Gain and linestage

In short it works like this.


If the poweramp needs 2v in to get it's rated full power, and you only have 1.5v max at full volume from whatever is feeding that poweramp, then your .5v short of getting the amps full power. But then the speaker has to be able to take it also.
Active Preamps with "unity or low gain", Passive Preamps, as well as source direct, "can" do this.

But if the poweramp only needs .5v in for full power out, then anything before it with extra gain (more than .5v out) is not usually needed.

Cheers George

Good enough.

If you hooked up your amplifier directly from the output of a CD player or DAC you would blow out your speakers. A CD player puts out a signal of  2 volts max  and a power amp reaches full power at about 1.4 to 2.0 volts. That said, a preamplifier with (any) gain would make things much worse. That is why preamplifiers cut the voltage from the source through the volume pot and then gain up that divided voltage out to the amplifier. 

An amplifier can reach full power from a CD source with just a linear volume pot before the amplifier. The only way a preamp can impede that is if it divides the voltage too low through a poorly designed volume control and that has nothing to with preamp gain or amplifier power.

That is why preamplifiers cut the voltage from the source through the volume pot and then gain up that divided voltage out to the amplifier.

That’s like lowering the output of any source, and that’s bad news for noise/distrotion, because then it has to be amplifed back up again noise/distortion and all by the active preamp again. To keep noise/distortion down, you need to use everything the source has got.

Nelson Pass says it well here.

Nelson Pass,
"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."

And yes he does sell active preamps with lots of gain, to those that want to buy them, remember he’s in business to make money.

Cheers George

If I look at the Butler TBD 2250 specs, I see this:
 Input Sensitivity: 2V for 250 Watts into 8 Ohms 
Which I'm sure is the relevant spec to look for on the amp?But for the preamp, what's the relevant spec?  For a Parasound PA6, I see this: Preamplifier Stage Input Sensitivity
300 mV in for 1 V
Total Gain: 10 dB
Max Output: 7.5V Sorry guys.  This one caught me by surprise.  I knew users looked at amp/preamp combos from the "match by sound quality" perspective, but not by this.

Nelson Pass says it well here.

Nelson Pass,
"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."

And yes he does sell active preamps with lots of gain, to those that want to buy them, remember he’s in business to make money.

Or he's in business because he enjoys doing audio. There *are* other possibilities...

he's in business because he enjoys doing audio.

@atmasphere
  +1111111111111111

And then there's this.
https://forum.audiogon.com/discussions/preamp-output-voltage

There *are* other possibilities...

Of course there are, you’d have to be ignorant to think otherwise.
Some others in the industry are hedging their bets on different circuit configurations, when one is going sour no matter how hard they promote/push it, they will have another to fall back on. It's called business, and doesn't make you any less an audiophile.