the max output power much.

The TDA2822M is a stereo amplifier with two amplifiers in an 8-pins case.
Both amplifiers can be bridged (as shown in the datasheet) for a single amplifier producing 0.9W into 8 ohms at clipping with a 6V supply. Then an output capacitor is not used. The bridged amplifier will get too hot with a 9V supply.
It would be difficult to add bass boost to the amplifier but adding an opamp can do it.

With a 220uF output capacitor the LM386 has a cutoff frequency of 91Hz where the output is half the power of higher frequencies. Frequencies below about 273Hz are reduced.
If the output capacitor is 1000uF then the cutoff frequency is 20Hz and the amplifier is flat down to about 60Hz.
But maybe your "sub-woofer midrange" speakers cannot produce any sound at or below 60Hz.

#### ronv

##### Well-Known Member
If it is loud enough for you before it distorts the only thing you will likely notice is the bass boost.

#### aalauzier

##### New Member
Thank you ronv and Audioguru, although i sometimes have a hard time understanding AG, the help is always welcomed. I am new to electronics and have had too teech myself through a book, experiments, and youtube, so I may not fully understand what you are saying, but i understand the gist of it. Thank you

#### Bhabyboii

##### New Member
Bass Amplifier

that circuit was worked good ??

#### Bhabyboii

##### New Member
Bass Amplifier

hey guys, do have any 12volts bass booster??
can give me some circuit?
i need it now.

#### audioguru

##### Well-Known Member
The circuit does not boost anything. The bass sounds like it is boosted because the circuit simply attenuates high frequencies.

If your amplifier produces 20W just before clipping then its maximum bass power is 20W and the maximum high frequency power is only 5W. Then the bass sounds louder than the higher frequencies but nothing is boosted.

Here is an extremely simple circuit that attenuates higher frequencies so it sounds like the bass is boosted:

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