Amp clipping technical question

[1shane5]

Hello guys first post here,

I'm trying to gain a better understanding of what causes amp clipping. Not how to avoid it or anything practical, but a more theoretical understanding.
The more i look into my question the more I realize how uncomfortable I am with electrical theory. But here's the core. Say I am playing music from my phone into the back of a stereo receiver. Some songs are louder or quieter than others based on mixing/ mastering. If I turn up the volume knob on the quieter track until it is as loud as the other track am I pushing the amplifier closer to clipping/asking for more power?

That's how I always thought of it, but now that I'm looking at getting separates as opposed to something like an integrated amp I realize that the amp is basically always the same; it's either on or it's off. This leads me to want to re-frame my understanding that the aforementioned example would be incorrect because turning up the volume knob is just feeding a stronger signal into the amp.

Adjacent to this is wondering if with a passive preamp the output is essentially 1:1 at the highest volume knob position.

I appreciate anyone who takes the time to look at this. I've done my fair share of googling to try to get an answer for myself, but feel like a need an EE degree to understand some of the responses.

 

[DonH56]

Short overview of clipping: https://www.whatsbestforum.com/threads/clipping-101.8484/#post-147098

@amirm -- Did not see this article here? If not, I should clean it up and post it again, I guess.

To answer the question, if the volume is the same at the output, then the output amplifier is delivering the same power to the speakers no matter the input level. If the input is louder, you could be clipping the input stage, but I really doubt it.

Yes, most passive "preamps" are about 1:1 at max volume.

HTH - Don

 

[RayDunzl]

I'm trying to gain a better understanding of what causes amp clipping.

An amplifier takes a varying input voltage (music), and ideally, outputs a voltage that is a (usually) fixed multiple of that input voltage.

However, the output voltage is limited in the level that can be output. Generally, the higher the wattage rating of an amplifier, the higher its output voltage limit,

If you input too much, the output hits its ceiling, or floor, or both. The music signal swings between positive and negative voltages.

---

Other conditions can cause clipping, but this is the most basic.

---

My amplifier claims 26.4dB gain.

That's a multiplier of 20.89

Whatever voltage is input is multiplied by 20.89

.01V signal level in, 0.2089V out

.1V signal level in, 2.089V out

1V signal level in, 20.89V out

10V signal level in, 208.9V out. Oops, it can't output 208.9V. That signal will clip at the limit of the amplifier output stage..

The maximum input voltage specified for this amp (the "sensitivity") is 2.34Vrms.

The maximum output voltage is specified as 49Vrms

Sensitivity x gain factor
2.34 x 20.89 = 48.8V

---

Say I am playing music from my phone into the back of a stereo receiver. Some songs are louder or quieter than others based on mixing/ mastering. If I turn up the volume knob on the quieter track until it is as loud as the other track am I pushing the amplifier closer to clipping/asking for more power?

No, more like "the same" power.

(exceptions can apply)

Turning a volume knob increases/decreases the signal sent to the amplifier stage.

In your example you are matching input signal levels, to create similar output levels.

 

[Zedly]

I've had a similar question. Suppose I have the following situation:

Song A is mastered so that -25 dB on my receiver/amplifier dial outputs 75 db SPL from my speakers.
Song B is mastered at a lower level, so to get 75 dB SPL from my speakers, I have to turn my receiver volume up to -16 dB.

Is my receiver using more power when I play Song B? It seems like the speaker shouldn't be drawing more power, since the SPL is the same. But there is the rule that 3 dB of amplifier gain requires double the power, so the 9 dB increase in output would require 8 times the power. Which is correct?

 

[RayDunzl]

Song A is mastered so that -25 dB on my receiver/amplifier dial outputs 75 db SPL from my speakers.
Song B is mastered at a lower level, so to get 75 dB SPL from my speakers, I have to turn my receiver volume up to -16 dB.

Is my receiver using more power when I play Song B? It seems like the speaker shouldn't be drawing more power, since the SPL is the same. But there is the rule that 3 dB of amplifier gain requires double the power, so the 9 dB increase in output would require 8 times the power. Which is correct?

You are increasing the input of B to match A.

So, all things being equal (which they never are) the final output levels are the same.

Consider the case where you make a copy of a tune, and attenuate the copy by 16dB.

If you play the copy 16dB louder, you are back where you started.

---

If the quieter song has peaks near 0dB, you'll get clipping if you turn it up too far:

Here is a quiet section of a symphony after a peak that can't have its volume turned up (if it was already near the amplifier limits)

Amplified by 16dB and severely clipped:

 

[AnalogSteph]

Increasing amplifier gain does not, in fact, require more power. 3 dB higher output level = 2x the power.

So mains power usage would be about the same in both cases, with minor variations depending on crest factor.

 

[1shane5]

Very interesting. Thanks so much guys. So it seems that my old understanding was largely incorrect. Always good to know where the limits of my equipment are and what actually pushes those boundaries.

I really really appreciate all the well thought out responses.

Cheers,

Shane

 

[RayDunzl]

I've had a similar question. Suppose I have the following situation:

Song A is mastered so that -25 dB on my receiver/amplifier dial outputs 75 db SPL from my speakers.
Song B is mastered at a lower level, so to get 75 dB SPL from my speakers, I have to turn my receiver volume up to -16 dB.

Ok.

Is my receiver using more power when I play Song B?

No.

It seems like the speaker shouldn't be drawing more power, since the SPL is the same.

True.

But there is the rule that 3 dB of amplifier gain requires double the power, so the 9 dB increase in output would require 8 times the power.

You matched output levels by adjusting the input voltage. You didn't change the gain of the amplifier.

Which is correct?

https://www.electronics-tutorials.ws/amplifier/amp_1.html

 

[Zedly]

Thanks for the responses. I understand better now.

 

[solderdude]

Amplifiers have physical limits.
There is a maximum output voltage and there is a maximum output current.
As soon as 1 of its limits is reached the output signal 'clips'.
At which loudness (speakers or headphone) this occurs depends on the efficiency of the speaker or headphone.
The higher the efficiency is the louder the system will sound before clipping.
Clipping sounds like a 'roughening' of the sound. It turns 'grittier'. When clipped even further is starts to sound nasty.

The lower the efficiency of the used speaker/headphone the sooner clipping will be heard.

In both the low and high efficiency headphone/speaker, proving the impedance is the same, clipping as a technical level will occur at the same electrical limits (be it voltage or current). independent of the volume control or gain. It's the efficiency of the used speaker/headphone that determines at which sound level (loudness) this happens.

This is why some folks need huge amount of power and others only need a few Watts. It is all because of efficiency. How loud a headphone/speaker goes at a specific output voltage.

This is completely independent of gain (how much amplification is needed) or volume control position.

There are a few exceptions though. A well known one is the O2. This is because the amplifier's input circuit can clip but the output stage may not.
It's still clipping but only in output voltage.