Amplifier, impedance and power?

What you want is a complex answer. Many of these consumer amplifiers are not properly rated at their output.

The spec you mentioned may be for the both channels, or is it for one channel?

Is it for one channel at a time, or both driven together?

Is this spec the power input of the output stage, or the actual sinewave output to the speaker terminals, in consideration of one of the first two questions?

Is the rating for the full bandwidth of the audio output response, or is it at any one frequency?

I can see by your question, the spec you have is very abartuary, and does not really mean very much.

To have 60 Watts at 8 ohms from one channel, the voltage output would be a bit over 20 Volts of signal RMS. To have 1/2 the power at 8 ohms, the voltage would be about 15 Volts.

Obviously there has to be some type of inverter inside the amplifier, because the drive voltage to the output stage would have to be of the peak-to-peak value that is much greater than the RMS value. Then there is the deficiency loss.

Your best bet is to put a 10 amp fuse on the amp for testing, play it at a fairly high volume (not distorted), and have a DC amp meter in series with the fuse at the same time. Observe the amp reading, and add about 10% to the average that you get. The value you come up with should be very close to the fuse you want to use. If the amp is good, and the 10 amp fuse blows, then put a bigger one to test. If the fuse blows at a low volume setting, or with the volume turned down, then the amp is defective.

If you want to know the true output of your amp, you will need the proper setup with a dummy load, scope, true RMS meter, distortion analyser, and an audio generator. With these tools, and someone who is experienced at it, the true specifications of your amplifier can be detrmined. To do this on the bench, a very big power supply will be required. These draw a lot of current when working.

Jerry G. ======

What is the brand and model number of your amp?

or a bridge type output?

Company: TOA Model: CA-60

On thursday, their web site was not working and I did take the time to find the needed spec. I have now the extra specifications: Current consumption: less than 11.5A at maximum. Therefore, I plan to have a 12A fuse to protect the amp. It is a one channel amp plugged in a 12VDC car lighter. After verification, the car lighter can provide 12A.

Frequency response: 300HZ to 10KHZ, + - 3db

Those two questions remain: How much power will be delivered to the speaker if: The load is 8 ohm impedance The load is 4 ohm impedance

For one speaker, what is the minimum speaker power in watt I should buy? About that question, in the meanwhile, I will try to understand the concept of headroom between the power delivered by the amp and the power available by the speaker(s).

I hope this drawing in easier to read:

Amplifier Speaker Internal Load Impedance Impedance + --------/\/\/\/\/\/---------------------| | | \ How much ** Amplifier / power here? Voltage \ / \ | | - ----------------------------------------|

Hi,

Power = Ueff²/Z Ueff=Umax/SQRT(2)

So if you don't have switching power in your car amplifier (the most time). e.g. Umax = 12V Z= 8ohms Ueff=12/1.4142=8.48 P=9Weff Snort ! With 4 ohms you can have 18Wattts output.

To REALLY have 60W output in a 8 Ohms loudspeaker, you need theorically 31V.

François KNOFF

"Jean" a écrit dans le message de news: snipped-for-privacy@posting.google.com...

This used to be a correct answer. Yet, today we have 'bridged or H-mode' and 'Class D' :-)