Gain of line preamplifier

These days with sources giving out 2v or even more with low output impedance, and amps only needing 1.5v or less for full output. There is no need to do any preamplifying.

All you need is a passive volume control with a unity gain buffer after it if the amp has unusually low input impedance <33kohm, or your driving 10mt of interconnect.

Or a 10kohm passive pre if the amp has >33kohms or more input inpedance, with up to 1.5mt of good interconnect.

And if you don't believe me.

A Quote from the master Nelson Pass

"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."



Cheers George

"Variable output impedance is "heavy disadvantage" of any passive preamp even if you have substantially high input impedance of your amplifier."

Wrong Czarivey, ^you stated^ and the reason is.

A 10kohm passive can have a varying output impedance, at it's highest (worst) it's 2.5kohm at mid position.
Any amp/s that have input impedance 47kohm and especially higher will have absolutely no ill effect on the sound with 47kohm it's close to 1:20 impedance ratio. And if 100kohm input impedance the ratio is then 1:40 ratio. And if the volume is lower or higher than mid point, the ratio/s are even higher, still with out any effect.

The only thing that needs to be watched is interconnect cable capacitance that can cause a HF filter.
The HF filter caused by the interconnect capacitance and this high 2.5kohm output impedance. (BTW: same goes for many tube preamps as well as they can be that high or even higher)

If we look at a bad quality interconnect cable that has 200pf per foot of capacitance, that equates to say 600pf for a meter. This combined with the 2.5kohm of the passive pot will give you a -3db at 106khz! Well beyond our hearing.
All good quality interconnect that I have measured are below 100pf per foot, and this equates to -3db at 212khz! Up in bat hearing territory.

There's just some of the math on this without any voodoo.
I ask once again show the math without the voodoo to counter this if you can?

Cheers George

Like I asked, show the electronic math?

And then post a link to a "quality" interconnect that has high capacitance more than 200pf per foot. And I'll show you a rubbish interconnect?
Because it will create HF filter with tube preamps as well as passive pre's. And the HF audio band filter that it creates is detectable with just listening let alone using math or bench tests.

Cheers George

"Nelson Pass would also agree with me"

If that's not putting words into Nelson mouth, I don't know what is.

Cheers George

"Variable output impedance is heavy disadvantage of any passive preamp even if you have substantially high input impedance of your amplifier."

Please give your reasons why (using laws of electronics)

1: If using a low (<100ohms) source impedance (which most are).

2: Into a 10kohm passive pot with 1mt of low capacitance interconnect (which most good ones are).

3: Into a power amp with 47kohm or higher input impedance (which most are)

"Nelson Pass would also agree with me."

Your assuming a lot with this bold statement, quoting words that Nelson Pass has never made. In which he's been quoted to say the opposite 6 posts back.

Cheers George