Hi, yes I have one, had it for years but didn't use it much. Just never sounded that great to me (more in a minute). Here's a link to the Carvin Museum site about it:
The Carvin Museum - 1990 PB-15 Bass Preamp
Was also basically the same preamp in all the Carvin Pro Bass amps in the early 1990's (PB300, 500) but without the graphic EQ.
Doesn't seem to get too much love or don't think many folks have one.
About a year ago I happened across a review by someone who did some measurements and dissected it and found one particular thing that was interesting.
BGRA: Review of Carvin Pro Bass 15
Carvin has what it calls a "mudcutter" circuit (it's in the manual should be a PDF somewhere on the web that has the schematic as well) which is really a 600Hz fixed, non-defeatable
notch filter after the first stage of the preamp. So no matter what you do, it will always have a scooped sound (mudcutter?). He defeated it by soldering a jumper wire on the PCB.
I got mine cheap ($95 IIRC) so I said what the heck, I tried it. Holy crap, the sound opened up after I did that and actually sounded pretty darn good (also been playing around with it and a Carvin DCM1500 into a nEARful cabinet). I decided to put a little toggle switch on the front panel instead of a permanent jumper. I also changed out a few of the op amps (the originals are the cheapest you can find, basically dual 741's which are considered junk by today's standards, but hey they work), with TL072's which while not state of the art (they are used in the Eden WT series amps) are a big improvement of the originals in terms of getting rid of some of the noise. Out of the box this preamp can be kind of hissy with the treble boosted.
I would say, as the reviewer stated, if you can do a bit of soldering and MAYBE if you want to get the noise down by replacing some op amps (they are cheap and just plug in, no soldering for those), then it's worth a shot if you can get it really cheap (less than $100). Otherwise I'd pass on it.
