small powered amp cuts out

i have a small audio amp from a Cana-Kit. it is the Uk193. it is a 20W Bridged Power Amplifier.
the supply voltage for this unit is stated as
Supply voltage: 12 to 18V DC / 2A
now what i have used is 2 small 9volt batteries (those like duracel that you put in your smoke detector). this amp is hooked up to a small horn/speaker (15W). now when i turn on my MP3player (i.e. ipod) and turn thevolume up, the unit cuts out and does not play music until i turn the volume down. However, when i hooked up my Ghetto blaster or my computer to the audio supply to the amp, i could turn up the volume as loud as i wanted.

However, if i hook this same amp to a 12V car battery i can turn it up very loud when using either the Ghetto or the mp3 player.

what does it sound like is causing the problem.
any info much appreciated.

officework13 said:

i have a small audio amp from a Cana-Kit. it is the Uk193. it is a 20W Bridged Power Amplifier.
the supply voltage for this unit is stated as
Supply voltage: 12 to 18V DC / 2A
now what i have used is 2 small 9volt batteries (those like duracel that you put in your smoke detector). this amp is hooked up to a small horn/speaker (15W). now when i turn on my MP3player (i.e. ipod) and turn thevolume up, the unit cuts out and does not play music until i turn the volume down. However, when i hooked up my Ghetto blaster or my computer to the audio supply to the amp, i could turn up the volume as loud as i wanted.

However, if i hook this same amp to a 12V car battery i can turn it up very loud when using either the Ghetto or the mp3 player.

what does it sound like is causing the problem.
any info much appreciated.

Click to expand...

It's blindingly obvious what the problem is - your tiny batteries can't supply anywhere near enough power.

yes, i thought that may be the case.
however, when just using the tiny batteries, and my laptop or Ghetto (i.e. larger audio source), why does it work then. my limited understanding was that it was just supplying an audio source and the batteries were used to ampliphy the sound.
however, now that i think about this, i suspect it works like the following (in is most simplest form):
the laptop sound that is output has more output power/energy and so it requires less power to ampliphy to a higher level enabling a higher sound to come out of the speaker.
so to say the output of the Laptop is 5 units and the output of the mp3 player is 2 units. then to reach a sound level of 10 units i would only need to ampliphy the laptop 2x where as the mp3 player 5x (which my current powersource can not achieve).
i already have an alternative battery source available.

thanks

PS. as for the audio source what is the measure of units coming from the laptop or mp3 player. is there a way to measure this.

thanks

The Cana-kit provides 20 Whats (music power) to a 4 ohm speaker when the supply voltage is 18VDC. Its output is only 14 Watts at clipping with a 13.8V supply.
The current at 13.8V is about 2A.
Your horn speaker is probably 8 ohms so the output power and supply current are halved.

But little 9V alkaline batteries have a max output current of 1A for a few seconds and with a 400mA continuous load the voltage permanently drops to less than 7V in 15 minutes.

officework13 said:

PS. as for the audio source what is the measure of units coming from the laptop or mp3 player. is there a way to measure this.

Click to expand...

Do you mean the headphone output or line level output?

this addresses 2 responses above.
blue room electronics - i was using the headphone output on both the MP3 and the laptop or ghetto.

audioguru
you are absolutely correct in the info you provided me (yes it is an 8ohm horn).

however, what i do not understand is the following:
why does the unit work on the 2 small batteries when i use the laptop or ghetto (headphone jack), but it does not work when i use the a small mp3 player such as an ipod nano (2gb).

When the small batteries worked then the volume from the amplifier must have been lower than when it failed. Double the power from an amplifier is just a little louder but the current is doubled.

Thanks audioguru.
but perhaps if i give you a few more details you will have an answer that may help me (i think)
-the volume on both the mp3 player & ghetto/laptop through the earphone jacks were set at full volume.
-the volume on the amp was not adjusted and was set at 3/4 volume.
-the 2 batteries were full charge 9v duracel batteries.
-it was used for 10 seconds with the laptop&ghetto and worked
-it was then used with an mp3 player (ipod nano & another one using a AAA battery). it worked for 1-2 seconds and cut out. (i even put 2 new 9v batteries in the amp and the result was the same).

so now back to my original question - why does the unit work on the 2 small batteries when i use the laptop or ghetto (headphone jack), but it does not work when i use the a small mp3 player.

I couldn't find a datasheet for a Duracell 9V rechargeable battery.
The old Energizer one was 7.2V (not 9V) and could supply 100mA for a few minutes. The new one is 8.4V and provides 150mA for a few minutes. Their voltage quickly drops.

Back to the question. They performed differently because their output levels were different. You can barely hear a difference of double the power which is double the current.

sorry audioguru for being simple minded (or perhaps my mind is still on the weekend).
however, i think i am clueing in on what you are saying and so i shall draw my questions on that area.
when you say "They performed differently because their output levels were different. You can barely hear a difference of double the power which is double the current." do you mean that the audio source output of the laptop is much greater than the output of the mp3 player. Such that if in fact the power output is 2x greater you woudl not notice the difference when using a standard set of earphones.

if the above is true, then how could i measure the power output (and what unit of measure is it) of these audio devices.

thanks again.

(to solve my problem, i have obtianed a much larger 12v battery supply to powere the amp) and the size will not be an issue.)