Watts vs Current

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dflee

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Watts vs Current
« on: 9 Jul 2019, 01:55 pm »
I'm a complete novice when it comes to anything electric so am asking.
What makes a low wattage amp high current? And is a high wattage amp
high current in order to be high wattage or can you have a high wattage amp
with low current?
Just trying to figure something out. I've been told that a high current amp is good.

Don
ps: If this has been discussed before, please point me in that direction

Freo-1

Re: Watts vs Current
« Reply #1 on: 9 Jul 2019, 02:15 pm »
The short answer is: Watts are defined as follows:  (A watt is the same regardless of the amp that supplies it)


In the formula Power = I x V, the power is given in watts, I is current in amperes and V is volts. The second formula that may be utilized to calculate watts to voltage is Power = V squared / R, where R is the resistance in ohms. In one method, write the power formula as Power in watts = I x V.

So, for audio, when one refers to a "high current" amp, it simply means that there is a current reserve for speakers that have low impedance.  Any high wattage amp should be capable of generating sufficient current to drive the speakers.  High powered SS amps that double the wattage from 8 ohms nominal to 4 ohms nominal would be considered a voltage source, since it supplies the same voltage regardless of the current draw.  A tube amp is considered a current source, as the taps will provide the same current level regardless of the voltage tap.
Does that help?
« Last Edit: 9 Jul 2019, 08:14 pm by Freo-1 »

I.Greyhound Fan

Re: Watts vs Current
« Reply #2 on: 9 Jul 2019, 07:27 pm »
Here is a good discussion on this topic that will help-

https://forum.audiogon.com/discussions/watts-versus-current

A rough analogy is to think of watts as horse power and current as torque.  Both are needed for high speed.  A high HP low torque engine will go 150mp but a high HP engine with high torque will get you there sooner.

Or think of a pipe,  amps are the volume of water flowing through a pipe and voltage would be the water pressure.

amps x voltage= watts
« Last Edit: 9 Jul 2019, 09:04 pm by I.Greyhound Fan »

randytsuch

Re: Watts vs Current
« Reply #3 on: 9 Jul 2019, 07:36 pm »
Another way to think of it is
Power = I squared x resistance
Where I is current.
Resistance would be nominal resistance of your speaker, usually 8 or 4.

Since resistance is constant, higher current is higher power.

But this is simplified, in real life a speaker is not a constant 8 ohm load.
You need to look at the impedance of the speaker.  Impedance can be thought of as resistance over frequency.
As you go from 20 hz to 20 khz, the impedance curve can change a lot.  Depends on the drivers and the crossover design.
So 8 ohms would be the nominal value from 20 to 20k, but the actual value at any given frequency can vary.

As to if "high current" will sound better?
Can't answer that. 

Randy


FullRangeMan

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Re: Watts vs Current
« Reply #4 on: 9 Jul 2019, 07:43 pm »
Don, I like the simple formula :
Voltage(tension) x Amperage(current) =Watts  or

V x A =W

I.Greyhound Fan

Re: Watts vs Current
« Reply #5 on: 9 Jul 2019, 08:23 pm »
Don, you can have a high watt amp with lower current.  Just look at the cheap high wpc AVR's.  Many claim 125 to 150 wpc and are class AB.  They weigh close to nothing and most are not high current.  Compare that to say for example, a Parasound A23 amp that weighs in at 34 pounds and produces 45 peak amps at 150 wpc.

As for a high current amp sounding better, there are a lot of other factors to consider such as speaker impedance, efficiency etc.  I can tell you this, my Magnepans sound fuller and better with higher current.

Elizabeth

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Re: Watts vs Current
« Reply #6 on: 9 Jul 2019, 08:55 pm »
My favorite simple picture explanation is voltage is the water pressure in a pipe. The diameter of the pipe is the amperage.
Watts is how much water per unit you get out of your pipes.
SO a narrow pipe, with really high pressure can give you the same amount of water over time, as a larger pipe with much lower water pressure.
Fire hose vs tidal wave....
added thinking it over. the fire hose vs a tide.. (tidal wave has a different connotation...)
« Last Edit: 10 Jul 2019, 03:03 pm by Elizabeth »

srb

Re: Watts vs Current
« Reply #7 on: 9 Jul 2019, 09:03 pm »
Don, you can have a high watt amp with lower current.  Just look at the cheap high wpc AVR's.  Many claim 125 to 150 wpc and are class AB.  They weigh close to nothing and most are not high current.

And that's why most of these less-expensive AVRs often specify on the rear panel to connect only 8Ω or 6Ω speakers, and some even have a rear panel impedance switch to limit current if you do connect 6Ω or 4Ω speakers (or possibly even 8Ω speakers that dip down to lower impedances).

Freo-1

Re: Watts vs Current
« Reply #8 on: 10 Jul 2019, 11:49 am »
And that's why most of these less-expensive AVRs often specify on the rear panel to connect only 8Ω or 6Ω speakers, and some even have a rear panel impedance switch to limit current if you do connect 6Ω or 4Ω speakers (or possibly even 8Ω speakers that dip down to lower impedances).



The switch on the AVR's actually drop the rail voltage so the units don't overheat due to the extra current draw that results from the lower impedance.  After all, a given wattage level is the same regardless of the source.

fredgarvin

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Re: Watts vs Current
« Reply #9 on: 10 Jul 2019, 04:08 pm »
I'm not believing anything until Dr. Mark chimes in.

Freo-1

Re: Watts vs Current
« Reply #10 on: 11 Jul 2019, 07:40 pm »

Don, does this answer your questions? 


While a watt is a watt regardless of the amp design, the amp can run out of steam if it's connected to a punishing load like a Kappa 9 or some ESL's. 

dflee

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Re: Watts vs Current
« Reply #11 on: 11 Jul 2019, 08:27 pm »
Thanks for asking Mr. Freo-1.
Am I correct in stating that having High current (related as watts in some cases) does help with peak energy?
If so then why don't manufacturers post the peak. I think they used to didn't they. I thought having a big peak
power meant reserve power and was a good thing yet Iv'e heard amps with a lot of wattage not be able
to handle certain music without getting muddied.

Freo-1

Re: Watts vs Current
« Reply #12 on: 11 Jul 2019, 10:02 pm »
Thanks for asking Mr. Freo-1.
Am I correct in stating that having High current (related as watts in some cases) does help with peak energy?
If so then why don't manufacturers post the peak. I think they used to didn't they. I thought having a big peak
power meant reserve power and was a good thing yet Iv'e heard amps with a lot of wattage not be able
to handle certain music without getting muddied.



No worries, happy to help.


The short answer is: not necessarily.  Peak energy (wattage) is a function of the load seen on the amp when the peak occurs.  So, if the speaker is providing a low impedance at the peak level, then, high current does help.  Remember, a SS amp like a Pass Labs that doubles current as impedance lowers allows the peaks to be better handled.


However, if the peaks are of higher impedance by the speakers, then more volts are required to support the required power.  McIntosh, with the autoformer, acts as a current source, in that it supplies the same current at the various impedance taps (the same approach used by tube amps).   


So, a 150 watt amp by Pass Labs at 8 ohms can output 300 watts at 4 ohms.  A McIntosh 300 watt amp with autoformer will output 300 watts at both 8 ohms and 4 ohms.  In this case, the McIntosh would be better able to handle peaks. 


The best method to sort out what amp works for your speaker is to get a impedance curve for your specific speaker.

dflee

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Re: Watts vs Current
« Reply #13 on: 12 Jul 2019, 12:15 am »
Thanks buddy. That puts it into perspective. Best explanation I've had.