bill@vrdxhq.verdix.com (William Spencer) (12/10/90)
I said: > 2. BI-AMPING. Note that reducing C3 and R8 in the preamp gain stage above >[...] A Radio Shack equalizer provides a known > constant load to the passive low pass section (RS includes schematics. Note that this arrangement is a bit noisy. With a solid-state preamp driving the low pass filter, a lower impedance filter can be used for better results. Or a better buffer could be built. > I presently am using a seperate phono preamp. > I may go to the seperate preamp and bypass the preamp section entirely. Tried this. Main improvement is the bass. I have a theory: It's not the tubed preamp circuit that causes the "tubey" bass, it's the power supply. Same thing was true with bypassing the phono stage, although I think it rolled off the highs also. A better supply will help any preamp, but in this case the power stage supply is not seperate, so filering becomes entirely inadequate. I haven't decided about the highs yet. The tube preamp was extended and clean in the highs. The preamp I am using _may_ add a transistor-y sound (pioneer C-21). Our moderator suggests feeding back the secondary into the power tube's cathodes. The 4 ohm tap becomes the secondary ground; the 16 ohm and 0 connections become balanced. Audio Research uses a form of this most interesting circuit. bill S.