Understanding Amp rating numbers.....

[champ04]

I'm a little lost and, frankly, I'm not sure what question to ask.
So let me describe what has me stumped and hopefully either someone can explain it here or point to a place where is has already adequately been described.
Thank you.

My amp has the following numbers associated with it:
300W @ 8ohms
1.5V input sensitivity
26dB gain.

However.....
Using Ohms laws 300W @ 8ohms is ~49Volts
49Volts, according to "dB=20 * log(V1 / V2)" and using the specified 1.5V input sensitivity, is equal to ~30dB gain.
This is pretty significantly larger than the specified 26dB.

Working the opposite direction, starting with 1.5V and 26dB gain leaves me with 112W @ 8omhs.

So maybe 300W is "peak"????

Am I not understanding something?
Or, perhaps the company is being conservative/liberal with at least one of these units. If this is possible, which one is most likely not entirely accurate?

Thanks again!!!

 

[h_a]

So maybe 300W is "peak"????

Well, there are typically many ways to skin a cat. What full power is is only a matter of definition. A popular definition is the power at which the amp's THD@8R hits a certain value. Some companies use 0.1%, others 1%.

Often numbers are also rounded to marketing compatible format and, last, sometimes simply mistakes happen.

Hannes

 

[east electronics]

let me put you more in the picture ...

beyond definition of terms where one might define the power of his amplifier as he likes either peak power or real power there is also another issue

there is a very good chance that one may say 300w rms at 8ohms load and this also can be measured with the classic approach and that will be 1khz signal at pure resistive load on bench tests and this is also can be achieved with only two couples of transistors in the output

In real life though and when real loads are connected to the amp such is speakers you will realize that the actual amp hasn't got exactly guts for 300 watts ...reason is that VI limiters inside will limit the power and drive of the amp with an aspect to safety and not max power

best option will be to state the brand and model of your amp and forum experts will tell you exactly how much power is usable from your amp and probably proper definition of the output power

kind regards
sakis

 

[ingenieus]

The math seems to be in order, but the numbers do not add up.

Once again, marketing triumphs over engineering!?

 

[jkuetemann]

Calculating using the 300W output as a peak value gets the numbers closer.

300W peak = 150W average power (remember, there is no such thing as RMS power)
sqrt(150W*8ohm)=34.6V RMS
20log(34.6/1.5)=27.3dB gain

 

[champ04]

Once again, marketing triumphs over engineering!?

Often the case, however, highly doubt it in this case. I know the designer to be both honest to a fault and has a particular disdain for the majority of the industry and their way of handling these numbers.
Besides, the amp in question is a B.A.T. Vk-600SE. Massive transformers, 18 capacitors per channel, 24 output devices per channel, etc etc. In direct comparisons with so called kilowatt megabuck amps, it gives up nothing in control and dynamics.

Calculating using the 300W output as a peak value gets the numbers closer.

300W peak = 150W average power (remember, there is no such thing as RMS power)
sqrt(150W*8ohm)=34.6V RMS
20log(34.6/1.5)=27.3dB gain

This may actually be the case. The more I thought about it....
The design of this amp could roughly be described as two amplifiers per channel, each handling one phase, with nothing but the speaker load in between.
So perhaps each phase is 1.5V sensitivity/ 26dB gain but with double the power given the parallel balanced design??? Thoughts?

Also, the "Mono" version of this amp is nothing more than the paralleled inputs/outputs of both channels.
Rated numbers for this instance:
1.5V sensitivity
26dB gain
400W @ 8ohms

Thanks, everyone, for the help. I have a weird way of learning things and this community helps tremendously!