Amp Gain / Amp power

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Amp Gain / Amp power

Postby ARE » Mon May 03, 2004 7:28 pm

What's the general relationship between amp gain and amp power? If gain is the ratio between input signal and output signal, how does power come into play?
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Postby SoFtCliPpEr » Mon May 03, 2004 8:06 pm

Amps are the "middlemen" in any system. They get low level signals from our source component and then cranks them up to levels essential to move speaker diaphragms in the process of producing sound.

They are designated to perform this gargantuan task which explains why so often their bulk and size will show. Power is the capability to do work. In the case of audio amps the more power you have the louder your speakers can play. By and large MORE is BETTER 100W is better than 50W while 150W is better than 100W and so on.

Ohms law dictates that for a given voltage in a circuit ,the lower the impedance ,the higher the current. Simply because POWER is voltage times current an audio amp can usually deliver more watts as the load impedance is reduced. Up to a certain point the amp can no longer juice up any more current without shutting down (sucked out) or throttling back to protect it's output transistors from overheating.

Distortion thus becomes a part of the amps specification. As the amp runs out of steam DISTORTION levels rises. And as the amp is completely overloaded it cuts off the peaks
of waveforms a condition generally described as "clipping" which relates to very severe distortion levels.

Check this out buddy http://webhome.idirect.com/~jadams/electronics/ohm.htm
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Re: Amp Gain / Amp power

Postby av_phile » Tue May 04, 2004 10:22 am

ARE wrote:What's the general relationship between amp gain and amp power? If gain is the ratio between input signal and output signal, how does power come into play?


You're right in saying that gain is a ratio. It does not have any unit. Mathematically, it is expressed as A(gain) = output/input. And the ratio applies to voltage, current as well as power. With power, amplifier gain is better measured logarithmically using decibels. A gain of 1 means no change and this is reference to 0db. If i recall right, a gain of 15 from an input of 1v to an output of 15v is about the same as a 12db power gain.
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Postby amandarae » Tue May 04, 2004 10:48 am

Just to add on the excellent response above. Here is how I understand the question.

Gain and power are related. Gain be either voltage, current, or in our case power. Their relationship is when the unit of measurement of dB (decibels) comes into play.

dB= 10 log Pinput/Poutput
= 20 log Vin/Vout
=10 log Iin/I out

All of the above is a measure of the relative strenght of a signal parameter.

In our consideration (audio amps), we can say that gain is the ratio of the output to the input signal and it is unitless. But if we express gain in terms of a reference point, say voltage, then it should be express in dB and is now called as simply a voltage gain. Similarly, power in unit of Watts, Volt-Ampere Reactive(VAR), or Volt-Ampere(VA) are just that, a measurement of power. To have it as Power Gain, then a reference point should be chosen (i.e. 1mW for dBm, 1V for dBv, dBm + 90 for dBrn, etc.)

In summary, a gain is a ratio of the input signal to the output signal express linearly (scalar). Whereas power is a unit of measure of an electrical signals (either watt, var, va) express vectorially, meaning it is directed to something. One cannot relate to another unless a reference point is use arbitrarily, thus the dB equations above.

hope this helps....
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Postby SoFtCliPpEr » Tue May 04, 2004 11:16 am

amandarae,

Thanks for the added data. Thus then is it correct to say that since the output signal being conveyed by the signal source is "fixed" the matter of the amplifier's gain is is dictatated by it's potentiometer which in turn is transmitted by the amps output into the speakers? Or would the impedance load determine the power the amp has to juice out or both?
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Postby amandarae » Tue May 04, 2004 2:25 pm

SoFtCliPper,


Thus then is it correct to say that since the output signal being conveyed by the signal source is "fixed" the matter of the amplifier's gain is is dictatated by it's potentiometer which in turn is transmitted by the amps output into the speakers?


Yes, I really think so. The important word here (and you nailed it) is "fixed" input.

The amplifier gain is specified with a fix amount of sensitivity. I am assuming that since you mentioned potentiometer, then it has to do with how the amps are biased. When the sensitivity requirements are satisfied, no matter how much the input signal is, the corresponding output is base on its magnitude. For example, for an amp that has a 20 dB of gain, the ratio of the output to the input wether the input signal is 500 mV or 1.5 volts should be 20 dB as long as both inputs satisfies the level where the sensitivity of the amp is reach and assuming that the amp has a linear response and we are operating on the active region of the active elements. Also, it is worthwhile to note that amps specs includes the minimum input to reach maximum rated power. This parameter is very handy in evaluating the voltage and power gain of the amp.

Or would the impedance load determine the power the amp has to juice out or both?


Yes again but this has no relation to the gain. You are right, power is the one affected by this. The impedance will directly affect the power (needed) delivered by the amp to reach a certain magnitude (ex. 90 dB SPL )or level because any change in the impedance affects the current needed to maintain that level.
But the gain of the amp is fix.



