MC402 vs FPB 300cx

I think you might be right, and if nothing else it's the path of least resistance first. I am actually anxious to try the Auditorium 23's as they are supposed to great for the money. I guess you could say 8tc is not quite up to the task of this system now, I was just hoping not to get sucked into the expensive speaker cable trap again. But heck, if it works I am game.

I gotta tell you though, the detail and smoothness, accuracy, and speed, bass response, silence, and soundstage is everything I expected in this amp. In that respect I love it. In fact the soundstage changed enough that I had to re-toe my speakers to compensate. But...I won't completely head over heels in love with this new Krell like I was my old Krell until I resolve the glare.

My ultimate fear is that this Krell is not for me, and have to go with another amp. That would be a chore and half.

How do you like your Pass? Nice choice.

Krell is recommending capacitively coupling the amp to resolve the glare issue-FPB is direct coupled of course. Something they recommend to do with Tube Preamps regardless, which I have. The KAV I owned before this FPB comes from the factory capacitively coupled. I personally think this is not the answer in trying to resolve sibilance, but the only thing that is compelling me to do it is the fact my KAV sounded great. Alot sweeter. If adding a capacitor into the signal path will change sibilance I will do it, but given the fact there already about 500 Caps already in the path, I have my doubts that adding one more will do much in softening glare.

Working in steps, taking deep breaths trying to be patient as I go..Otherwise, this thing is a boat anchor. : )

Krell is recommending capacitively coupling the amp to resolve the glare issue-FPB is direct coupled of course. Something they recommend to do with Tube Preamps regardless, which I have. The KAV I owned before this FPB comes from the factory capacitively coupled. I personally think this is not the answer in trying to resolve sibilance, but the only thing that is compelling me to do it is the fact my KAV sounded great. Alot sweeter. If adding a capacitor into the signal path will change sibilance I will do it, but given the fact there already about 500 Caps already in the path, I have my doubts that adding one more will do much in softening glare.

Working in steps, taking deep breaths trying to be patient as I go..Otherwise, this thing is a boat anchor. : )

Funny for Krell to recommend capacitive coupling! Did they say whether it is input or output coupling you need? I assume input since you mention your tube preamp (and yes, this is a good idea) but I have read some speaker designers say that lack of output amplifier coupling is the reason for glare - and not input coupling. I am not sure which is right but I would place my bet on output coupling, especially with B&W impedance curves. Output coupling can also be done with a capacitor but it is best to use a transformer (like tube amps and McIntosh amps). The transformer also allows for impedance decoupling which is a much more elegant solution that adding a simple cap (although it costs a lot more).

In many direct-coupled amps, the DC often gets shunted in the voltage gain stage anyway. The input coupling cap just makes sure that the input differential current mirrors are have proper midpoint bias. Adding a cap at the input can really distort the waveforms if the circuit isn't designed for it at the outset due to nonlinear frequency gain. This is also why I think output coupling might be what they were referring to. Hard to say which is best without a schematic of the amp however.

Also, you mention having 500 caps in the signal path. This is incorrect. The caps you see and think of are actually in parallel to the path and/or in the bias loop and not signal loop. The cap Krell is talking about is actually in SERIES with the signal path, whether input or output. Huge difference.

Arthur

Jc51373, the Pass X250.5 was an excellent addition to my system. It is truly a world class amp. Resolving, dynamic and smooth. Really can't find any faults or anything I would like to improve on as far as amplification.

I am pretty surprised that you have to do some kind of mods to this amp to make it work with your preamp. Hmmmm

I think that the sibilance could be in part due to your interconnects and speaker cables. Do you experience this sibilance on all the recordings or just some?