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i was working on an lm386 audio amp for my tv, but it keeps buzzing. here is the schematic i used. **broken link removed** does anyone have a better one?
I am still having some trouble with pin, 3. I know it has been explained to me but i am clearly missing something here. I see a 10k resistor connected from ground to pin 3. but that is not correct and does not seem to work, Im very new at this and I realize it is a very basic thing, but again I can not seem to get it right. can someone please dumb this down for me, obviously i need it. If i connect a 10k audio taper pot to this it again does not seem to work? Audioguru you said it is a slider but i am not sure as to what you mean by this?
The resistor connected to Vin, pin 3 and ground is the volume control input. The resistor is a potentiometer (pot) with three (3) terminals. At Vin the signal is applied and developed across the resistor/pot from Vin to ground. The signal is tapped by the wiper of the pot and applied to pin 3. The pot acts as a voltage divider.
For the moment, consider the input impedance at pin 3 as infinite. If the pot were 10k and the wiper set at the midpoint of the resistance, there would be 5k on one side and 5k on the other. With a 2V signal at Vin, 1V would be developed across one half and 1V developed across the other, which would present a 1V signal at the amp's input. Adjusting the wiper toward ground would reduce the input to the amp, and with the wiper adjusted all the way to ground potential, zero input to the amp.
Just jumping in here because I speak newbie, being one.
Google "potentiometer" (sans quotes), click to look at images, and all will become clear, or at least it will help.
When you turn the TV volume up or down, you twist a knob. But behind the knob is a potentiometer (pot). It's a resistor with a sliding contact, the "slider" audioguru speaks of.
The sliding contact is always the center solder terminal of a pot, and this is what you'd connect to terminal 3 of the LM386 in the schematic (circuit diagram).
The two outside terminals of a pot are, in fact, simply a resistor. You connect one of these to ground and one to Vin, as in the schematic. It makes no difference which outside terminal connects to what, they're still just the ends of a resistor.
(it would matter which outside terminal connected to what with a "log pot," or "audio taper pot," but those are not the issue here, google if you like.)
I am getting alot of feed back and distortion when I connect the Potentiometer to ground as well as connecting the 10k capacitor between pin 1 and pin 8. Is there any way to reduce the amount of feedback and distortion? This is happening before the oscillator is connected to the amplifier, just to clarify
Why are you connecting an oscillator to the input of the power amplifier?
Why are you connecting a capacitor from pin 1 to pin 8 which increses the gain 10 times?
Why do you connect the volume control wrong?
if i knew how to do this i wouldnt be posting the questions on electro-tech online.com
here is the project, create an oscillator that produces square waves
connect oscillator to 16 step sequencer
inorder to hear oscillators awesome squarewaves I need to make an audio amplifer which is what I am doing. I made a 741 but in another post you said
"A 741 is an old opamp that cannot drive a speaker.
An LM386 is a good little power amp that drives a speaker very well if the simple circuit is made like shown in its datasheet.
But many LM386 amp projects on the internet have missing parts that make them perform poorly."
so here we are, making an lm386 well...trying too and having alot of trouble doing so.
This is the schematic I am using, which is in the datasheet. According to this schematic a 10uf capacitor is to connect pins 1 and 8, secondly I asked how to connect the POT to pin 3 and was instructed on the previous page of this thread, that one terminal goes to ground one goes to Volts and the middle is connected to pin 3, this is how i preceived the instructions.
The potentiometer does not connect to "Volts." That is, it doesn't connect to the power supply. Vin is signal in, not volts in, "signal" being the square wave that you want to amplify.
Explanation: Vin means signal (input), while Vs or Vcc means power supply.
So one side terminal of the pot connects to ground, the other side terminal then becomes Vin and connects to your square wave generator (oscillator), and the center terminal connects to pin 3 of the LM386. Thus you turn the pot to vary the input to the LM386 from zero/ground to maximum.
