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tube pre amp and Krell FPB 600

Krell in its reference manual says : Tube pre amplifiers , by design, are capacitively coupled. For this reason, the benefit of a direct coupled amplifier can not be realized when used with a tube preamplifier. Additionally , many tube preamplifiers output a great deal of DC. This DC may exceed the servo of a FPB amplifier. Excessive DC level in a signal can damage amplifier , speakers , or both.
Can I use Air tight ATC 2 pre amp with Krell FPB 600 ?
Please advise.
Thanks
fpooyandeh
carz
8 posts
 
Have anyone have any experience upgrading the Krell input coupling caps ? Can you share your experience ?
atmasphere's avatar
atmasphere
11,656 posts
 
The input of the Krell is direct-coupled (no coupling caps). This is why they are 'concerned'. However, the claim that tube preamps put out DC is ridiculous. They no more do that than solid state.
salectric
747 posts
 
With due respect to Ralph, I think Krell's concern about tube preamps being used with their direct-coupled amps is a valid one. Many tube preamps have a substantial low-frequency pulse on turn-on and turn-off which can cause major problems for a high-powered direct-coupled solid state amp. Note that these pulses occur notwithstanding a coupling capacitor on the output of the preamp. Most modern tube preamps have a muting relay which allows the preamp voltages to stabilize before the amp is connected. However, not all tube preamps have muting relays and Krell is understandably going to err on the side of caution. No manufacturer wants an unhappy customer.

Of course, Krell could have just warned that the power amp should always be turned on after the preamp has warmed up and turned off before the preamp. This simple procedure would also solve the thump problem, but then who wants to count on their customers actually following this advice.
audiolabyrinth's avatar
audiolabyrinth
4,555 posts
 
Of course, Krell could have just warned that the power amp should always be turned on after the preamp has warmed up and turned off before the preamp. This simple procedure would also solve the thump problem, but then who wants to count on their customers actually following this advice.
This is a bit of info I can certainly use for my Krell 700cx, thankyou Salectric.
ct0517's avatar
ct0517
2,041 posts
 
Of course, Krell could have just warned that the power amp should always be turned on after the preamp has warmed up and turned off before the preamp. This simple procedure would also solve the thump problem, but then who wants to count on their customers actually following this advice.

Salectric / Audiolabyrinth

Krell makes a really big deal about this in my Krell manual. In fact it takes up a whole page. Its hard to miss. This process / procedure of amp/s turned on last and first off is an Audiophile 101 rule. For the last 30 -35 years with me anyway.

Audiolabyrinth - see page 15 Amplifier Operation section of your manual.

Cheers
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