What is a good formula???

[HAL9000]

I've essembled a dummyload for my repaired amplifiers.

and i was wondering what a good formula is.

I have a 8ohm dummyload.

I now do the P=U.I formula or

P=I (2) R
I measure the I and the U separate.
is this okee what i'm doing???
To get the full RMS power.

i hope to hear something :thmbsp:

 

[jstang]

Sample below with Volts Peak. What you using to measure the voltage?



Vrms = Vpeak * .707 = 50Vp * .707 = 35.35 Vrms

Power RMS = Vrms * Vrms / Ohm = 35.35 * 35.35 / 8 = 156 RMS Watts.


jk

 

[HAL9000]

Sample below with Volts Peak. What you using to measure the voltage?



Vrms = Vpeak * .707 = 50Vp * .707 = 35.35 Vrms

Power RMS = Vrms * Vrms / Ohm = 35.35 * 35.35 / 8 = 156 RMS Watts.


jk

i measure with a voltage meter and a Ampere meter.
you calculation is for scopes peak to peak measurement.
V rms is indeed Upeak/1.41= X (X*X)/(dummyload Resistance)

i do not use a scope to measure the voltage .

I use the scope to see when the amp is starting to clip.

 

[Turbokeu]

I've essembled a dummyload for my repaired amplifiers.

and i was wondering what a good formula is.

I have a 8ohm dummyload.

I now do the P=U.I formula or

P=I (2) R
I measure the I and the U separate.
is this okee what i'm doing???
To get the full RMS power.

i hope to hear something :thmbsp:

Some months ago I made a double 8 Ohm dummy load too from 8 pieces of 2 Ohm/50W/1% power resistors (2 times 4 x 2 Ohm in series = 2 x 8 Ohm/200W), mounted with thermal paste onto a big 20x14x4cm heatsink.

To make accurate AC voltage or current readings in the audio range (let's say from 20Hz to 20KHz) I use my true RMS Fluke 187 multimeter (common price is in the 500 Euro range).

Anyway you don't need to measure current: P = U²/R
Where R=8 Ohm and U the measured RMS voltage over the dummy load.
You can double check the measured voltage with the scope (needed anyway to monitor clipping): For RMS: measure the peak to peak voltage on the screen, divide by 2, and then divide by sqr2.

CD

 

[jstang]

Using a meter, how can you tell the exact point ( gain / volume setting ) that clipping of the signal starts?

I mean, how will a meter indicate that the test signal is now starting to clip by even the smallest amount?

jk

 

[Turbokeu]

Simply not.

Even with a scope the signal can have several % of clipping before you can see it...

Edit: I meant that it is not possible with a normal multimeter.
Real distortionmeters measure the difference between the input signal and the output signal of the amplifier and display it in percent.

CD

 

[jstang]

Simply not.

Even with a scope the signal can have several % of clipping before you can see it...

Edit: I meant that it is not possible with a normal multimeter.
Real distortionmeters measure the difference between the input signal and the output signal of the amplifier and display it in percent.

CD

I know I have to raise and low the volume value several times to see the point at which it starts to clip on a scope. As you mention that can be off by a fair amount. I just picked up a distortion meter for the basement.

jk