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Amplifier Input Sensitivity and Voltage Compatibility

Djano

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I would like to benefit from your expertise to better understand a point that is perplexing me. My question concerns the acceptable voltage to send to an amplifier, which, from what I understand, depends on the amplifier's input sensitivity, unique to each model.

Yamaha explains that 'Input sensitivity refers to the input signal level that results in the rated output at maximum attenuation (normally 0 dB). It also refers to the input level at maximum attenuation above which the output is clipped.'

So, to avoid any clipping or distortion beyond the specified limits (which I already know are often quite forgiving), it's advisable that if you want to set the volume to the maximum on the amplifier, you shouldn't provide an input signal exceeding its input sensitivity.

However, if I set the amplifier without ever going beyond 50% (12 o'clock), does that mean that I can send it twice the indicated input sensitivity ?
For the sake of discussion, let's assume that 12 o'clock truly corresponds to 50% of power; I'm aware that the volume potentiometer is rarely linear.
In other words, is it correct to summarize things by saying: [Max. output before clipping] = [Input sensitivity] * [Output gain] ?

If this reasoning is correct, what are its limits? For example, is it safe to send an input voltage ten times higher than the amplifier's input sensitivity if the amplifier is set to only 10% of its power output? This would imply exceeding the line-level voltage, and I can't seem to grasp if that's problematic.

To provide some context, I'm asking this question because my preamplifier seems capable of exceeding 2V, while my amplifier has an input sensitivity of 700mV.
 

sergeauckland

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A volume control potentiometer usually has a 10% log law, which means that at 50% rotation, the attenuation is 90% (i.e. 20dB of attenuation)

Theoretically therefore, you could send 10x the rated input signal to the amplifier without clipping.

However, this requires the volume control to be the first thing the signal hits when entering the amplifier. If there's an input buffer, then the maximum signal is whatever the buffer can take, which can be expected to be lower. How much lower depends entirely on the specifics of the item.

If you're using a pre-amp in front of the power amp then it makes sense to check what the pre-amp's volume control setting is for normal listening levels. As most pre-amps have excessive gain, this means that the pre-amp's volume control is all at the bottom, making fine volume adjustments difficult. If that's the case, then setting the power amp's input volume control somewhere below 100% will allow the preamp's volume control greater range.

As I mentioned, preamps generally have excessive gain, so I normally set my power amps with some attenuation (I currently use 16dB) giving me a wide range on the pre-amp's volume.

S.
 
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Djano

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Thanks for your answer

What you describe seems to be how I do things now: my power amp is set to 25/50% (this is the volume dial, and I do not know if this corresponds to the "power amp's input volume" you are refering to), so that I can have an usable range of adjustment on the preamp.

But my issue is about the fact that my preamp goes beyond 2V. Is that too much for the max. voltage a typical input buffer can take ? Obviously, this depends of the specifics of the item, as you said, but is there an approximation that works for most ?
 

sergeauckland

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Thanks for your answer

What you describe seems to be how I do things now: my power amp is set to 25/50% (this is the volume dial, and I do not know if this corresponds to the "power amp's input volume" you are refering to), so that I can have an usable range of adjustment on the preamp.

But my issue is about the fact that my preamp goes beyond 2V. Is that too much for the max. voltage a typical input buffer can take ? Obviously, this depends of the specifics of the item, as you said, but is there an approximation that works for most ?

I don't think there's any useful 'approximation that works for most' as it depends on too many factors.

However, although your pre-amp can output more than 2V, it probably never will unless you're in the habit of running your pre-amp at 100% volume or your pre-amp has excessive gain for the sources you use. In practice, you'll probably be running the pre-amp at 50-60% volume, so with volume control attenuation of something between 15-20dB the output will be well under 2V. This of course depends on the sensitivity (i.e. gain) of the pre-amp, the output level of the sources and the law of the volume control.

As to the maximum input a power amp buffer can take, that depends on the design, but I would expect any buffer to be powered from +-15v rails, and assuming unity gain for a buffer, this means that it should be able to handle some 7.8V (+20dBu) before clipping,possibly a bit more.