Probably correcting the Vin connection will solve your present distortion/feedback problems. But...
<< a lot of feed back and distortion when I connect the Potentiometer to ground as well as connecting the 10k capacitor between pin 1 and pin 8...This is happening before the oscillator is connected to the amplifier... >>
As audioguru points out, the capacitor between pins 1 and 8 increases the gain of the LM386. No capacitor, the gain is 20. Capacitor added, the gain jumps to 200, which is a big jump. Too much gain could cause both distortion and feedback, so remove the capacitor (but first correct the Vin connection of the pot).
Explanation: Gain and volume are not the same thing, but you could think of them as the same in this (only this) case. If this were an audio amplifier then the capacitor between pins 1 and 8 would set the total output power available (20 or 200), and the pot would set the listening level (However, the "20 or 200" is not watts, or output power, or something else: it's gain).
All of which bring us to a pretty big confusion. Editing your statement for clarity:
<< a lot of feed back and distortion...This is happening before the oscillator is connected to the amplifier... >>
This is confusing because it's impossible as stated. "Feedback" is, by definition, an amplifier's output becoming its input, so the amplifier runs wild, infinitely amplifying its own input until things break. But if there is no input--the oscillator is not connected--then there can be no feedback.
Also, distortion, by definition, occurs in an amplifier (in this case). But if there is no input--the oscillator is not connected--then there's nothing to distort.
However, I think this is a confusion in use of technical terms, and the problem is again the wrong Vin connection. If the power supply were connected to the amplifier input (as it apparently now is), then the LM386 would be trying to amplify its own power supply, which would certainly cause some strange things to happen. Again, correcting the Vin connection would fix this.
Sadly, connecting the power supply to the amplifier input (Vin) might have burnt something out, you might have to build another LM386 amplifier. Or maybe not, of course. We hope for the best.
I'm making this a separate post so as not to confuse things (I hope).
There's another issue with the now-infamous Vin connection. Specifically: how to connect the oscillator output to the LM381 amplifier input (Vin).
Bottom line: simply using a piece of wire might not be so hot. Use a capacitor, maybe a .1uF. One terminal (lead/wire) of the capacitor connects to one of the side terminals of the pot (Vin), the other terminal connects to the oscillator output.
The other side of the pot still connects to ground, the center terminal still connects to pin 3 of the LM381.
Explanation: The oscillator and amplifier are different units with different power supplies (I assume). Simply connecting them together with a piece of wire can cause one power supply to affect the other with unknown results. There are also possible issues with bias that are so complicated the only thing we can do is ignore them.
Using a capacitor for the connection will eliminate any DC interaction between the units (capacitors pass AC but block DC, generally), and might at least minimize any bias problems.
I say "capacitors pass AC," but actually they pass changes in voltage. A capacitor will pass your square wave, feeding the amplifier what amounts to a pure AC signal, which is what it wants.
I suggest a .1uF (point-one microfarad) capacitor simply because that value is commonly used with audio frequencies. Others might have a better idea. Be sure the voltage rating of the capacitor is higher than your power supply voltage.
I wish you continued your thread about the oscillator.
The oscillator and the LM386 power amplifier were missing important supply bypass capacitors.
The oscillator had a very high output level and your LM386 power amplifier had a gain that was much too high.
The oscillator had DC on its outout that must be blocked with a coupling capacitor.
is it possible to have more than one input, i guess i'd have to make a mixer of sorts to do that? can i use a dual op amp as a crude mixer? the more inputs the better
We forgot to tell you that the ground of the oscillator circuit must connect to the ground of the amplifier. Usually the shielded audio cable between them connects the two grounds together.
A simple mixer can be made from two resistors feeding the volume control. One resistor from the oscillator and the other resistor from the other input. If you use 10k resistors and a 10k volume control then the resistors reduce the input signal to the amplifier a little.
A single inverting opamp is an excellent mixer. It can have many inputs. Each input can have its own volume control.
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