impedence value.? amp to preamp.

What you need to look at is the input impedance (the higher the better) of the power amp and the OUTPUT (not input) impedance (the lower the better) of the preamp. The common consent is at least 10 to 1 ratio, i.e. you need the input impedance of an amp to be at least 10 times higher than the output impedance of a preamp.

Both Sidssp and Tvad have fairly well hit the nail. FWIW many tube pre-amps have a 600 ohm output impedence (my ARC SP10 does, and recommends a minimum amp input impedence of 20K ohms). As common are some with output impedences of 3500 ohms. (Three other tubed pre-amps I have have output impedences of 3500 ohms.) None of them really sound all that good with amps with less than 47K input impedence and one even likes 100K best.

Tvad's comments about impedence being a moving target is right on, and you need to start by knowing the output impedence of your Bottlehead (I tried to look it up but couldn't find it).

FWIW.

problem is iam not using my bottlehead.i am considering a passive pre. but i cant afford bent, sonic euphoria,canary ect.

Passive pre-amps/attenuators etc also have output impedence, usually varible, and require very careful IC matching to get a good result.