Help My Krell 700cx isn't working right.

From whom did you buy it? Have you contacted him/her/them? Have you contacted Krell to ask them what they think? Do you have another amp to plug into the system to see if the problem remains? Have you tried a post on the Audio Asylum?

Caveat, I don't know much of anything about the Krell stuff's operating parameters, but it sound to me like the amp is detecting too much DC output from the pre-amp and is shutting itself down. FWIW if it helps get you pointed in the right direction.

Agree with Newbee - try a different preamp (I have a Krell FPB-600C).

You didn't mention the preamp that your using.

I back tracked and saw the person you purchased the 700cx from and he also had a KCT for sale at the same time is that the preamp your using with it.

There is a capaictor on the input that you might need to connected to block dc from the preamp. There should be two small connectors/jumpers on the circuit board near the inputs. Removing the jumpers will put the capacitors in the circuit.

Are you using a tube preamp?

Below is the web address for the FPB-700cx:

http://www.krellonline.com/archive_pdfs/FPB_STEREO/0162_020_MAN.pdf

Here are some relevant excerpts:

POSSIBLE CAUSES
Excessive DC at the
amplifier input

Electrical short in speaker
cables or inside speaker
Insufficient AC current from
the wall outlet

Excessive heat

DC present at the output
stage

Internal amplifier problem

COURSE OF ACTION
If preamplifier is a tube
model, see Using a Tube
Preamplifier, on page 14.

Check all speaker cables for
any cuts or frayed edges that
might form a connection
between the positive and negative
speaker binding post terminals

Make sure the AC line is at
least 15 amps for 300cx and
350Mc amplifiers; 400cx,
450Mcx, 700cx, and 750Mcx
amplifiers should be
operated from a dedicated
20-amp line.

Allow amplifier to cool before
resuming operation. See
Placement, on page 4 for ventilation
requirements

USING A TUBE PREAMPLIFIER
The high DC output of tube preamplifiers may
exceed the DC protection circuitry of Full
Power Balanced amplifiers. Excessive DC
level in a signal can damage amplifiers, speakers,
or both. The coupling capacitors in Full
Power Balanced amplifiers must be engaged
when using a tube preamplifier. An authorized
Krell dealer, distributor, or Krell must activate
these capacitors.
Coupling capacitors must be inserted into the
signal path by your authorized Krell dealer, distributor,
or Krell before you can use your Full
Power Balanced amplifier with a tube preamplifier

Thanks every,first,I used the tube pre-amp, then tried the solid state, and used the ISO-Max for RCA tranfer to balance, I measured the voltage for 30 minutes using the voltimeter, and the voltage was V115-V119. most time at 117-118, When I'm playing music, the amp went to standby at different time (some time only in one minute) but the voltage was at normal,