What do I hear? Impedence at work or just diff between pres?

[MeatBallRagu]

Hiello tou you all:

I racked :
vintage 1272 following JML suggestions ( I really think it's ok).
2 API 312
2 wardbeck
warious home brew pres,

built a cienmag xfo DI according to jesen plans

usign a '76 pBass, I compare the Neve 1272 to all the other, including 737sp and LA-610.

Always PBass to DI to Mic in of pre under test to ISA428 converter,.

I wonder why: N1272 and and UA-610 have (way) more hi freqs than others (all eqs bypass on all machines of course)

TW: we're talking here about nice HFs,

Thanks for your answers guys,
Bye the way I'm quite new here,
You can look at my face and decide your want to answer or not:
www.OreillGauche.com

 

[tv]

IME impendance has a huge impact in passive bass world. That's why I don't like ready-to-go solutions a-la bartolini, emg, mec, because they are only a compromise (bartolini being in particular fitted to bartolini pu's impendance).

IME each passive bass pu/pu combo has a narrow window (cca 5% diff) around it's ideal impendance match (from a preamp or a built-in buffer).

If you know how to build one for yourself, take a look @ peavey microbass schematic:

http://www.freeinfosociety.com/electronics/schemview.php?id=638

replace the 4588 chip with a MC33078 (TL072 will work as well), R1 with a 10K trimmer, R2 with a 500K trimmer, C17 with a 22uF elco (possibly C8 as well !! ), R18 with a 10K pot and use it as the "output" - line/unbalanced. (Omit everything after R18 and build a nice regulated power supply.)

after you are done with trimming to your bass' "best tone", measure and replace the trimmers with actual resistors. You may as well experiment with the tone stack.

voila.