tube pre amp and Krell FPB 600

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.

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.

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

Salectric, Historically tube preamps have been in use with solid state amps for **decades**! Solid state amps by their very nature have to have a protection circuit, and there aren't any warmup thumps that a tube preamp can make that can damage the input of a transistor amp. The protection relay is there to protect the speaker, not the amp.

Ever tried turning on a solid state preamp after the amp is already on? They thump too!

Singling out a tube preamp when solid state preamps are just as guilty is ludicrous. Ct0517 got it right- **no matter what kind of preamp you have**, it gets turned on and stabilized first before you power up the amps.

I think you will find that all preamp manuals state something to this effect unless the preamp has a warmup mute feature.

That statement in their manuals is misinformation in a very pure and refined form.

I agree that it is not likely a preamp turn-on or turn-off thump will damage the power amp. The real point is the damage to the speakers. Krell has good reason to be concerned about this in my opinion.

Since I have been all-tubes for many years, including phono, linestage, power amps and even DAC, I really don't have a dog in this hunt. Whatever Krell does or does not do is of no concern to me.

I would never underestimate, however, the ability of some well-meaning audiophiles to mess things up. I clearly recall a lengthy exchange I had on some forum, probably Audiogon but I am not certain, where the other party was insistent that a preamp should always be turned on after the power amp, never before. (That is not a typo.) He dismissed my concerns about possible damage by saying he had never had a problem or experienced any thump for 20 or more years. Of course, his good experience hardly proves the rule; it just shows the muting relay in his preamp works.