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

March Audio

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I trust you on this:), but there is one example I can give, the ATI amps, that I thought may require closer scrutiny. Below are some specs for their two very similar products, the AT4000 seems to be a newer generation model that replaced the AT2000.

AT4000:
Rated 200 W, 8 ohms, 300 W 4 ohms, input sensitivity: 1.6 V, Gain: 28 dB, same for both unbalanced and balanced

AT2000:
Rated 200 W, 8 ohms, 300 W, 4 ohms, input sensitivity: 1.6 V, same for both unbalanced and balanced, Gain: 32 dB unbalanced (RCA), 28 dB balanced (XLR).

How would you reconcile the two, both have the same 1.6 V input sensitivity specs for both RAC and XLR inputs, but the AT2000's gain is 6 dB higher for the RCA inputs, yet the input sensitivity are the same 1.6 V for both RCA and XLR. If you do the math, 34 dB gain, 1.6 V input will result in an output of 800 W! So shouldn't the input sensitivity for the AT2000 be 0.8 V?

Now if you look at the AT4000, input sensitivity are again 1.6 V, same for both RCA and XLR, but now the gain is 28 dB for both inputs. So in this case, it would seem that the AT4000 would work better with an AV processor/preamp that has its XLR output 2X that of their RCA output, if the AVP measured much better in SINAD at 2 to 2.4 V than at 4 V output, such as the AV7705?

ATI's explanation for the difference in input sensitivity and gain between the AT2000 and 4000 (see below), seems fine, as they claimed they were able to "normalize the input voltage" for the AT4000 (the newer gen.) but I still have a little trouble with the specified input sensitivity, can't help wonder if there is a typo or two somewhere.

As someone from a reputable audio equipment manufacturer, I hope you can take a good look and shed some light on this. I have no trouble understanding the input sensitivity specs of Marantz, Yamaha, McIntosh, Parasound, and many other power amp's, just the ATI's for now, I found confusing.

When asked, apparently ATI's explanation for the difference specs between the 2000 and 4000 are as follow:

https://forums.audioholics.com/foru...-to-be-a-denon-avr.119013/page-6#post-1417210

The AT2000/3000 circuitry didn't allow us to normalize input voltage. The AT4000/6000 design allowed us to make input voltage the same for RCA and XLR, so that the same gain can be applied to both.

XLR output on most (not all) pre-amps is 6dB louder than the RCA output. But that's just a result of having two signal wires instead of one. That doubles the signal (and noise), so it's not like XLR has a better signal than the RCA, just twice as much of the same signal.

We haven't decided on output voltage for the ATP-16 or whether XLR and RCA will be the same.

To me, I would much prefer March Audio's specs for the P252, no input sensitivity specs, just gain, and that's good enough for me.
https://www.marchaudio.net.au/product-page/p252-stereo-250-watt-power-amplifier

Power Output
  • 2 Ohms - 180 W rms
  • 4 Ohms - 250 W rms
  • 8 Ohms - 150 W rms
Voltage Gain 26dB

That's because I can then calculate the input sensitivities easily, based on the rated output into 2,4, and 8 Ohms.

That would be:
  • 2 Ohms - 180 W rms (*Input sensitivity: 0.76 V)
  • 4 Ohms - 250 W rms (*Input sensitivity: 1.26 V)
  • 8 Ohms - 150 W rms (*Input sensitivity: 1.38 V)
* The input sensitivity figures are from my calculations only, not part of March Audio's specs. I could be wrong if by chance I made some silly mistakes.

With ATI's, I can do the same kind of calculations, but the way they specified, I can't help but wonder if I interpreted their specs correctly.

Have a read of the linked document in my previous post. It's a misconception that XLR signals need to be symmetric around an arbitrary ground reference and therefore double single ended voltage. It just happens that a common way of acheiving this is with the circuit above which does this.

ATI could have seperate input buffers for the xlr and RCA inputs. They could choose whatever gain they liked for them. However you can't therefore have the same input voltage sensitivity for both. It's an error.

Personally I wouldnt pay too much attention to the whole "sensitivity" thing. As you can see from your calculations above amplifier power ratings are not consistent WRT impedance of the load and a specific distortion limit. At the low end amps will be current limited and at the high end voltage limited. Speakers can and do vary from 2 ohms to maybe 20 ohms across the frequency range.

So where do you calculate it? What is applicable for the load your speakers present? Makes more sense to use gain as the spec and work from there. You will find that the vast majority of power amps are close to 26dB.

