tube pre amp and Krell FPB 600

12-04-14: Audiolabyrinth
I always get a thump sound over the speakers when I turn my amp off, it's really alot of power, seems normal to me.

Hi Audiolabyrinth
As explained by Krell to me it’s a small amount of DC that escapes through the outputs as the relays shut down. Not hazardous to speakers.

My Krell amp makes a very subtle thump at shutdown only too. My previous OTL monoblocks would do it at startup and shutdown. The Classe amps were both startup and shutdown but only occasionally. The others I owned like multiple Bryston amps, and others I demo'ed like Pass Labs and others I can't remember. My Roger Modjeski Rm9 and Rm10 tube amps do not do it.

Cheers

Roger Modjeski RM9 and RM 10 tube amps?, mmmm can you tell me more about them?, I have never heard of this!, are they U.S.A. branded, what's the story?

12-04-14: Audiolabyrinth
I always get a thump sound over the speakers when I turn my amp off, it's really alot of power, seems normal to me.

I've always turn my amps off before pre and don't get a thump even with a Krell FPB600.

Hi Knghifi, yes, I am going to do the power up and power down that salectric has specified in the above post, interesting, you said that by doing this, I may not get that turn off thump with My krell 700cx that will be back from krell today with up-graded power supplies and along with complete new and improved caps that they installed earlier this year that was not the stock caps that was in the amp when manufactured,I am going to do what you and all have said about power up and down scheme, Thankyou Knghifi.

12-04-14: Audiolabyrinth
Roger Modjeski RM9 and RM 10 tube amps?, mmmm can you tell me more about them?, I have never heard of this!, are they U.S.A. branded, what's the story?

Hi Audiolabyrinth

Here is Rogers' US website. branded as Music Reference

I discuss the rm9 and rm10 in my virtual page. Feel free to stop by and say Hi.

Knghifi, A.L., et al

Re; the amp shutdown noise we have been discussing. here is some more info on it from Krell that sheds more light.

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The noise you are experiencing is not a problem with the unit nor is it a byproduct of your AC mains (*). This is normal for large powerful amplifiers that are not “capacitor coupled” (AKA: no capacitors in the signal path or at their outputs).

*Were your line AC to consistently run low (at or below 100v) this could “possibly” (not definitively) cause the power supply to fall slightly out of regulation, which could possibly (again - not definitively) exacerbate this noise upward slightly.

Also, if the amplifiers are turned completely off (including the rear panel breaker) between listening sessions, this will cause the noise to be louder. Leaving the units in standby allows part of the power supply to stay warmed up, thus reducing this noise. That said, should one wish to not leave them in standby due to their power consumption, this noise should never be loud enough to damage the speakers upon turn on or off.

Regards, Patrick

Patrick Bresnahan
Sales, Technical Support, Service

Krell Industries LLC

45 Connair Road, Orange, CT 06477 - USA