As I said there are many factors that will influence how a pre/power combination works, and the only real ways of knowing is to analyse the circuit diagram and/or detailed specification or measure them. If I were in your situation (which it seems like I am) I use 16dB attenuation in the power amp, and have never been close to clipping the pre-amp or power amp, verified by measurements.

S.
 
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Some amps can be clipped just a bit over the rated input voltage. I've had a power amp (Yamaha) do just that and it took me a while to figure out why it sounded distorted on some bass heavy tracks. I heard it as treble distortion when the bass hit.

So I wouldn't send more than the specified voltage into an amplifier.
 

sergeauckland

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Some amps can be clipped just a bit over the rated input voltage. I've had a power amp (Yamaha) do just that and it took me a while to figure out why it sounded distorted on some bass heavy tracks. I heard it as treble distortion when the bass hit.

So I wouldn't send more than the specified voltage into an amplifier.
No indeed, if it's a power amplifier as the specificed voltage is almost by definition the maximum it will take without clipping. This however has to be viewed differently if the power amp has input attenuators as then the amplifier can take a much higher voltage before clipping. How much higher depends on whether there's a buffer before the volume control and what the headroom in the buffer is. If no buffer, then the input level can be very high, many tens of volts, much less with a buffer, perhaps only 8v or so.

S.
 

AnalogSteph

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if it's a power amplifier as the specificed voltage is almost by definition the maximum it will take without clipping.
For example, let's say you have a power amplifier that can output 200 W into 8 ohms, with a fixed gain of +26 dB.

200 W into 8 ohms is √(200*8) Vrms = 40 Vrms, so when divided by 26 dB = 20 that's an input sensitivity of 2 Vrms.

With such an amplifier, input and output level are directly correlated. (Feed in 2 Vrms, have your ears blown off.) Input sensitivity also pretty much equals maximum input level, as the amplifier will clip shortly above its rated output.

If you were to add a passive input level trim (volume control) to the input of such an amplifier, this would decouple the two. Input sensitivity would remain the same, still determined by power amplifier gain, but maximum permissible input level would increase depending on how much the volume pot is turned down, ultimately being limited only by the pot's permissible power dissipation (so generally >10 Vrms).

The more "stuff" there is in front of the actual power amplifier, the more complex it potentially gets. You might have the volume pot preceded by a balanced receiver that can only take so much input depending on its supply voltages, and in lots of integrated amps / receivers you'll be seeing input selector / volume / tone control / preamp PGA ICs that can generally take 2-3 Vrms (it would be a bit silly if you couldn't connect a typical CD player with a 0 dBFS output in the 2-2.5 Vrms range, plus a bit of headroom for intersample-overs).
 
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Djano

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Thanks you all. So, I believe I understand that:
  • The input sensitivity can, in principle, be exceeded as long as there is attenuation (external or internal) to ensure that the output power does not exceed the initial rating.
  • However, it's important not to exceed approximately 8V if there is an input buffer to avoid clipping that would occur for this reason alone, even if the rated output power is not exceeded.
  • That said, if attenuation occurs upstream of the buffer, you can once again exceed 8V, provided that the attenuation brings it back below that level.
Does this sound accurate to you?

I have another question as a result. The specific implementation of the volume control potentiometer (which I take as a synonym with attenuator, please correct me if this is wrong) is crucial in your responses. I'm not entirely clear on the various possible scenarios. Is the volume control likely to come before the buffer, after it, before amplification, or after amplification? Or, once again, does it depend on the specific choices made for each model?

_______________________

HOLDT: Some amps can be clipped just a bit over the rated input voltage. I've had a power amp (Yamaha) do just that and it took me a while to figure out why it sounded distorted on some bass heavy tracks. I heard it as treble distortion when the bass hit.

So I wouldn't send more than the specified voltage into an amplifier.

When that happened, did the amp run without any attenuation, or it happened even with attenuation ?
 