BTW the P252 sensitivity at 4 ohms is 1.58 volts rms.
 
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restorer-john

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Personally I wouldnt pay too much attention to the whole "sensitivity" thing.

I agree with this. As long as your source has sufficient voltage swing to be able to drive your amplifier to rated power and offer a reasonable range on the volume control to allow for low and high level recordings, you are good to go.
 

peng

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Have a read of the linked document in my previous post. It's a misconception that XLR signals need to be symmetric around an arbitrary ground reference and therefore double single ended voltage. It just happens that a common way of acheiving this is with the circuit above which does this.

ATI could have seperate input buffers for the xlr and RCA inputs. They could choose whatever gain they liked for them. However you can't therefore have the same input voltage sensitivity for both. It's an error.

Personally I wouldnt pay too much attention to the whole "sensitivity" thing. As you can see from your calculations above amplifier power ratings are not consistent WRT impedance of the load and a specific distortion limit. At the low end amps will be current limited and at the high end voltage limited. Speakers can and do vary from 2 ohms to maybe 20 ohms across the frequency range.

So where do you calculate it? What is applicable for the load your speakers present? Makes more sense to use gain as the spec and work from there. You will find that the vast majority of power amps are close to 26dB.

Thank you, that's what I thought, that they had an error in those specs. Could have been just a typo too I suppose. I may PM that AH member (he's a dealer) to email ATI about fixing it in their future publications.

BTW the P252 sensitivity at 4 ohms is 1.58 volts rms.

Thank you for letting me know, I edited them (all 3 were incorrect) so it won't mislead/confuse anyone, just in case. Don't know what happened as I used my Excel, and it does show 1.58 V for 4 ohms and 26 dB.
 
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peng

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A voltage gain of 26dB is ~20 (19.95) times.

150W RMS@8R is 34.64V RMS.
Divided by 20 is 1.73V

250W RMS@4R is 31.62V RMS
Divided by 20 is 1.58V

The amplifier is fairly linear until 2R where it hits the wall really hard, most likely in the form of current limiting and/or the PSU rails collapsing.

As we are seeing with the testing of the Class Ds, they are pretty much on the money for rated power outputs, so the specification numbers regarding gain are OK to base calculations on.

In the past, amplifiers were much more conservatively rated, often by around 20% as they rated for the full bandwidth (20-20K) at full rated power with very low THD figures from 250mW to rated power. A 150W/ch rated amplifier in the 1980s and 90s was typically 180W@8R, nearly double its official 8R rating into 4R, and often reached huge numbers for 2R. So although the "X volts for rated power output" specifications were usually valid, you had a lot more in reserve should you input more.

Thank you, no idea what I did, my spreadsheet was correct when I entered the data for 2,4,8 Ohms, I might have typed in the wrong "W" for each scenario. I actually had all 3 wrong:D, the 2 Ohm, 180 W should have been 0.95 V. Post edited now.
 
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aarons915

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You don't have to know the voltage at each volume setting just make sure:
Maximum clean output voltage from preamp >= Amplifier input sensitivity and you are set.

Answers are welcome from anyone but quoting you since it's close to my issue. I just bought some Neumann KH 120 and will be using a Denon's Pre outs to supply the signal to them. Can anyone elaborate on this answer? I know most Denon have been measured to supply around 1.5V of clean signal so if we want to stay under that is there a good rule of thumb?

My thoughts at the moment are to just play around with the knobs (input sensitivity and max output) until it feels about right relative to the volume dial on the Denon. I assume you just want to set the values to where they don't get too loud at too low a volume on the Denon and of course also get loud enough when the volume is turned higher.
 

Zek

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Play with the knobs so that the volume knob on the Denon is in the higher position due to the imbalance of the potentiometer in the lower position.
 

waynel

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Answers are welcome from anyone but quoting you since it's close to my issue. I just bought some Neumann KH 120 and will be using a Denon's Pre outs to supply the signal to them. Can anyone elaborate on this answer? I know most Denon have been measured to supply around 1.5V of clean signal so if we want to stay under that is there a good rule of thumb?

My thoughts at the moment are to just play around with the knobs (input sensitivity and max output) until it feels about right relative to the volume dial on the Denon. I assume you just want to set the values to where they don't get too loud at too low a volume on the Denon and of course also get loud enough when the volume is turned higher.
The KH 120 has adjustable sensitivity, I would start with the lower levels to avoid hiss.
 

aarons915

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The KH 120 has adjustable sensitivity, I would start with the lower levels to avoid hiss.

