Timeline for Not understanding aspects of the LM386 amp
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
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| May 15, 2017 at 15:09 | comment | added | Simon B | @user6186979 If you put things in parallel, then the voltage across them is the same, so the voltage across C3+R1 is the same as the voltage across C2+speaker is the same as the output of the amplifier. "f" is whatever frequency you want to be. The impedance of a capacitor varies with frequency. So a 250uF capacitor has an impedance of 0.63 ohms at 1000Hz, but 6.3 ohms at 100Hz. So actually, if you care about the frequency response at low frequencies, you should increase C2 to lower the impedance. | |
| May 15, 2017 at 13:35 | comment | added | Student | @SimonB Wont the voltage from port 5 however drop slightly over C1 R1 and C2? I just dont get how C2 can be ignored is what i mean? Also for these capacitors, what is f for each? | |
| May 15, 2017 at 13:28 | comment | added | Simon B | @user6186979 (I think you meant C3, R1 and C2). C3 and R1 are in parallel with the speaker, so have no effect on the voltage. C2 has negligible impedance at normal audio frequencies, and can generally be ignored. The impedance of a capacitor at any given frequency is given by 1/(2πfC), where π is pi, f is the frequency, and C is the capacitance in Farads. | |
| May 15, 2017 at 12:06 | comment | added | Student | @SimonB Thanks How would i find the voltage across the speaker, taking into account the impedances of C1 R1 and C2? Since it wont be exactly the same as the output of the amp? | |
| May 15, 2017 at 11:44 | comment | added | Simon B | @user6186979 Unless you have a good reason to do otherwise, use the recommended ones from the data sheet. | |
| May 15, 2017 at 11:39 | comment | added | Student | @SimonB thanks. How would i find the values for C3 R1 and C2 then? Or do i just use the standard values that the datasheet for a 20 gain shows? | |
| May 15, 2017 at 11:36 | comment | added | Simon B | @user6186979 The best place would be before the amplifier. Putting it after would effectively be shorting out the amplifier output at high frequencies, which would waste power and might even damage the amplifier. | |
| May 15, 2017 at 11:33 | comment | added | Student | Thanks for answering, i just have a quick question. With using this amp if i needed to cutoff frequencies above say 15Khz , could i add a lowpass filter before the input? Or would i have to put, the lowpass after the C2 cap? If i am right about THE location to place it, when calculating the cutoff frequencies would i have to take in the other impedances such as R1 C2 and C3, to get the cutoff freq? | |
| May 15, 2017 at 11:22 | history | answered | Olin Lathrop | CC BY-SA 3.0 |