Krell FPB 700 CX DC Jumper

[Ossidian]

Krell FPB 700 CX wanting to use tube preamp. Jumpers are advised with caps being engaged due to "potential" DC. Based on the pics attached, the jumper above labeled JMP1 for tube preamps? Purchased used and Krell is under restructuring. Any help appreciated. Thank You.

 

[Alrainbow]

The blue boards are the last revision so real cx.
have you looked online or downloaded a user manual ?

 

[godofwealth]

I used a Krell 700CX for many years with an Audio Research Reference 1 preamplifier with no jumpers installed. You might hear a small pop through the loudspeakers when you mute the preamplifier. No good tube preamplifier generates much DC to be concerned about, as long as you stick to reputable brands. Of course, I can’t guarantee your outcome based on my experience, but it sounds to me like this Krell advisory is out of sheer precaution. I wager many WBF folks use a tube preamp with a solid state amplifier. It’s a popular combo, and I don’t think it’s any cause for concern.

 

[Paul1960]

I researched this when I got my Krell 650Ms and discovered that there was general agreement that you didn't need to make that change for Audio Research preamps (I use a Ref 5SE) and most believed that there was just one brand of preamp that had posed problems but I don't remember what it was. I think you can safely ignore this but I would try it with the volume quite low the first few times.

 

[microstrip]

I researched this when I got my Krell 650Ms and discovered that there was general agreement that you didn't need to make that change for Audio Research preamps (I use a Ref 5SE) and most believed that there was just one brand of preamp that had posed problems but I don't remember what it was. I think you can safely ignore this but I would try it with the volume quite low the first few times.

Yes, this Krell advice was for some tube preamplfiers with leaky output capacitors - usually oil filled types that could have significant DC at the output and generate nasty DC clicks or put the amplifier in protection mode. As always, measuring the preamplfier output DC with a voltmeter is the best way to know. Never has problems with ARC, VTL or conrad johnson preamplifier with the FPB600 or FPB750mcx.