Relationship between input voltage and output power?

[Audiofire]

What is the right interpretation of input sensitivity for an amp?

This came out of a discussion in another thread between @peng and I and a subsequent PM exchange. We agreed that this was a confusing issue. Assume just unbalanced inputs for the following since the unbalanced vs balanced spec is unrelated to this fundamental question. Bringing that in will...

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[Endymion Joshi-Godrez]

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.

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.

I realise that now. The THD must be the same or the input sensitivity measuments would be weighted for a given gain . So maximum output voltage could just mean that this is the hottest input the amp will allow, NOT the input that is required to give you the maximum output voltage at the highest gain. If there is enough gain, the voltage I would need to achieve the same volume could be considerably lower. Its a shame only topping show the input sensitivity of all gain settings.

 

[staticV3]

I realise that now. The THD must be the same or the input sensitivity measuments would be weighted for a given gain . So maximum output voltage could just mean that this is the hottest input the amp will allow, NOT the input that is required to give you the maximum output voltage at the highest gain. If there is enough gain, the voltage I would need to achieve the same volume could be considerably lower. Its a shame only topping show the input sensitivity of all gain settings.

Topping's way of specifying input sensitivity is somewhat useless, as you can just calculate it from maximum output power and gain.

More interesting IMO is the maximum input voltage, so the highest voltage before the input clips. Unfortunately barely any manufacturer specifies it, and barely any reviewer measures it.

 

[Joesax]

Interesting I was asking the same question in another thread. In my case

The Benchmark AHB2 amp has variable gain. At a gain of 17db the input sensitivity is 4v to drive rated power.

I like to run my DAC directly into the amp with the DAC set to its low output impedance of 150 Ohms. This nets an output voltage of 1.75v.

It sounds fine and is the best combination I’ve tried but I was curious to know exactly how much power? Watts? I’m sacrificing with this combination of sensitivity/output voltage.

So I can only drive the amp to 25% of its rated power?

 

[Elitzur–Vaidman]

So I can only drive the amp to 25% of its rated power?

Slightly less than 25%, but yes. I wouldn't worry about it unless you find yourself needing more volume. And even then a 4V input would only net you an additional ~7db of headroom

 

[Joesax]

Ok then a non issue

 

[staticV3]

Interesting I was asking the same question in another thread. In my case

The Benchmark AHB2 amp has variable gain. At a gain of 17db the input sensitivity is 4v to drive rated power.

I like to run my DAC directly into the amp with the DAC set to its low output impedance of 150 Ohms. This nets an output voltage of 1.75v.

It sounds fine and is the best combination I’ve tried but I was curious to know exactly how much power? Watts? I’m sacrificing with this combination of sensitivity/output voltage.

So I can only drive the amp to 25% of its rated power?

With the AHB2 set to High gain, 1.75V input is enough for 100W at 4Ω or 50W at 8Ω.

At Medium gain, you'll get 55W at 4Ω and 27W at 8Ω.

 

[Joesax]

I guess I can go back to the High Impedance setting on the DAC which will give me 3.57v output into the 4v amp sensitivity. I’ll be upgrading to a different amp next month that has a several gain settings: 28db, 25db, 22db and 16db. The highest gain setting has a sensitivity of 1.37v. I’ll have to try them all. So many combinations.

 

[staticV3]

I guess I can go back to the High Impedance setting on the DAC which will give me 3.57v output into the 4v amp sensitivity. I’ll be upgrading to a different amp next month that has a several gain settings: 28db, 25db, 22db and 16db. The highest gain setting has a sensitivity of 1.37v. I’ll have to try them all. So many combinations.

Usually, the highest DAC output and lowest Amp gain will give you the cleanest signal.

 

[Joesax]

Related question. If I’m driving the amp to 27w at 8 ohms I assume what happens when there is a large dynamic peak in music the amp has access to the power it needs to reproduce that peak? If so then 27w is plenty for normal listening as long as the amp has power in reserve to handle dynamic peaks while being driven to 27w.

 

[staticV3]

Related question. If I’m driving the amp to 27w at 8 ohms I assume what happens when there is a large dynamic peak in music the amp has access to the power it needs to reproduce that peak? If so then 27w is plenty for normal listening as long as the amp has power in reserve to handle dynamic peaks while being driven to 27w.

If Medium gain at 1.75V input is loud enough for you, then that means that all dynamic peaks in your music are currently below 27W in amplitude.

 

[Joesax]

Ok. Here’s another way I’m understanding it

I’m listening to the amp at mid gain (17db) and driving it with the DAC’s 1.75 v. I’m listening to a piano recording at the volume resulting from the full output voltage and the resulting 27w. My volume control is full up. Then a full dynamic orchestra crescendo happens. I would think that the amp can deliver move watts to handle that dynamic aspect of the recording since it does have 100w before clipping. But can the DAC handle it? Or does it clip?

 

[IAtaman]

Ok. Here’s another way I’m understanding it

I’m listening to the amp at mid gain (17db) and driving it with the DAC’s 1.75 v. I’m listening to a piano recording at the volume resulting from the full output voltage and the resulting 27w. My volume control is full up. Then a full dynamic orchestra crescendo happens. I would think that the amp can deliver move watts to handle that dynamic aspect of the recording since it does have 100w before clipping. But can the DAC handle it? Or does it clip?

No. You are confusing the max with average, that is what staticV3 was trying to explain. If 1.75V is the input required for your amp to be able to deliver the peak dynamic range of the crescendo, the output of your DAC at relatively quiet piano sections would be much less than 1.75V.

 

[Joesax]

Ok thanks. Got it.