don't understand volume control "gain budget" in teemuks book...

[narodo]

Hey guys,

This is my first post, so first of all hi everybody.

I am reading through teemuks excellent book at the moment.
But I found something I don't understand.

In the "practical design example" section on page 286 ff we find the following:
[..]
Let's  say  we  want  to  have  a  volume  control  potentiometer  in  front  of  the  power
amplifier  and  that  we  want  to  get  the  full  output  power  when  the  potentiometer  is
dialed  to  "5". 
[..]

Why would we want to do that?
In that case, would turning the potentiometer to 10 not completely overdrive the power amp and drive it into distortion?
Or is this meant to leave some room at the bottom in case the input signal is weaker than 40mVpeak?

I have the feeling I miss something very basic here.

Thanks in advance!

[teemuk]

would turning the potentiometer to 10 not completely overdrive the power amp and drive it into distortion?

Yes.

Or is this meant to leave some room at the bottom in case the input signal is weaker than 40mVpeak?

If I understood what you meant with that correctly, then yes.

Basically, the idea is getting the full output power without having to dime up the amp.

[narodo]

Cool! Got it!

Thanks Teemuk for the quick reply!

[joecool85]

would turning the potentiometer to 10 not completely overdrive the power amp and drive it into distortion?

Yes.

Or is this meant to leave some room at the bottom in case the input signal is weaker than 40mVpeak?

If I understood what you meant with that correctly, then yes.

Basically, the idea is getting the full output power without having to dime up the amp.

Is there any down side to getting full power at 10?  I would actually like my amp to do that.  Seems like it makes sense.  Then I can get my distortion from the OD circuit or a pedal.  Meanwhile, my Dean Markley doesn't really get any louder after you get past 5-6.  So why even have "10"?

[teemuk]

Well, consider the following scenario:
An amplifier is configured to produce its maximum output power with input signal amplitude of, say, 40 millivolts - or something rather standard along those lines. Now, you bump into a device (guitar, effect pedal, whatever) that actually can't output no more than 20 millivolts. Since the amp is configured to produce its full output power when volume control dial is set on "10" you don't have any reserve left to compensate for the weaker source signal. So....

Not to mention, there are many examples of solid-state amps benefitting from slight power amp overdrive too.

[rowdy_riemer]

I've pegged a TDA2040 before and liked how it sounded.