Geesh....I am getting ahead of myself here again. SoFtCliPper, that is all I know and hopefully it makes sense to you. :)
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Postby SoFtCliPpEr » Tue May 04, 2004 4:49 pm

amandarae,

AYE you cleared up a lot of cobwebs on my head with your inputs.

Thanks bud
:)
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Re: Amp Gain / Amp power

Postby johnmarc0 » Tue May 04, 2004 5:34 pm

ARE wrote:What's the general relationship between amp gain and amp power? If gain is the ratio between input signal and output signal, how does power come into play?



To set the reocrd straight, Gain is the ratio between input and output powers to a device. If a device is amplifying the gain is positive and if it loses power (i.e. passive pre) the gain is negative or simply a loss. Since gain is a linear dimension in the early 1900's they decide that gain is best expressed according to the human hearing characteristics and that is logarithmic. So converting a linear scale to logarithmic is just simply apply the logarithm of that quantity. In the case of power...

log G = Bel

but such powers of a Bel is extremely high so they decided that maybe 1/10 scale of a bel is much more appropriate.

the term "Log G x 1/10" is expressed also as "10 log G" or simply called deciBel.

Be careful this only applies to power remember in ohms law power can be expressed in terms of voltage and resistance as V^2*R so if we apply the decibel equation to two powers (pin and pout)

10 log (V1^2*R1)/(V2^2*R2)

and if we consider R1=R2 (a condition where the input impedance is the equal to the output impedance), we can re format the equation as


10 log (V1/V2)^2 x 1 (R1/R2 =1 since they are the same impedance or simply

10 log (V1/V2)^2 then applying rules of logarithm we can further simplify

2 x 10 log V1/V2 or simply

G(dB)=20 log V1/V2

So in this statement ....

av_phile wrote: ......... If i recall right, a gain of 15 from an input of 1v to an output of 15v is about the same as a 12db power gain.


is only true if they are using the same input and output impedance, else in the case of audio amplifiers where the input impedance is bet 600 ohms and 2,000 ohms and the output is 8 ohms, the application of decibel is misleading....

haba ba nung sinabi ko???
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Postby ARE » Tue May 04, 2004 6:17 pm

Whew, that is definetely a lot to ponder on. If you dont mind johnmarco, maybe we can discuss this when the second part of Tubes 101 pushes through... and I hope it happens soon, cant wait to tinker on a SET monoblock.

Anyways, on the topic again, gain would be an amplifier's inherent characteristics, while power would always be dependent on the associated equipment (or within a specific working limit). Is it safe to say that?

From a layman's perspective, gain (positive) correlates to 'amplify' which relates to volume increase. Now having said that, it gets confusing that an approximate 3 db increase results from doubling the power, specially say between two amps, (1) 100W and (1) 200W but both with the same gain.

I am most certainly sure that there something with my line of thinking :roll: .
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Postby johnmarc0 » Tue May 04, 2004 6:51 pm

ARE wrote:gain would be an amplifier's inherent characteristics,
while power would always be dependent on the associated equipment (or within a specific working limit). Is it safe to say that?


That is a qualified "yes", then there is sensitivity also expressed in dB where it shows the dynamic range of powers that the amplifier can be driven, for example some amp-pre combos can overdrive the amp at 3 o'clock while some combos do not overdrive the amp even at full rotation. This volume space between distortion pt and full throttle is sometimes called " headroom". (kung sa baril eh chamber headspace hehehehe)



ARE wrote:From a layman's perspective,
gain (positive) correlates to 'amplify' which relates to volume increase.


That is a yes yet again

ARE wrote:it gets confusing that an approximate 3 db increase results from doubling the power, specially say between two amps, (1) 100W and (1) 200W but both with the same gain.


lets do a short math exercise dBw is dB gain over 1 watt reference hence...

10 log 100W/1W = 20dBw

also for the 200W amp

10 log 200W/1W = 23dBw


200W=23dBw
100W=20dBw
difference=3dB

Now we can truly say that the 200W amp offers relative power equivalent to 3dB over the 100W amp.

They structured it this way as the human hearing usually do not perceive better than 3dB, meaning if the power does not double or halve we can not perceive spl volume changes, some may debate that they can hear 2dB changes (we should be smoking their dope) but they are from another planet to my opinion.

Surprisingly, all you need is three loudness steps (three 3dB steps) to make music musical, even an orchestra do not change 9dB in loudness, so to my opinion 20dBw is overkill to perceive comfortable listening. Most orchestral pieces do not deviate more than 9dB (or maybe rarely, try read the notes on the pieces if you can).
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Postby ARE » Tue May 04, 2004 7:29 pm

johnmarc0 wrote:
ARE wrote:it gets confusing that an approximate 3 db increase results from doubling the power, specially say between two amps, (1) 100W and (1) 200W but both with the same gain.


lets do a short math exercise dBw is dB gain over 1 watt reference hence...

