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How important is the pre-amp?

Hello all,

Genuine request here for other's experiences.

I get how power amps can make really significant changes to the sound of a system. And of course speakers have an even bigger effect. And then there is the complicated relationship between the speaker and power amp. But I wonder about pre-amps.

In theory a well designed preamp should just act as a source switch and volume control. But does it add (or ruin) magic? Can a pre-amp color the sound? Alter pace and timing? Could you take a great sounding system and spoil it with the wrong preamp? Stereophile once gushed (while reviewing a preamp that cost as much as a car) that the preamp was the heart of the system, setting the tone of everything. Really? Some people don't even bother with a preamp, feeding their DACs straight into the power amp. Others favor passive devices, things without power. If one can get a perfectly good $2K preamp, why bother with 20K?

What your experiences been?
128x128rols
unsound
7,336 posts
 
Addendum; Another consideration would be to include volume controls at the input of the amplifiers (this would probably require remote control) so that full output would be driving the full length of the cables.
And yet another consideration would be, at least for Class D amplifiers, to have digital inputs. From which a conversion of PCM to PWM would take place, and thus eliminating the traditional DAC altogether.
georgehifi's avatar
georgehifi
10,312 posts
 

Many amps are 1.5v or less input sensitivty for full output, and most dacs today are well over 2v output these days, so there's no problem with being able to voltage drive.
And most dacs today have very low output impedance output stages, that are equal to or better than many solid state preamps to drive any capacitive interconnects with, essecially bettering most tube preamps.
So it's a furphy to say a preamps drive better than dacs can direct.
 And like I said if a passive pre has no voltage or impedance issues then it is the next best way. 

Sure balanced has it's place in over 3mt interconnect runs, for noise cancelation only, below that there is no need for it. As single ended is just as good, and better in many cases better, as the balanced inputs of many poweramps are just a "balanced opamp" then leading the into the real single ended input of the amp which will sound better.

Cheers George
schubert
7,386 posts
 
If you listen to rock pre-amp means about 2%.

If you are into Jazz about 70% .

In Classical 99% .
atmasphere's avatar
atmasphere
11,979 posts
 
@unsound  You really do have to wonder what the designers of Redbook were thinking. In all cases of a Redbook output driving an amplifier, the voltage has to be knocked down, often quite a bit.
Many amps are 1.5v or less input sensitivty for full output, and most dacs today are well over 2v output these days, so there's no problem with being able to voltage drive.
-And this is false for the simple reason that there is a problem when you knock the signal level down. If a passive device is used, its an impedance that sits between the circuit driving the interconnect cable in the source, and what is being driven (the amplifier). That is why passive volume controls are so sensitive to cables: they are about as high an impedance as you can have for driving the cables and so are far more sensitive to the vagarities all cables have.


IMO/IME its a pretty poor line stage that can't outperform (and by that I mean be more musical and more neutral) a passive volume control. Put another way, if the passive seems better then line section you're using for comparison isn't all that great to begin with.



georgehifi's avatar
georgehifi
10,312 posts
 
If a passive device is used, its an impedance that sits between the circuit driving the interconnect cable in the source, and what is being driven (the amplifier). That is why passive volume controls are so sensitive to cables:
This is false.

To explain to members with the maths of it.
As a 10kohm passive has an outuput impedance of around 2.5kohm, the "cheapest interconnect cables" can be <100pf capacitace per ft and less. It would if be use you 2mts!! of it, still be only 300pf!!!
And this 300pf capacitance with the passives 2.5kohm output impedance, will still only be only -3db down at 212khz!!!! in hf rolloff, a dog would have trouble hearing this.

And that’s why it’s false info to post and say passive pre’s are cable sensitive, sure to a dog or bat maybe!!.

Cheers George
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