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Thanks you all. So, I believe I understand that:
  • The input sensitivity can, in principle, be exceeded as long as there is attenuation (external or internal) to ensure that the output power does not exceed the initial rating.
  • However, it's important not to exceed approximately 8V if there is an input buffer to avoid clipping that would occur for this reason alone, even if the rated output power is not exceeded.
  • That said, if attenuation occurs upstream of the buffer, you can once again exceed 8V, provided that the attenuation brings it back below that level.
Does this sound accurate to you?

I have another question as a result. The specific implementation of the volume control potentiometer (which I take as a synonym with attenuator, please correct me if this is wrong) is crucial in your responses. I'm not entirely clear on the various possible scenarios. Is the volume control likely to come before the buffer, after it, before amplification, or after amplification? Or, once again, does it depend on the specific choices made for each model?

_______________________



When that happened, did the amp run without any attenuation, or it happened even with attenuation ?
The issue is not connected to the attenuators in front but rather the amps input didn't like 2 V input signal as it was specced to 1.2 V. I could distort the sound via the preamp through the inputs regardless of the attenuators position.
 

DonH56

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This thread is a somewhat detailed look at how attenuation/gain, distortion, and noise can vary through a system. There are some pictures of where volume controls can land in the signal chain. It is a lot to wade through but may be helpful. If you do, I would suggest asking questions here (and not there), both to keep that thread a little more focused, and to make it easier for you to get and follow specific answers about your own system as you have been.

 
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Djano

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This thread is a somewhat detailed look at how attenuation/gain, distortion, and noise can vary through a system. There are some pictures of where volume controls can land in the signal chain. It is a lot to wade through but may be helpful. If you do, I would suggest asking questions here (and not there), both to keep that thread a little more focused, and to make it easier for you to get and follow specific answers about your own system as you have been.

Thanks for this reference, this is huge work.
Will read it tonight !
 

DVDdoug

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Most amplifiers have more than enough gain and most preamps, DACs, CD players, TVs, etc., have plenty of output so that "everything works fine together".

But Line Level is rather loosely defined & controlled and consumer line level is lower than pro line level so sometimes a pro amplifier doesn't have enough gain with driven with a consumer device. Most pro equipment also uses (or can optionally use) balanced connections.

The general "best practice" is to keep the signal as high a possible through the chain, for the best possible signal-to-noise ratio, and then attenuate at the last possible point (usually the output of the preamp/device or at the power amplifier input) to lower the signal and noise together. Then you only have to worry about noise generated by the power amplifier itself.

But, there are often practical or convenience considerations... Some power amps don't have a "gain"/volume control, or often they have separate left & right adjustments, and almost never a remote control. And most stand-alone DACs don't have an analog volume control at the output.

I have another question as a result. The specific implementation of the volume control potentiometer (which I take as a synonym with attenuator, please correct me if this is wrong) is crucial in your responses.
That's correct. The potentiometer is used as an attenuator. A "regular-old" volume control is a pot. A stereo volume control is two pots connected together.

However, it's important not to exceed approximately 8V if there is an input buffer to avoid clipping that would occur for this reason alone, even if the rated output power is not exceeded.
8V is just a "typical example". In most cases the input goes directly into the volume control (perhaps through a capacitor) so the buffer comes later and the pot goes (nearly) down to zero and the pot can probably withstand 50V or so before it overheats. But at that point, with the volume control nearly zero, it's hard to adjust the volume. ;)


That said, if attenuation occurs upstream of the buffer, you can once again exceed 8V, provided that the attenuation brings it back below that level.
No. If the buffer is clipping the audio is clipping and lowering the volume/voltage later doesn't help.
 

Kimbrough Xu

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According to my knowledge, the input sensitity can be vary with power supply, if an amp has a fixed gain such as 26dB, then the amplification can be 20, so if you give a 1V signal to the amp, the output voltage can be 20V.

Under this circumstances, if you power supply is 32V, you can not give more than 1V signal to the amp, otherwise it will clipping; but if you change to a 48V power supply, then you can send a signal more then 1V (can be as high as 1.5V) to the amp, and the output voltage can be 31V without clipping.
 

Kimbrough Xu

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Yes, I mean with the power supply changes, you can put different input voltage to the amp without clipping.
 
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