Need Help With Small Stereo 4W 9V amp

Thread Starter

bubbagump0

Joined Jul 10, 2007
26
I am building some small, portable speakers. I have found some great speakers (8 ohm, 2-4W), but am having a lot of trouble finding a good amp for these speakers. I am planning on powering it with a 9V battery. I am going to be putting the amp and spaekers in a compact space, so I need a very small stereo ampl. I wish I could just design my own amp just for this purpose, but because I am very new with audio, that is not possible. If anyone knows of any amps, kits, schematics, or sites where I could learn to build my own amp, PLEASE inform me.
 

hgmjr

Joined Jan 28, 2005
9,029
Here is a 4W audio amplifier from www.discovercircuits.com that is powered by 8 to 12 volts. If you intend to handle stereo you will need to consider building two such amplifiers.

If you are thinking of using a standard 9V transistor battery, you are going to have difficulty getting any useful life from the batteries.

hgmjr
 

Gadget

Joined Jan 10, 2006
613
Well, using the formula "Vpp squared, over 8R" we can see that the maximum RMS power you can get using 9 volts into 8 ohms using a single ended amp (not taking loss's and VD across semis into account) is a little over 1 watt.
Using a Bridge configuration (2 amplifiers working in opposition across the speaker) 4 x that power ( or 5 watts RMS) would be the max (assuming no loss's) power.

As hgmjr has suggested, a 9v (PP9 style) battery would not hack the pace, and a pack made from AA's or larger would be the bare minimum required to get any usefull life and current delivering ability.
 

Thread Starter

bubbagump0

Joined Jul 10, 2007
26
Well here's the deal. I have a very small space to put these speakers in. Now I can figure out the power source, but the amp is the tough part. I have already looked at ICs, but I cant build my own circuit, so I need a full kit. Also, if I got an amp for say, 8W stereo, then with 9V (forget about battery life problem for now), could it end supplying about 4W to each channel? Can someone please help me find a kit or something? Thanks
 

bloguetronica

Joined Apr 27, 2007
1,359
I think if you want to take maximum power from a small voltage, you should consider using 4 Ohm speakers instead.
 

Thread Starter

bubbagump0

Joined Jul 10, 2007
26
Well, I guess I need an amp with about 2-4W of power, and I can adjust my power supply to fit it. I still need help finding a stereo amplifier kit. Thanks.
 

mhtplsh

Joined Jul 29, 2007
27
Use TDA 2005. It is very well made for 12V supply. Can also be bridged to get more power.
U will find many projects on web of this IC. .
 

nomurphy

Joined Aug 8, 2005
567
The only way to do this efficiently is to use a class-D amp, a switching amp. Check the websites of Maxim, National Semi, and Texas Inst (T.I.) to mention a few.
 

Audioguru

Joined Dec 20, 2007
11,251
An LM386 amplifier IC gives a max output of 450mW at clipping into an 8 ohm speaker with a 9V supply. A little 9V battery will last for a while. When the battery voltage drops to 6V then the max output at clipping is only 200mW.

When a speaker is in a small space then it won't produce any bass frequencies.
 
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