Krell amps and Tube Preamps - enemies?


Wow! I never realized how difficult it would be to add tubes with a KRELL amp. I'm no engineer, and, I don't pretend to be into the "technical" side of the audio world. So I'll try to explain.

It seems that tube Preamps create DC. I've been told that DC will dammage my Krell amp (FPB400cx), and possibly my speakers(Tyler Acoustics Linbrook Sig, System 1 piece). UNLESS, I open the amp up and do something to the "jumpers on the digital board" . This puts some protection into the signal path. The Bad thing is, I'm told, - it also colors or degrades the audible signal coming thru the speakers. So, if I want to use my SS set up, say for SACD or DVD-V/DVD-A, I would have to open the amp up again and reverse the proceedure. This would remove the "blockage" in the signal path. :-( This of course, would have to be re-done when I want to go back to the tube setup. WHAT A PAIN!

Needless to say, this has thrown the proverbial 'wet blanket' on my tube enthusiasm. Is this problem common to ALL SS amps? Or is it just a KRELL thing?

Any thoughts would be helpful.
(This is part of a thread i started on the speaker threads, but i thought i might have more luck here on the "amp' Threads)
Thanks
oldpet

Showing 4 responses by john_tracy

I just finished building and "burning-in" a Raleigh Audio line stage kit that was featured in a series of articles in AudioeXpress magazine. The circuit was in part inspired by an article on parallel feed circuit topology by Lynn Olson that appeared in Vacuum Tube Valley. The relevance to this thread is this: it is transformer coupled on the input and output with Lundahl amorphous core transformers. If you haven't heard these trannies, don't let any pregedices you may have for transformers close your mind to this option. These amorphous core transformers have "magic" in them. And more to the point, no DC in output. Also, all your components will be galvanically isolated from each other. Since I have inserted this component into my system I have noticed a real lowering of the noise floor. This is one of the most open, realistic and revealing preamps I have ever heard. If you are looking for "natural presense" and "holographic" imaging check this preamp out.
Oldpet - log on to: www.kandkaudio.com or check out the K&K Audio sponsored forum over on the AudioAsylum. There was also a series of articles published in AudioXpress by Dave Davenport under the title "A Line Stage Odessy". A very complete kit is available for $1799 which is what I purchased and built. The kit has 6 inputs (one XLR, 5 RCAs with one of the RCAs a fixed volume one for HT cinema use), remote volume and mute and two outputs, XLR and RCA. The only change that I made was to substitute Cardas caps for the supplied Kimber parafeed blocking caps.
Oldpet - I purchased the RA line stage as a kit which requires doing all the soldering. Most of that is to PC boards and the instructions are very complete. If this is a problem, it is available already built. I now have over 350 hours on mine and the sound has continued to improve. My experience with the Lundahl transformers in my K&K phono preamp is that they will continue to "sweeten up" over several hundred hours.
Oldpet, the bass is just fine. The preamp is transformer coupled; it can't leak DC. Also, since it is a differential parafeed design, there is no DC at the input of the output transformer. That is how they are able to use a high quality mike input trannie wired in reverse for that job. These transformers will not tolerate any DC on their input.