• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

simple amplifier

Status
Not open for further replies.

j.friend

New Member
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
 
Last edited:

j.friend

New Member
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
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
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.
 

j.friend

New Member
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 :)
 

Nigel Goodwin

Super Moderator
Most Helpful Member
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 :)
You can't usually use a battery charger as a PSU - and depending on it's type, it might completely destroy your amplifier.
 

j.friend

New Member
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
 

Attachments

j.friend

New Member
ok.
written on it is M40BA LM 386N-1

i think i fried it when i hooked the 12 V power source up :(
 

audioguru

Well-Known Member
Most Helpful Member
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.
 

Hero999

Banned
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
 

j.friend

New Member
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
 

Hero999

Banned
An LM386 isn't the kind of audio amplifier you'd use if you want real power.

How much power do you want?
 

audioguru

Well-Known Member
Most Helpful Member
hey their

try out the lm386 ic schematic i found on this website
Mini Amplifier with LM386. The LM386 is a low voltage audio power amplifier, simple and easy to build a mini amplifier with only a few components. (7/3/2006)

i have built this and quite versitile and durable. Is pretty loud for 1w.
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.
 

j.friend

New Member
An LM386 isn't the kind of audio amplifier you'd use if you want real power.

How much power do you want?
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 :)
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top