Measuring watts out of 3886.

Status
Not open for further replies.
Is it possible to measure the wattage output of an amplifier? Basically, I would like to see exactly how much power my LM3886 amp puts out. I would like to measure it with my DMM, and cannot detach the speaker (it is used in a subwoofer and the speaker is soldered to the output wires). Do I need special equipment, or can I build an attachment to use for my DMM?
 
Hi Mike

Yes, is it indeed possible to measure the wattage out of an amplifier.

You need:

A sinus input (like 1 khz from a CD)
A dummy-load with a known R (typically 4 or 8 ohms)
A scope.

You need the scope to see when your amplifier is clipping. On a good scope you can also measure the voltage accros your load, that you need to calculate the wattage.

In your case it will be very difficult to measure the wattage unless you know the impedance of your speaker at your testfrequency.

Just remeber that the actual wattage is not that important. You will most likely not be able to hear the differnece between having 30 or 40 W.
More is always better regarding clipping/distortion.

When you double your output, say from 50 to 100 W you only get 3 dB more out of your speaker..............................

You could make a teoretical calculation of your wattage........

Thomas😉
 
Thomas,

I do have a scope. it is an old one given to me, with a CRT, and I don't know too much about it. All i know is that it works. As I said, it is being used for a subwoofer. I cannot detach the speaker due to the way it is mounted. It is a 4-ohm 10 inch Lightning Audio car subwoofer, P1.10.4 There is a crossover in it, and I run it from the headphone out of my reciever (it doesn't have a sub out). Can I use a speaker, or do I need a resistor?

Thanks, Mike
 
Thomas, one more thing. The reason I really asked this question is because of the excessive distortion I get from the amplifier. I just am not as satisfied as I feel I should with how much power I get into it from a chip that is supposed to put out 68W, which should be plenty to run a sub. This makes me think that It isn't getting enough power. I know the voltage, +24, 0, -24 is plenty, but the transformer I use was just a cheap one that I got for $3 at a surplus store. What I suspect is that there isn't enough amperage. Would low amperage be a cause for distortion? I know the power output is below 4amps, since that is the max rating on my rectifier. Comparing it in size to a 25VCT 1 amp, it is about twice the size, so I assume that it puts out about 1 amp also. I tried to measure it by connecting my DMM between gnd and the positive of one cap, but got only a small rating when power is switched off (about .6A) but when it is operating, I get 0. This is with the amplifier connected to it.

What amperage is needed for this amplifier to put out all the power possible? Can I purchase another one of the transformers I have now and connect them in parallel (connect the two input wires together and the three output ones together) to get twice the amperage? Or won't this fix anything? Finally, if the power goes over the max rating of the rectifier of 4A, what will happen?

Thanks again for all of the help, Mike
 
Check the voltage on both sides of the output legs of your trans.They should be near equal.

that is why i wind my traffo secondary windings biffiliar, to exactly locate the center tap...

soundnerd,
if you want to do it with the speaker load connected, you can hook up a wattmeter to you ac line and measure the power with audio signals, this will be pretty average, you can determine then, your consumption at various listening levels, what you'll measure though is the entire system, you can estimate losses for the tranformer, the rectifier and finally for the chip, then you will have the music power output...after you subtracted these losses...
 
Status
Not open for further replies.