How much do I need to spend to get a preamp that sounds better than no preamp?

Believe Nelson Pass, his creds far outweigh anyones here.

I believe he says below the input impedance is 20kohm, and states it in the specs, also 99% of sources will drive that, just some silly (pitiful as he says) dac’s ect that have high output impedance, tube buffer stages may not.

Pass Quote:
" Input impedance, the Aleph L is a nominal 20 Kohms. From the standpoint of input impedance, I can only say that it is a very pitiful source that cannot come up with the 100 micro-amps of current needed to drive this input."

Cheers George

Source output impedances in the typical range of about 100 - 500 ohms should easily drive preamps with input impedances of 10K or up....as long as the cables are kept reasonably short.  However, it must then be considered what happens between the passive preamp and the amplifier, how long are the cables, and what is the input impedance of the amplifier?  All of these are factors contributing to the successful use of a passive preamp IMO. 

 I believe it is to simplistic to simply say that if you have enough voltage and reasonable impedances, then a passive will sound good.  I have heard it go the other way too many times.  Based on comparisons between passives and my unity gain buffered preamp, the active buffering (but not necessarily gain) does lead to improved dynamics and bass, even when voltage and impedance rules are met between partnering equipment.

However, it must then be considered what happens between the passive preamp and the amplifier, how long are the cables, and what is the input impedance of the amplifier? All of these are factors contributing to the successful use of a passive preamp IMO.

Nelson Pass addresses this also, as I have always said with the Lightspeed Attenuator passive, interconnect to the amp should be good quality low capacitance, which nearly all are, use <100pf per foot at 2mts or less.

Nelson Pass quote:
"The output impedance needs to be low enough to drive the capacitance of a reasonably long cable. How low does it need to be? I would say that it should be able to drive a 1000 pF load out to 100 KHz.
The worst case output impedance of the Aleph L will drive 1000 pF with a -3dB rolloff at 225 KHz!!."

Cheers George