RMS wats to watts

spuffock · Mar 29, 2004

Nigel,didn't we used to put up with enormous distortion figures, once?
Weren't some of the old valve am radios with single ended outputs quoted as 3watts @ 7% thd? And we listened happily to them?
Or has my memory dropped a decimal?

Nigel Goodwin · Mar 29, 2004

spuffock said:
Nigel,didn't we used to put up with enormous distortion figures, once?
Weren't some of the old valve am radios with single ended outputs quoted as 3watts @ 7% thd? And we listened happily to them?
Or has my memory dropped a decimal?

Yes we did, but there wasn't any choice!. Many valve radios and amplifiers worked with no negative feedback, so the distortion figures were pretty horrible - but so is AM anyway

Even now, valve amplifiers are popular with guitarists, basically for the distortion they give - which for lead guitar gives them the sound they want. What really bugs me is the extortionate prices they charge for a lot of 'valve' gear - particularly for preamps! - add a single ECC83 and charge £200-300 more!. A friend at work has a Trace Elliott preamp/power amp which proudly proclaims 'Valve preamp' on the front - they even stick the valve outside the main casing so you can see it!.

I would point out he didn't buy it for the valve, he bought it because it was going cheap.

Styx · Mar 29, 2004

ljcox said:
Styx said:

Err true VA (or Volt-Amps) and Watts are the same units.

Click to expand...

This statement is only true if the phase angle is zero!

Volt Amp is called "Apparent Power" since it is simply the current multiplied by the voltage (assuming an AC sinewave source).
The actual power is the energy consumed by the load per second.
Actual Power = Apparent Power * cos(theta) where theta is the phase angle.

Len

I think you need to go back and look at this...

VA has EXACTLY the same units as watt's

what you are talking abt is the power factor that is COS(theta) bu tthat is a unitless scaling factor

V*A*Cos(theta) still has the units VA or WATTS

spuffock · Mar 29, 2004

On the subject of guitar amplifiers, I won't mention the make, but there is a current model which sports an ECC83. A corner of the PCB sports a block of wirewound resistors to drop the transistor output supply rail to run the heater. The electrode voltages are all 0v!! Removing the valve has no effect on the performance of the unit. I have tried to obtain a circuit diagram from the manufacturers with negative results. But it DOES produce the output power specified.

ljcox · Mar 29, 2004

Styx said:
ljcox said:

Styx said:

Err true VA (or Volt-Amps) and Watts are the same units.

Click to expand...

This statement is only true if the phase angle is zero!

Volt Amp is called "Apparent Power" since it is simply the current multiplied by the voltage (assuming an AC sinewave source).
The actual power is the energy consumed by the load per second.
Actual Power = Apparent Power * cos(theta) where theta is the phase angle.

Len

Click to expand...

I think you need to go back and look at this...

VA has EXACTLY the same units as watt's

what you are talking abt is the power factor that is COS(theta) bu tthat is a unitless scaling factor

V*A*Cos(theta) still has the units VA or WATTS

Yes they have the same dimensions (or units to use your term) but that is not the point I was trying to make.

I was pointing out that Apparent power and Actual power are not necessarily the same (unless Theta = 0) and are related by cos(Theta)

Len

Painandsuffering · Apr 12, 2004

Re: Watts RMS

pike said:
Painandsuffering said:

Really quick question... Why can't he just convert watts rms to watts peak which is as simple as multiplying his watts rms by 1.414 or dividing his watts rms by .707

Click to expand...

i believe you divide by 1.414 not .707

As for the RMS ratings and stuff, dont let the watts suck you into buying an expensive rip off. I bought a $300 US amplifier, rated at 600 watts, when i looked around for the RMS rating i found out it was about 300 watts.

When i took it home to test it out, i found out it was 300 watts RMS at 10% THD. you heard right 10% THD !!!

No actually it is multiply by 1.414 or divide by .707 because in order to get rms from peak you multiply..... peak*.707=RMS.....Rms/.707=peak!

blogGreen88 · May 1, 2006

car stereo

Are you talking about car stereo or something else?! Umm. There is a good page for car stereo perhaps!
Also,you can find some other content on it,such as ceiling lights or dlp projector or las vegas home.
You can search on the homepage try some other keywords,no ads even.these page updated every day.Because of the huge database,it perhaps not very fast,if you don't like it,take it easy.

Roff · May 1, 2006

Re: car stereo

blogGreen88 said:
Are you talking about car stereo or something else?! Umm. There is a good page for car stereo perhaps!
Also,you can find some other content on it,such as ceiling lights or dlp projector or las vegas home.
You can search on the homepage try some other keywords,no ads even.these page updated every day.Because of the huge database,it perhaps not very fast,if you don't like it,take it easy.

Do you get paid to post a reply in a thread that's two years old? Or is that your own site? :roll:

sreeram_kasyapa · May 1, 2006

instantaneous power is something which u get by d product i*i*z.. where i is the instantaneous sinusoidal current and z is d impedance of load.. where as rms power is something which u get by Irms*Irms*R or Vrms*Vrms/R ... generally u can easily get Vrms and R and find d average power. but calculating instantaneous power is quite complex and changes from case to case..

audioguru · May 1, 2006

Many amps and speakers are rated in "Peak" or Maximum" power, which is at the peak voltage and current of a sinewave. 1.414 times both the voltage and the current equals exactly double the true continuous power.

10% distortion is also common with an amp's power rating because when the amp is heavily clipping like that then its output power is approaching double the amount of power it has with a square-wave output.

Music power is measured very briefly before the power supply's voltage sags from having a load. Phoney baloney peak music power.

Philips and ST Micro have new power ratings methods for their amp ICs that seem to triple the true power.

Nigel Goodwin · May 2, 2006

audioguru said:
Many amps and speakers are rated in "Peak" or Maximum" power.

Only low quality ones, any decent quality amplifiers or speakers will give RMS ratings.

lord loh. · May 3, 2006

They call it PMPO - Peak Max Power Output...

Some speakers in the Indian market have a 22,000W PMPO...An article I had just read demistified this crap... The author pointed out that why do the manufacturers not supply a small pocket nuclear reactor to supply that knind of power.... ha ha ha...

Styx · May 3, 2006

lord loh. said:
They call it PMPO - Peak Max Power Output...

Some speakers in the Indian market have a 22,000W PMPO...An article I had just read demistified this crap... The author pointed out that why do the manufacturers not supply a small pocket nuclear reactor to supply that knind of power.... ha ha ha...

I hate such terminology, it is why I hate dealing with American Power electronic manufactures, ABB like doing similar things as well (on an IGBT front) good old Eupec and Semikron tell you exactly how much energy the IGBT can handle,

RMS wats to watts

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