Power amp input level

[Binjo]

This feels like a dumb question, but I've pretty much finished designing my forthcoming B.E.A.N.S. amplifier, and just putting the finishing touches before I post it here.

So far, my amp design just has a fixed gain of 20 (26dB) so needs 1.42V pk for 50W into 8 ohms.

What is a normal line level input for a power amp? I've looked around and there seem to be different standards. What is normal for a hi-fi amp?

Also, I may not know much about amplifiers, but I saw a picture of one once, and it had a big volume knob on the front, so I'm guessing the amp can accommodate a range of levels. My design doesn't include one but I suppose if it ever gets built then it might need one.

 

[as_audio]

The gain you have is pretty standard.

 

[ron68]

You might need some additional gain to excite this amp from consumer line level -10dBV in order to achieve maximum power.
Specially if you have good recordings that don't go to the digital limit close to clipping.

See the wiki:

https://en.wikipedia.org/wiki/Line_level

I would not change the power amp gain, but I'd just add an opamp before with the additional gain.

 

[Binjo]

See the wiki:

Funny I read that wiki earlier! Reading stuff is useful, but always good to have some experienced opinions too.

I would not change the power amp gain, but I'd just add an opamp before with the additional gain.

Yes that seems sensible, and gives a nice low impedance for the LTPs to avoid bumps in the response and a good place to insert input filtering and put a big fat volume knob.

Thanks for your help. I guess I don't need to change anything at this point, which is nice.

 

[availlyrics]

I would not change the power amp gain, but I'd just add an opamp before with the additional gain

Agreed
Signal chain shoud be as follows - gaIn opamp - volume pot-buffer opamp-power amp
You can then have input sensitivity like, say 300 mV instead of 1.42V

 

[MarcelvdG]

There is very probably no need for 300 mV input sensitivity. That -10 dBV for consumer equipment is a nominal RMS level, the levels in the loud passages are almost always considerably higher. (That 1.42 V is a peak value, so it would usually be called 1 V because of the strange habit of audio people to specify everything as sine wave RMS values, even when there is no sine wave in sight.)

 

[availlyrics]

300 mV i/p sensitivity is good for connecting mobile phones while 1.42V would be compatible with consumer CD players or DAC

 

[Binjo]

Agreed
Signal chain shoud be as follows - gaIn opamp - volume pot-buffer opamp-power amp
You can then have input sensitivity like, say 300 mV instead of 1.42V

Thanks, that video certainly clarifies things for me.

There is very probably no need for 300 mV input sensitivity. That -10 dBV for consumer equipment is a nominal RMS level, the levels in the loud passages are almost always considerably higher. (That 1.42 V is a peak value, so it would usually be called 1 V because of the strange habit of audio people to specify everything as sine wave RMS values, even when there is no sine wave in sight.)

300 mV i/p sensitivity is good for connecting mobile phones while 1.42V would be compatible with consumer CD players or DAC

Good points. Well it's clear now that a pre-amp will be another part of the project to design later, and for now I can just concentrate on finishing the power amp proper.

 

[jeannot60]

From what I've seen so far, amps are designed to deliver their full power with between 750mv and 1V rms input.
So the more powerful the amp, the more gain it needs to achieve that.

 

[anatech]

Average amplifier gain is 28 to 34 dB, they can range down to 22 dB and up a touch higher. 20 dB is unusually low. Whatever that works out to in signal level. There is no real standard, so just be reasonable.