Well! My experience is different.
What happened is that when I connected my BAT Vk-3iX preamplifier to Krell FPB 300 without knowing about the coupling capacitors engagement, the combo performed wonderfully. However, one day there was a loud popping sound from both speakers and right channel went mute. I reset everything but now Krell FPB 300s right channel had intermittent operation, it will work sometime but not the other times. I sent Vk-3iX to BAT and FPB 300 to Krell. BAT gave the ok signal that Vk-3iX was performing as per specifications but Krell told me that right channel of FPB 300 had intermittent short in the driver board and reason seems to be from high DC at input of FPB 300. Krell changed the board and a controlling processor but engaged the coupling capacitors in FPB 300. BAT Vk-3iX is from new line of BAT but I measured max of 11.3 mV DC at it output. BAT says up to 14 mV DC is normal for it. However, Krell says that it is not average level of DC that hurts direct coupled amplifiers as DC servo in amplifiers can and do counter it but it is the extremely fast spurts of DC as high as 100-200 mV DC from tube preamplifiers that does the damage. I measured max spurt of 56.67 mV DC at VK-3iX output. However, BAT says if max function in digital multi-meter is used then it can measure low frequency AC magnitude which can depend on line supply quality I can continue writing about this for one more page.
I sold FPB 300 to experiment with Parasound JC 1s but I hated JC 1s sound. Whatever the Stereophile writes in favor of JC 1s, they are not even close to Krells FPB series. Now I have been using BAT with FPB 400cx with coupling capacitor engaged in Krell for six month and so far everything is fine.
But this is not an isolated problem with Krell only. All amplifiers which does not have coupling capacitors as protection against DC and only rely on servo to counter DC face the similar risk. I once read somewhere about a Parasound JC 1 that got fried when the owner turned off the preamplifier before turning off the amplifier. Some preamplifier (even solid state) spurts DC when they are cycled on/off and this alone can fry an amplifier which doesnt have coupling capacitors as protection when its servo failed to counter high level of DC. JC 1 doesnt have coupling capacitors thus in above case it got fried.
What happened is that when I connected my BAT Vk-3iX preamplifier to Krell FPB 300 without knowing about the coupling capacitors engagement, the combo performed wonderfully. However, one day there was a loud popping sound from both speakers and right channel went mute. I reset everything but now Krell FPB 300s right channel had intermittent operation, it will work sometime but not the other times. I sent Vk-3iX to BAT and FPB 300 to Krell. BAT gave the ok signal that Vk-3iX was performing as per specifications but Krell told me that right channel of FPB 300 had intermittent short in the driver board and reason seems to be from high DC at input of FPB 300. Krell changed the board and a controlling processor but engaged the coupling capacitors in FPB 300. BAT Vk-3iX is from new line of BAT but I measured max of 11.3 mV DC at it output. BAT says up to 14 mV DC is normal for it. However, Krell says that it is not average level of DC that hurts direct coupled amplifiers as DC servo in amplifiers can and do counter it but it is the extremely fast spurts of DC as high as 100-200 mV DC from tube preamplifiers that does the damage. I measured max spurt of 56.67 mV DC at VK-3iX output. However, BAT says if max function in digital multi-meter is used then it can measure low frequency AC magnitude which can depend on line supply quality I can continue writing about this for one more page.
I sold FPB 300 to experiment with Parasound JC 1s but I hated JC 1s sound. Whatever the Stereophile writes in favor of JC 1s, they are not even close to Krells FPB series. Now I have been using BAT with FPB 400cx with coupling capacitor engaged in Krell for six month and so far everything is fine.
But this is not an isolated problem with Krell only. All amplifiers which does not have coupling capacitors as protection against DC and only rely on servo to counter DC face the similar risk. I once read somewhere about a Parasound JC 1 that got fried when the owner turned off the preamplifier before turning off the amplifier. Some preamplifier (even solid state) spurts DC when they are cycled on/off and this alone can fry an amplifier which doesnt have coupling capacitors as protection when its servo failed to counter high level of DC. JC 1 doesnt have coupling capacitors thus in above case it got fried.