Bass boost with LM386

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,372
I'm using a LM386 amplifier to drive a 2 1/2 inch loudspeaker, and I wan't it to have a 3dB bass "booster" (works more like a trebble atenuator). The frequency is about the same, so in the RC circuit (from pin 5 to 1) I'm using a 33nF cap as sugested. But I will use a 39K to have an atenuation of about 2.8dB (15K is sugested in the NS datasheet for a 6dB attenuation). Am I doing the calcutations correctly?

Also I tested the 6dB bass boost with a cheap 3 inch speaker but that sounded abusive to me :confused: (loss of detail comparing with no boost at all). Is it ok to use a 3dB bass boost with a smaller (2 1/2 inch) speaker?

I already know that the high frequencies will be limited, but with the minimum gain the amplifier is already saturated at the maximum volume.

Datasheet: http://www.national.com/ds/LM/LM386.pdf
 

Solcar

Joined Jun 8, 2007
21
I agree that increasing the resistor lowers the bass boost amount. Yet it also shifts it to a lower range. I think you will tend to want to do more the opposite--roll off the lowest end because the speaker can't do any useful reproduction down there and will just distort trying.
 

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,372
No, I really want to atenuate the high frequencies (the term "bass boost" does not apply very well). A 2-1/2 inch speaker will atenuate low frequencies by nature, since it barely reproduces bass. But I don't want to atenuate severely (just a 3dB "boost", or atenuation).
 

Gadget

Joined Jan 10, 2006
614
For bass I'd be using a chunkier amp, as thats the bit of the spectrum that you have to pump most of the power into.
 

Thread Starter

bloguetronica

Joined Apr 27, 2007
1,372
For bass I'd be using a chunkier amp, as thats the bit of the spectrum that you have to pump most of the power into.
The LM358 is the one that allows supply using batteries. That's the reason I chose it, amongst others.

Nevertheless, since we are talking about chunkier amps, I heard that the TDA2003 is lousy (I mean, I hardly heard no noise using the LM358 and my excellent s*ny headphones, not to make publicity), and the TDA2003 has a little less noise reprodution. Did those guys exagerated on gain (100 in the example circuit, which is abusive)?

I think I can reduce the gain by using a different relation in the resistors of the negative feedback circuit for TDA2003. Would this reduce noise and gain (more negative feedback, lesser gain, but a better amp)? Nevertheless, a gain of 30 is enought.
 
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