impedence value.? amp to preamp.

With a 15kohm input impedance, I would look at an output impedance of 200
ohms or lower, if possible. 15kohm input impedance is on the low side.

Personally, I think the 10 to 1 ratio is too low. When matching for my system, I
now look at a ratio of at least 50 to 1 in order to not have rolled of bass or
treble.

Keep in mind that amps and preamps do not have flat impedance curves. A
preamp with a rated output impedance of 200 ohms can easily have impedance
spikes well above 1000 ohms, and two preamps with nominal 200 ohm output
impedance specs can have wildly varying impedance spikes. Therefore, IMO
the value of the impedance spike should be carefully considered...even more so
than the rated output impedance...when matching gear. John Atkinson's
Measurements section of Stereophile equipment reviews is very helpful when
examining a component's impedance curve.

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.