Capacitance across an audio signal

In summary, Changing the 250uF cap to a larger one, such as a 330uF or 470uF, would affect the audio signal by making it quieter and possibly improving the audio quality. It would also further smooth out the waveform and lower the cut-off frequency, potentially increasing the bass output. However, the exact cap size needed may depend on the desired bass levels and the impedance of the speaker.
  • #1
Packocrayons
49
0
Looking at this datasheet:
http://www.ti.com/lit/ds/symlink/lm386.pdf
Most circuits near the bottom have a 250uF cap in line with the output.
Would changing this cap affect the audio signal or would it just further smooth out the waveform?
 
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  • #2
Packocrayons said:
Looking at this datasheet:
http://www.ti.com/lit/ds/symlink/lm386.pdf
Most circuits near the bottom have a 250uF cap in line with the output.
Would changing this cap affect the audio signal or would it just further smooth out the waveform?

Just took a very quick look. I think if you were to make the signal smoother then you are effectively attenuating the AC content of the signal, so if you were to increase the cap size then the audio would become quieter.

If you wanted to improve the audio quality replace the cap with a polypropylene or polyester type one.
 
  • #3
I don't really have access to polypropylene/ polyester caps.
I'm just wondering how accurate I have to be with the cap size.
 
  • #4
Packocrayons said:
Looking at this datasheet:
http://www.ti.com/lit/ds/symlink/lm386.pdf
Most circuits near the bottom have a 250uF cap in line with the output.
Would changing this cap affect the audio signal or would it just further smooth out the waveform?

That is a DC blocking cap, since the opamp is being run off of a single power supply voltage (instead of split power supplies symmetric about ground). It needs to be big enough to pass the lower frequencies in your audio signal.

You would calculate the value of the capacitor based on the lowest passband frequency and the impedance of the load (like the speaker).
 
  • #5
Alright, I'm just having trouble finding a 250uF, I'm looking at abra electronics (already ordering from there) and the don't seem to have one in any type.
 
  • #6
Packocrayons said:
Alright, I'm just having trouble finding a 250uF, I'm looking at abra electronics (already ordering from there) and the don't seem to have one in any type.

You can certainly go to the next biggest size. Use a 330uF or 470uF with a voltage rating that is at least twice the amp's power supply voltage.
 
  • #7
Oh, and be sure to place it with the polarity correct -- the + side faces the amp, and the - side faces the ground-referenced load.
 
  • #8
I figured that with the polarity.
I'll try to get as close as I can while staying above,
Thanks.
 
  • #9
If you look at the -3db cut off assuming 8Ω speaker

[tex] f=\frac 1 { 2πRC}\;=\; 80Hz[/tex]

If you need to get more bass, you should use bigger cap. A 470uF will bring the cut off freq down to about 40Hz.
 
  • #10
Sounds good, I'm going to be looking for a more bassy (bassish?) sound, 470 will be perfect.
 
  • #11
yungman said:
If you look at the -3db cut off assuming 8Ω speaker

[tex] f=\frac 1 { 2πRC}\;=\; 80Hz[/tex]

If you need to get more bass, you should use bigger cap. A 470uF will bring the cut off freq down to about 40Hz.
They probably chose 250uF to get the cut-off above 60Hz in order to minimize the "60(or 50)hz hum" picked up from stray a.c. power lines. The 330uF cap would put the -3db cut off right at 60Hz.

With the 470, the OP may get a little more "bassy (bassish?)" than he wants. :biggrin:
 
  • #12
Bass is good, if your speaker is still intact (and not burnt out), there isn't enough. :D
 

What is capacitance across an audio signal?

Capacitance across an audio signal refers to the amount of capacitance present in a circuit that is carrying an audio signal. Capacitance is the ability of a capacitor to store an electrical charge, and it can affect the flow of current in an audio signal.

Why is capacitance across an audio signal important?

Capacitance across an audio signal is important because it can have a significant impact on the quality of the audio signal. Too much or too little capacitance can result in distortion, noise, or loss of signal. Therefore, it is important to understand and control capacitance in audio circuits.

What factors affect capacitance across an audio signal?

The two main factors that affect capacitance across an audio signal are the physical properties of the materials involved in the circuit and the frequency of the audio signal. The type and size of the capacitor, the length and material of the wires, and the distance between components can all impact capacitance.

How can capacitance across an audio signal be measured?

Capacitance across an audio signal can be measured using a multimeter or an oscilloscope. A multimeter can provide a direct measurement of capacitance, while an oscilloscope can measure the voltage across the capacitor and calculate the capacitance using the known frequency of the audio signal.

How can capacitance across an audio signal be controlled?

Capacitance across an audio signal can be controlled by using the appropriate type and size of capacitor for the circuit, keeping the length of wires and distance between components as short as possible, and using shielding to minimize interference. Careful circuit design and layout can also help to control capacitance and improve the quality of the audio signal.

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