This is my first post here, but I have been following discussions here and on the old forum for quite a while. This is a great place.
Thanks a lot for the B-Pre schemo. I have one, too, and I quite like it.
Theres one minor mistake I found: the pot next to the gain control is actually 1000 u. You might have mistaken it for 100u, because it is very low voltage and therefore relatively small.
The 2SB737 is obsolete, unfortunately. I talked to a designer for another German audio company, who said he was quite fond of that particular transistor. The usual replacement is 2SA1084.
On my unit I paralleled the electrolytics with .1 u WIMA polyester caps, which improved the sound a bit (more transparent).
Thanks for the info on the diodes. So changing them for a better type would improve noise? Would be a cheap and simple mod. My unit is pretty low noise already.
Another thing that I'm wondering about is the opamps. Back then B used the BE 027 and BE037 dual and quad opamps. In an old broshure they even advertised them as higher quality replacements for standard opamps such as TL07x and (I think) even NE5532. I still don't know what exactly those opamps were. I asked B several times, but they never replied. Given the high quality claim I always assumed they must be significantly better than a lame LM348. I know that there is a B-parts list somewhere on the web that suggests LM348 or something similar, but I don't think that's what they actually were. I have a couple of Composers that use different opamps depending on when they were built: BE027, BA4558, NJM4580. The by far worst sounding of them is the BA4558 one; its sound improved dramatically when I swapped it for a NE5532. The 4580 is lowest noise, but I don't really like its sound. The BE027 one sounds fine to me.
Bottom line: I'm hesitant to replace the BE opamps in my Ultragain 2000, because you can't get the original part anymore, and I'm not sure if anything else is really an improvement. Hey, maybe I'll build a pre according to your schematic for experiments.