Thank you, that's how I started. I turned up the input sensitivity a bit from minimum but it works pretty well with the Denon and no clipping lights so it should be ok now.
 

nstzya

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You are worrying about things that don't need to be worried about. When was the last time you came across an amp that was totally incompatible with a pre due to widely disperate outputs, and sensitivities?

As the Hypex Ncore modules become popular, it actually does become an issue. In my case, I am wanting to go source direct to power amp. As my (and most) sources are limited to 2Vrms output, it becomes an issue with the 502 modules with their input sensitivity of 2.7Vrms. The 252 modules are well below 2V sensitivity. Why pay up for the 502 if I won’t be able to drive them to the higher power output anyway?
 

aaddas

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Roksan K3 power amp
115 w / 900mv
Is that good?
 

HarmonicTHD

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Roksan K3 power amp
115 w / 900mv
Is that good?
When just looking at sensitivity there is no good or bad in general. You simply need to know that either you select an up stream device which can deliver the voltage to drive your amp to full power or that you set your power amps gain (where available) according to your up stream device max output capability.

However related to sensitivity there is the whole aspect of “gain staging” where you are trying to optimize for example the total SINAD of your device chain by setting the gains (sensitivities) of the various stages accordingly. Simply speaking it often pays off to maximize the output voltage of the upstream device and minimize the gain (lower the sensitivity) of the downstream device. But one would have to look at the specifics of each device to really tell and give a recommendation. And even then, nowadays electronics are so good that the optimization might not even be audible.
 

restorer-john

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Roksan K3 power amp
115 w / 900mv
Is that good?

It's perfectly fine.

Power amplifiers have been 1.0-2.0V for full rated output since Adam was a boy. 900mV is typical UK oversensitivity, but in practice it just means you get a little less volume range at the low end.

The unbuffered Hypex and Purifi sensitivity numbers are just silly- don't worry about them. Buffers solve that problem.
 

aaddas

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@restorer-john
Thank you and if you compare roksan k3 vs rotel 1582mk2 ...which one you will go with?
 

restorer-john

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@restorer-john
Thank you and if you compare roksan k3 vs rotel 1582mk2 ...which one you will go with?

The Roksan is a streaming integrated amplifier, whereas the Rotel is just a classic 2 ch power amplifier.

Hard to compare, but if I was being truly honest, I'd rather have the Roksan as it is clearly a very versatile unit.
 

aaddas

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Roksan k3 power amp
 

a2Thompson

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Maybe this will help your understanding:

Audio Power amplifiers are Voltage amplifiers (until they run out of current)
OMG, thank you from the past. I have been trying to understand how speaker impedance across frequencies will impact the volume of sound and wondering what happens when impedance peaks around 30 or 40 ohms and thus the amp would provide much less power to the speakers at that frequency...thinking maybe that means it will fall short, but alas it is voltage that matters first and I think based on what you said, at 30 or 40 ohms it will be easy for the amp to provide the necessary voltage and current, whereas at that same speaker's low impedance point (say 4 ohms) providing the same amount of voltage will require a lot more current and the amp might not be able to do it and so...clipping? In that case, as long as you've got an amp to drive enough power to the lowest impedance across the frequency, you're good to go? Everything above that would be "easier" and not cause clipping at the same voltage?
 

DVDdoug

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providing the same amount of voltage will require a lot more current and the amp might not be able to do it and so...clipping? In that case, as long as you've got an amp to drive enough power to the lowest impedance across the frequency, you're good to go? Everything above that would be "easier" and not cause clipping at the same voltage?
Right... If it can't supply the current, it can't supply the voltage so clipping will occur at a lower voltage. Typically, we are measuring/monitoring the voltage (and the distortion) in the voltage waveform because it's easier to measure voltage than current.

At a given resistance/impedance, voltage and current are directly proportional (Ohm's Law) so both are clipped/distorted.

In the real world, the capacitors in the power supply temporarily store energy and they can momentarily supply "extra" current on musical peaks. So if the amplifier is "current limited" it will probably perform better with music than what's indicated by the continuous power rating. And you'll only get occasional maximum-output at the frequency where speaker impedance is lowest. Some manufacturers publish a "peak power rating", but there are no standards for that and there is a lot a variability in program material so It's not something I'd rely on.
 
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