Limitation of current !!

[Mukhalled]

hi friends 
I've built an audio amp ( I chose two projects , volume controller and power amp) and they work together pretty good but when I increase the volume (almost max) I hear very bad sound (distorsion). I've used many loudspeakers from the smallest to the largest but it is the same distorsion all the time.  ???

So what do you think the problem is? I've heard about "limitation of current" ...  ???
here are the projects i've built:

http://www.electronics-lab.com/projects/audio/039/index.html
http://www.electronics-lab.com/projects/audio/006/index.html

Please can you suggest something to do...  ;D

 

[heathtech]

My guess is that you are driving the amplifier too hard, causing overmodulation. There is no amplifier with infinite gain, so if your signal is driving too hard, the peaks of the signal get chopped and cause distortion.

 

[Mukhalled]

hi heathtech
I think you are right, thank you for taking time to answer me

 

[audioguru2]

Hi Mukhalled,
Back in February you had high distortion with this project when you turned the bass and volume too high. When the bass is turned up then the amp must produce 16 times more power.

The TDA1554Q amp IC in our project's circuit provides about 5W per channel just below clipping into an 8 ohm speaker, with a 12V supply. It provides about 8W into a 4 ohm speaker. Its 22W rating is with a 4 ohm speaker, a 14.4V supply, at only a single frequency (1kHz) and at a horribly distorted 10% distortion.
My car radio produces about 14W per channel into my 4 ohm speakers (14.0V supply) at just below clipping and has 4 channels for a total of 56W. It plays very loudly in my car and its advertised power output rating is 200W!

7W or 12W isn't much power, maybe you need an amplifier and speakers for much more.
Maybe your supply voltage drops below 12V when the amp is playing loudly. Then your power supply is "limiting the current". The amp's undistorted power output is less with less supply voltage.
Maybe your speakers are distorting since most are rated for "peak" or "maximum" power, which is double their real power rating.

I think your problem is that you are turning up the bass and volume too high for the low-power amplifier.

What is feeding the LM1036 IC? It distorts with an input greater than about 300mV. Maybe you need attenuators from your source to reduce the level to no more than 300mV. ;D

 

[Mukhalled]

hi
first i want to thank you  ;D

The audio source is a (computer CD-player) it sounds strange, isn't it  ;D
I don't know actually how many mV it gives  ???

So I 've to check it out, if more than 300mV then I've to reduce it , right?

Thanks again

 

[audioguru2]

You are welcome, Mukhalled. ;D

I think I know what is your problem.
I have seen cars with naked speakers sitting on the back shelf, with no bass and no enclosures! They have the bass cranked up to max to try and make the speakers sound less tinny.

Speakers must have an enclosure to keep the sound wave behind them from cancelling the sound wave in front of them. The enclosure for a speaker must match it to get good bass. Then you won't have to turn up the bass and the sound will be much louder before distortion.

It is also important for the speakers to be connected with the same phase for good bass.
Try it. Put two speakers facing each other about a couple of cm apart. If they have the same phase then the bass will sound good. Then reverse the two wires on one speaker and the phase will be wrong and the bass will disappear. ;D

 

[Mukhalled]

Hi Audioguru 

Actually I've already connected the speakers with same phase and I hear a very good bass  ;D, I mean if we say, the volume has 10 levels I can hear a great sound (bass & treble are max) from 1 to 8  but the last two levels (when i increase the volume) distortion begins  .

Do you think if I put a small fan on the heatsink it will dicrease the distortion.?!
May the heat cause this problem?

Thank you for taking time to answer me 

 

[audioguru2]

Hi Mukhalled,
You shouldn't have the bass and treble controls at max. Speakers should sound normal with the bass and treble controls centered. There must be something wrong with the speakers or their enclosures for you to need to boost the bass and treble so much.

When the bass and treble controls are max then the amplifier needs to produce 16 times as much power as when they are centered. You hear distortion when the amplifier reaches the limit of its output power with your supply voltage and speaker impedance. So if you turn down the bass and treble to a normal center position then you won't have distortion until a much higher volume.

Maybe your power supply can't supply enough current for the amp and its voltage drops when the amp is playing loudly. Measure its voltage. ;D

 

[Mukhalled]

Hi again Audioguru, Our fantastic expert

 

[audioguru2]

Hi Mukhalled,
I am glad that your audio system doesn't have distortion anymore with the bass and treble controls in their normal centered position. ;D
You can turn them up a little until you hear distortion again.
In your car with the engine running and charging the battery, the voltage is about 14.4V. Adding a 1.5V battery will just kill the added battery quickly, due to the high current.

In order for a sound system to sound twice as loud, the amplifier power must be 10 times as much. You want to turn the bass and treble controls to max then the amplifier power must be 16 times as much. Then you will need amplifiers, heatsinks and powerful speakers to match.

For an amplifier to have 10 times the power, its supply voltage must be slightly more than tripled (3.16 times, the root of ten). Then the supply current will also be slightly more than tripled. Power equals the voltage times the current, you know.

I am glad to help you be ahead of your Audio Tech class next term. ;D

 

[Mukhalled]

I have no more questions  ;D , thanks a lot.

Regards