Relationship between input voltage and output power?

[Endymion Joshi-Godrez]

Not a particularly intelligent question, but if an amp has a maximum input voltage of 4V, but you feed to 2V, whats the relationship between that change and the maximum output power of the amp?

 

[Blumlein 88]

Not a particularly intelligent question, but if an amp has a maximum input voltage of 4V, but you feed to 2V, whats the relationship between that change and the maximum output power of the amp?

1/4 th the power at half voltage.

Power in watts equal voltage time amps.

Amps equal voltage divided by resistance.

So for a given resistance half voltage means half amps leading to 1/4 th the watts.

 

[Everett T]

Not a particularly intelligent question, but if an amp has a maximum input voltage of 4V, but you feed to 2V, whats the relationship between that change and the maximum output power of the amp?

More information is needed. The maximum numbers may be relevant or not in each case. You need to know at what input level to drive the amp to full power. Some power amps have adjustable input gain to match your preamp's output, some don't, the latter is when you really need to pay attention.

@peng can give you the formula in EE terms but you would need to give specific examples.

 

[Blumlein 88]

More information is needed. The maximum numbers may be relevant or not in each case. You need to know at what input level to drive the amp to full power. Some power amps have adjustable input gain to match your preamp's output, some don't, the latter is when you really need to pay attention.

@peng can give you the formula in EE terms but you would need to give specific examples.

Well he already said 4 volts max presumably for max power.

 

[Everett T]

Well he already said 4 volts max presumably for max power.

Yeah, I didn't want to assume, just needed more specifics.

 

[peng]

More information is needed. The maximum numbers may be relevant or not in each case. You need to know at what input level to drive the amp to full power. Some power amps have adjustable input gain to match your preamp's output, some don't, the latter is when you really need to pay attention.

It may not be relevant in his case, but he is simply asking about the relationship between the change in input voltage to the amp (presumably he meant the power amp) and the maximum power output of the amp so we can give him a simple answer in a generic way.

@peng can give you the formula in EE terms but you would need to give specific examples.

Assuming the OP did not make any typo, then as @Blumlein 88 cited, according to the OP, "an amp has a maximum input voltage of 4V".
So the simple formula for calculating power is the power formula such as those given on the best (that I know of) website for electrical formula related to amps:

Voltage current resistance and electric power general basic electrical formulas mathematical calculations calculator formula for power calculating energy work equation power law watts understandimg general electrical pie chart electricity calculation

Electric power calculator calculation general basic electrical formulas mathematical voltage electrical equation formula for power calculating energy work power watts calculator equation power law current charge resistance converter ohm's law and power law power formulae formulas understandimg...

sengpielaudio.com

Power P = V × I = R × I² = V² / R in watts W

That's obviously for resistor loads only, so phase angle effects are ignore but for the OP's question that won't make a difference because he can easily see that power output varies with the square of the voltage:

Being a square/square root relationship, half the voltage would result in one quarter power.

 

[audio_tony]

Surely this is not about wattage, but about gain?

The output voltage for 2v will depend on the gain (either expressed on dB or a multiplication factor).

Therefore if 4v = maximum output, 2v = half maximum output.

 

[Blumlein 88]

Surely this is not about wattage, but about gain?

The output voltage for 2v will depend on the gain (either expressed on dB or a multiplication factor).

Therefore if 4v = maximum output, 2v = half maximum output.

Look at the formula in peng's post. Half input voltage will result in half output voltage whatever the gain. Gain is the same. Output power is a quarter.

 

[peng]

Surely this is not about wattage, but about gain?

He said "power" though. If it is about output voltage and/or gain, Everett T's comments would apply, that is, we would need to know about the gain.

The output voltage for 2v will depend on the gain (either expressed on dB or a multiplication factor).

Therefore if 4v = maximum output, 2v = half maximum output.

That's not correct, I guess you made a typo?

 

[Endymion Joshi-Godrez]

Sorry for the confusion. Yes I was making the presumption that the maximum input voltage of the amp is the only way to achieve the maximum output power of the amplifier. To be frank, I just needed a very large ballpark answer. Knowing that it can be 1/4 is more than substantial enough to inform me of my next purchase.

To be accurate, this was in regards to me using a qudelix with a heavy preamp attenuation into a portable amplifier. The qudelix will tell you the voltage output, which for me was 0.65V out of the 2V unbalanced output, and 1.43V out of the 4V balanced output. Most portable amps recommend 2V input regardless of unbalanced or balanced outputs. Some go all the way to 4V for balanced output.

Of course, the problem is it does not tell you if the maximum rated output power is only achieved at the maximum input voltage. Is there a reason why input voltage needed to achieve the maximum output power would be lower than the maximum recommended input voltage of the amplifier?

 

[staticV3]

Sorry for the confusion. Yes I was making the presumption that the maximum input voltage of the amp is the only way to achieve the maximum output power of the amplifier. To be frank, I just needed a very large ballpark answer. Knowing that it can be 1/4 is more than substantial enough to inform me of my next purchase.

To be accurate, this was in regards to me using a qudelix with a heavy preamp attenuation into a portable amplifier. The qudelix will tell you the voltage output, which for me was 0.65V out of the 2V unbalanced output, and 1.43V out of the 4V balanced output. Most portable amps recommend 2V input regardless of unbalanced or balanced outputs. Some go all the way to 4V for balanced output.

Of course, the problem is it does not tell you if the maximum rated output power is only achieved at the maximum input voltage. Is there a reason why input voltage needed to achieve the maximum output power would be lower than the maximum recommended input voltage of the amplifier?

More relevant than output power is output volume IMO.

Halve the input voltage and output power will drop by 75%, but the actual loudness will only drop by 35%.

