MC402 vs FPB 300cx

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?

Thanks Aball...Some good points you made. I am going to lift the hood on the amp today and remove the jumpers (per instructions from Krell) on the input stage of the amp itself.VTL is capacitively coupled on the output, so it is now double CC'd.

I will be impressed if it changes anything, expectations are low. Based on some of the points you made though and the fact my KAV was coupled on the input stage it makes sense to eliminate this as a possible solution to the glare.

The MC402 I had did this exact same thing, glared.

If you are hearing glare from two nice and very different amps, then the problem may not be the amplifiers at all. I think I would start looking for problems elsewhere in the chain...

Arthur

Good point, but it only happened/happened when they were inserted into the system.