10 log 100W/1W = 20dBw

also for the 200W amp

10 log 200W/1W = 23dBw


200W=23dBw
100W=20dBw
difference=3dB

Now we can truly say that the 200W amp offers relative power equivalent to 3dB over the 100W amp.




That was quite clear but with 'the same gain' I was referring to the inherent gain of the amp.

Say two Classe amplifiers:
CA-101 rated at 100 watts
CA-201 rated at 200 watts

From your example then they would have a gain of 20 and 23 dBw resepctively.
However, both have been specified by the manufacturer to have a gain of 29.02 db.
That was the gain I was referring to. What's the difference?
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Postby arnoldc » Wed May 05, 2004 7:20 am

ARE, are these integrated? if so, the manufacturer must be talking about the gain stage, not the power stage. or the gain of the driver stage, for a power amp.

i'm just making a guess though.
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Postby ARE » Wed May 05, 2004 5:24 pm

arnoldc, these are stereo amps, not integrated. Thanks for noting 'gain of the driver stage'. I'll do further reading on this. Thanks.
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Postby av_phile » Wed May 05, 2004 6:50 pm

ARE wrote:arnoldc, these are stereo amps, not integrated. Thanks for noting 'gain of the driver stage'. I'll do further reading on this. Thanks.


You mean stereo POWER amps?
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Postby ARE » Wed May 05, 2004 8:48 pm

Yup, stereo power amps
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Postby av_phile » Sat May 08, 2004 1:32 pm

There is another aspect of stereo amplifier power or perceived loudness that had me baffled in the past. On some receivers and integrateds, it seems the volume control at the 10 o'clock position yield so much more loudness than the same volume position in a preamp + power amp combination of the same power, both conservatively rated and using the same player and source. I have some idea behind this, but would be interested about your thoughts.
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Postby joe3rp » Sat May 08, 2004 7:52 pm

av_phile wrote:There is another aspect of stereo amplifier power or perceived loudness that had me baffled in the past. On some receivers and integrateds, it seems the volume control at the 10 o'clock position yield so much more loudness than the same volume position in a preamp + power amp combination of the same power, both conservatively rated and using the same player and source. I have some idea behind this, but would be interested about your thoughts.


I don't know why a lot of you guys are so fixated on the volume control position...wow at 10 o'clock mas malakas ang tunog!!!!!

1- the common volume control (potentiometer) - when not in maximum volume postion results in a lot of the signal going through the resistor/wiper.

2- as long s you get the acceptable volume to come out of the speaker! - If you have the capability to adjust the volume to get the speaker to clip and distort and sound awful - why do you need that capability! If you max out at 10 o'clock - what will you need the other 11 - 12 - 1 -2 - 3 - 4- 5 - 6 - decoration!
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Postby mickey » Mon May 10, 2004 4:11 pm

Another parameter worth taking a look at in amps is the input sensitivity, which is the input signal level that will drive the amp to clipping or in another way of putting this max out your amp. the lower the value of this then the higher the gain of your amp. intergrated amps have very low input sensitivity (below 0.3 V ) so they can be connected directly to CD players with output voltages of .5V up
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Postby RU9 » Tue May 11, 2004 9:50 am

mickey wrote:Another parameter worth taking a look at in amps is the input sensitivity, which is the input signal level that will drive the amp to clipping or in another way of putting this max out your amp. the lower the value of this then the higher the gain of your amp. intergrated amps have very low input sensitivity (below 0.3 V ) so they can be connected directly to CD players with output voltages of .5V up


Hi Mickey,

I have these two set-up, care to explain the difference in loudness?

Set-up 1
CD Player-->TONO Preamp(vol 12:00)-->40 watt INTEGRATED amp (vol 12:00)
Sound is LOUD but listenable.

Set-up 2
CD Player-->TONO Preamp(vol 9:30)-->70 watt POWER amp
Sound is VERY LOUD (ear-piercing), is this normal for the TONO preamp?

Thanks.

Louie
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Postby joe3rp » Tue May 11, 2004 9:54 am

RU9 wrote:
mickey wrote:Another parameter worth taking a look at in amps is the input sensitivity, which is the input signal level that will drive the amp to clipping or in another way of putting this max out your amp. the lower the value of this then the higher the gain of your amp. intergrated amps have very low input sensitivity (below 0.3 V ) so they can be connected directly to CD players with output voltages of .5V up


Hi Mickey,

I have these two set-up, care to explain the difference in loudness?

Set-up 1
CD Player-->TONO Preamp(vol 12:00)-->40 watt INTEGRATED amp (vol 12:00)
Sound is LOUD but listenable.

Set-up 2
CD Player-->TONO Preamp(vol 9:30)-->70 watt POWER amp
Sound is VERY LOUD (ear-piercing), is this normal for the TONO preamp?

Thanks.

Louie


Which sounds better when you adjust set-up 2 volume to to a listenable volume?
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