 

[GXAlan]

To be frank, I just needed a very large ballpark answer

This is an issue of gain.

dB Gain Calculator

Determine dB gain by entering initial and final power levels into the dB gain calculator.

www.omnicalculator.com

Some low gain amps need a lot of input voltage to hit a target output power (and therefore speaker volume) while other high gain amps are the opposite.

In theory, high gain preamps and low gain amps give you the best measured SNR. That’s because we typically listen at lower watts that we think and “residual noise” is fixed and low output voltage means that the noise is a higher percentage.

We see gear like Arcam AV products measuring poorly but people liking it in real practice. This is because Arcam amps have 31 dB gain. You if you were listening at 2.83V, the preamp would just be putting out 80 millivolts! You never really get to the “target 4V balanced out” that the SINAD chart focuses on.

The Benchmark AHB2 can drop its gain to as low as 9 dB, and so 1V preout is what leads to 2.83V at the speakers. You can see the slope of most gear showing increasing SINAD with increasing output voltage…

The problem is of course, when your preout is at max output voltage and your gain is still too low…

 

[peng]

Sorry for the confusion. Yes I was making the presumption that the maximum input voltage of the amp is the only way to achieve the maximum output power of the amplifier. To be frank, I just needed a very large ballpark answer. Knowing that it can be 1/4 is more than substantial enough to inform me of my next purchase.

To be accurate, this was in regards to me using a qudelix with a heavy preamp attenuation into a portable amplifier. The qudelix will tell you the voltage output, which for me was 0.65V out of the 2V unbalanced output, and 1.43V out of the 4V balanced output. Most portable amps recommend 2V input regardless of unbalanced or balanced outputs. Some go all the way to 4V for balanced output.

Of course, the problem is it does not tell you if the maximum rated output power is only achieved at the maximum input voltage. Is there a reason why input voltage needed to achieve the maximum output power would be lower than the maximum recommended input voltage of the amplifier?

Can you provide the full specifications of your power amp?

I don't recall seeing power amp specs that include the "maximum" input voltage.

 

[Endymion Joshi-Godrez]

Can you provide the full specifications of your power amp?

I don't recall seeing power amp specs that include the "maximum" input voltage.

Some examples would be the centrance ampersand, which states a "nominal input voltage" of 2V:

Ampersand - Centrance

AMPERSAND Headphone Power Amplifier Portable Amplifier with balanced XLR and Pentaconn outputs delivers up to 6W of audio power. Hear your planar headphones come alive with Ampersand’s clean, confident, and quiet power. SHOP NOW CEntrance / HEDD combo had punch, ample low-end, clarity, and...

centrance.com

The astell and Kurn P10, which states a "maximum imput voltage" of 4V:

Astell&Kern

The ibasso PB5 states a "maximum line input" of 2.5V:

One moment, please...

Apparently the input voltage for the highest possible output of the Topping NX7 is just 1.4V, but there is no confirmation of this.

I'm not reping any of these. They're just examples.

 

[Endymion Joshi-Godrez]

I think I might be confusing maximum input voltage and input sensitivity. Can someone please explain what topping is using to calculate input sensitivity?

Is this the amount of input voltage needed to achieve the same volume? If it is, does this also mean that lowing the gain allows you to increase the voltage input before distortion? Can the Topping nx7 allow for upto 13V input?

 

[DonH56]

Power amplifiers have input sensitivity, max input, gain, rated output, max output, etc. Input sensitivity is the input voltage needed to achieve rated output voltage (and thus power for specified load and distortion). Max input could be where input or output clipping occurs, i.e. the voltage excursion limits of the input (or output) stage. Amplifiers can usually provide greater output for brief periods than their rated specifications, e.g. headroom. And note that rated output is for a given power into a given load at a specified distortion level. The same amp could be rated for different power output (and thus different input voltage) by changing the distortion spec from say 0.01% to 1%.

 

[Endymion Joshi-Godrez]

Power amplifiers have input sensitivity, max input, gain, rated output, max output, etc. Input sensitivity is the input voltage needed to achieve rated output voltage (and thus power for specified load and distortion). Max input could be where input or output clipping occurs, i.e. the voltage excursion limits of the input (or output) stage. Amplifiers can usually provide greater output for brief periods than their rated specifications, e.g. headroom. And note that rated output is for a given power into a given load at a specified distortion level. The same amp could be rated for different power output (and thus different input voltage) by changing the distortion spec from say 0.01% to 1%.

So is the input sensitivity just a theoretical condition needed to achieve the maximum output voltage. Or is topping, on top of that, also implying that you can feed 13V at low gain with the same THD as 1.5V at high gain?

 

[audio_tony]

Look at the formula in peng's post. Half input voltage will result in half output voltage whatever the gain. Gain is the same. Output power is a quarter.

Yes, I made the mistake of thinking in terms of voltage gain, not power gain (completely glossing over the fact that the OP mentioned "power output").

 

[staticV3]

Can someone please explain what topping is using to calculate input sensitivity?

Topping's input sensitivity = voltage required at the input to clip the output with volume turned up all the way.

You can input higher voltages by just not having the volume turned up all the way.

 

[peng]

So is the input sensitivity just a theoretical condition needed to achieve the maximum output voltage.

Sort of, but not quite, as DonH56 said:

Max input could be where input or output clipping occurs, i.e. the voltage excursion limits of the input (or output) stage.
So "maximum output voltage" also need the test condition to be specified, such as "at 0.05% THD+N", otherwise, like Don said, "where ... clipping occurs.." would be a reasonable assumed condition.

Or is topping, on top of that, also implying that you can feed 13V at low gain with the same THD as 1.5V at high gain?

Topping did not say that explicitly, but for "ball park" purposes, yes, that would be a reasonable assumption.

So, I think DonH56 answered your questions already, if not, feel free to ask again.