simple amplifier

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j.friend

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I have assembled a simple ampilfier (a kit one from jaycar electronics) and to be honest it sounds like crap. It distrots the sound horribly and is very scratchy.

In the instructions it is not specific as to what power source to use, so i used a 9-volt battery. The instructions describe one of the tests as to measure the voltage over certain parts, whilst the voltage i measured follows the trend (one a basically half of the other), the values are not the same as indicated in the instructions.

I measured 7.6 Volts and 3.75 respectively and the instuctions say they should be 11.4V and 5.7V respectively.

I assume that the amplifier therefore needs a 12V power source (which i don't have at the moment).

Could this be the cause for the wretched results that i get when using it or is it more likely to be a dodgy soldering job or something similar?

thankyou for any help
 
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Ok. Thanks for that. i will try and get the schematic from somewhere.

I have the schematic on an instruction set so i will try to scan it tommorow, or draw it in paint if worst comes to worst
 
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The amplifier probvably uses an amplifier iC. the datasheet for the amplifier IC will show what happens when the power supply voltage is too low.

A 9V alkaline battery that measures only 7.6V is dead. Its voltage probably collapses when the amplifier tries to play anything.
 
yeah... I spoke to a couple of people at school and it definately seems that it is a problem with the input power. Hence a aquired a 12V battery charger and will test it out tonight. Thanks for the help
 
j.friend said:
yeah... I spoke to a couple of people at school and it definately seems that it is a problem with the input power. Hence a aquired a 12V battery charger and will test it out tonight. Thanks for the help
Click to expand...

You can't usually use a battery charger as a PSU - and depending on it's type, it might completely destroy your amplifier.
 
okies... i can't find the schemtaics so I took some photos.

I know they probably aren't the most helpful. If it helps i can annotate with parts and values
 

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The LM386 works fine from a new 9V alkaline battery. If you use 12V then its max output level is almost the same but it gets hot if you play it loud.

It is a small simple amplifier with an output of only 0.45W into an 8 ohm speaker at clipping when its supply is a new 9V alkaline battery. When the battery voltage drops to 6V then the max output drops to 0.2W.

Turn down the volume for it to sound good because its 0.2W to 0.45W of output power is almost nothing. If it is turned up louder then its output will be horribly distorted.

A speaker sounds scratchy (no bass) when it does not have an enclosure designed to match its spec's.
 
What is the value of the capacitor in series with the speaker?

Don't tell me it's only 220:mu:F.

It should be 1000:mu:F for an 8Ω speaker for good bass response.

What's the physical size of the speaker?

Don't tell me it's a 50mm speaker?

You won't get any bass from a miserable 50mm speaker
 
The capacitor in series with the speaker is a 470µF one

In terms of the speaker, it is one of my own design, I was building the amplifier to try and get a little more volume out of it
 
An LM386 isn't the kind of audio amplifier you'd use if you want real power.

How much power do you want?
 
The circuit shown on that website is missing important parts that are shown on the datasheet:
1) The 10 ohm resistor in series with a 0.047 capacitor from the output to ground to stop the IC from oscillating.
2) A supply bypass capacitor of about 10uF.

The datasheet shows a graph of max output voltage and distortion vs output power. With a 9V supply the output is 0.45 Watts into 8 ohms at clipping. Not 1W.
 
Hero999 said:
An LM386 isn't the kind of audio amplifier you'd use if you want real power.

How much power do you want?
Click to expand...

I'm not entirely sure... I am really new to electronics (this was my first project) so I was just rtying to make my speaker a little louder for the demonstration
 
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