[SOLVED] problem with audio amplifier using ne5532 / LM386 ic

Hi frnds, i want to make an headphone amplifier.I used LM386 ic and built the amplifier.The amplification is good but the only problem that i encountered is noise in the output even when no input is applied.After this i came at conclusion the the ic LM386 is noisy .Due to some reason i am unable to upload the image but the link is given below:
Audio Amplifiers
I have used the very first circuit diagram.
Can anyone suggest me how to reduce the noise in output.
I am running out of time. So guys please suggest me any solution.
Thanx in advance.

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sorry guys ......by mistake i have just entered the wrong subject ....this problem is with LM386.
Also i used NE5532 to make headphone amlifier.In this the noise is almost absent but the amplification is not good. the audio output gets distorted.
the circuit is given below........

In this i made a little bit modification ....instead of using BD139 and BD140 i used BC558 and BC548 transistors.
Guys please help me with any of above circuits .
Thanx.

You have a poor selection of ICs for this task. The noise is bad because you are using the LM386 at high gain and it isn't a particularly low noise device anyway.
The NE5532 is an excellent low noise pre-amplifier but it isn't capable of driving the output transistors. It also has an unusual characteristic of having head-to-tail parallel diodes across it's input pins which limits it's ability to set DC bias conditions in this kind of application.

Using the parts you have, I would remove the capacitor between pins 1 and 8 of the LM386 and then use the NE5532 as a pre-amplifier to increase the overall gain again.

Brian.

Just how much and what kind of noise are we talking about here? It's true that, like betwixt said, the LM386 is not a low-noise device, but it's possible that you experienced a much higher noise level due to other factors. Is it a constant hissing, crackling or humming sound?

Another thing is that the BC558/548 transistors are not good choices for an audio power output stage. They are intended for much lower power levels.

Thanx for ur reply......
With LM386 I am getting a constant hiss type noise even when no input is given and this hiss type noise is still present when the signal is amplified.
now using ic ne5532 i cannot able to amplify the signal .The schematic is shown

Instead of using BC558/548 transistors which transistors u guys suggest me to use.
Is there is any problem with schematic i used with ne5532 coz i cant get good amplification. The oputput is distorted .

Use the BD137/138 or BD139/140 or equivalent medium power transistors for your output stage.
You may find that your output distortion is down to not having sufficient forward biasing of your output transistors which is causing crossover distortion.
Add small value resistors (same value for each) in series with the 2 diodes, D1,2; for a quiescent current of around 25mA through the output transistors.
You might need clip-on heatsinks for your output transistors if their operating temperature rises.

hope this assists
Mik

I doubt the output stage bias is the only problem although I agree the quiescent current will be too low. The NE5532 is not a current output driver, it is intended to be a low level, low noise pre-amp for small signal applications and cannot produce enough current to drive the output transistors directly. As I stated earlier, it has a maximum differential input voltage of 0.6V so it might struggle to establish the center rail voltage.

Arumsharma0731, the hiss is simply because the LM386 is not a low noise device and you are running it with a voltage gain of 200. What you need to do is drop the gain by removing the feedback capacitor so the noise goes away then boost the input signal using the NE5532 as a pre-amplifier. This will give you good power output and low noise at the same time.

Brian.

Thanx for the advice dear BETWIXT..........i hope ur suggestions are helpful to me......but i wanted to use only ne5532 ic .
Do u have any suggestion by which i make NE5532 to drive the output.What if i connect unity gain buffer before driving the output.Is it work??????????

I cast my vote with those who recommend leaving pins 1 & 8 unconnected. This will operate the 386 at a gain of 20. You'll get less noise.

You can also leave pin 7 unconnected (according to my data book).

It's likely your input level is already at a volt or so of amplitude. If that's the case then you don't need voltage amplification so much. The purpose of the 386 is to give you current gain. Which is to say, low output impedance.

The 5532 does not have low output impedance. It's more useful for low-noise voltage gain. You can use it as a pre-amp in case your input is less than a tenth of a volt in amplitude. That's when you need voltage gain.

Re: "....but i wanted to use only ne5532 ic .
Do u have any suggestion by which i make NE5532 to drive the output."

The NE5532's have more than enough available output current for driving your current follower, the datasheet for them is here:
NE5532 Datasheet pdf - Dual Operational Amplifier - Fairchild Semiconductor
You will see from the output current limiting graph that you can in fact easily drive a 600ohm load from them to full output swing.
Regarding the 0.6 volt input, this is when the input current is at 10mA - very unlikely you will be anywhere near this with the circuit you have shown.

hope this assists
Mik

thanx for ur support guys...........now i am able to reduce the hiss type noise at the output by just removing the 10uf cap between pins 1 and 8.There is still a little bit of hiss noise at the output but for me that is ok.
Now the headphone amplifier i designed using LM386 is MONO but i wanted to make it in STEREO.So i just decided to use same for circuit for both LEFT & RIGHT outputs having 2 separate inputs(Left and Right).The problem is that how can i control the output volume level by just using only 1 pot of 100K.The circuit is shown below.......

Hope u all assist me with this also.
Thanx in advance.

I suggest that you use a dual pot. To use a single pot, you'll have to include some extra circuits to translate the movement of the single pot to two channels. It's possible, but in my opinion, it's not worth the hassle for such a simple amplifier.

By the way, I also suggest that you change the output coupling cap from 100uF to at least 220uF, preferably more. With an 8-ohm load, 100uF will give a -3db low frequency cut-off at 200 Hz. If you intend to listen to music with a reasonably good headphone, roll off at 200Hz will result in poor bass reproduction.