I OWN A NAD M 25 ---7 CHANNEL AMPLIFIER. I AM USING 4 CHANNELS TO BIAMP MY SPEAKERS. ONE OF THE UNUSED CHANNEL IS SHOWING A RED PROTECTION LIGHT.THE BIAMPED CHANNELS ALL WORK FINE ...I HAVE CHECKED ALL CONNECTIONS....NO CONNECTIONS ON THE CHANNEL SHOWING RED PROTECTION LIGHT. CAN I CONTINUE USING THE AMPLIFIER.

https://elektrotanya.com/nad_c370_sm.pdf/download.html

https://music-electronics-forum.com/forum/amplification/other-amps/920148-nad-c-370-no-sound-from-speaker-outputs#post920172

https://audiokarma.org/forums/index.php?threads/nad-c370-repair.916194/

What is the speaker load in Ohms that you are running? Or what exactly is hooked up to it? are you bridging it? The protection light will come on if the load is too much for the amp to handel. If the load (in Ohms) is less than the rated load that it can run, it will stop the output to keep the amp from self destructing. The amp will sense that the demand for power will be too high for the amps circuitry which will either make the amp get so hot that it will burn up the copper on the board or more likely burn up the power mosfetts that power the speakers. If the Ohms are within range then it will allow power to flow through the circuit until the rails that the mosfetts are bound to until they get so hot that it will go into thermal protection. So if your amp has both thermal and overload protection lights and the overload is light then the load is probably too much for the amp. if it's bridged in mono the you can only have 1 speaker setup hooked up it if it's a 2 channel amp. a 4 channel amp bridged in mono for both front and rear channels will be able to have 2 speakers rated a 4 ohms each hooked up to the amp 1 set per bridged output or channel.
Try it running in stereo with only 1 speaker per channel and see if it will produce sound. If not then you have an amp that has internal problems and will need to be serviced. Check your warranty to see if you are covered.

There are four posts - two black and two red. They should be connected together, as shown in the picture. If you are missing the brass straps, simply use wire to reconnect the posts, black-black and red-red.

Then it's a simple matter of connecting the red (+) amplifier output to one of the red terminals, and the black (-) amplifier terminal to the black terminal on the KEF.

The KEF terminals can be seperated if you wish to "biamp" or "biwire" these speakers. Each black/red pair is dedicated to either the bass or the treble. For higher fidelity, some listeners prefer to run seperate wires from a single amplifier channel to each individual speaker input.

See link below.

http://www.pithed.org/2007/10/12/nad-c370-protection-circuit-repair-amp-fails-goes-into-protection-mode/

the amp is going into protect mode due to something wrong in the amp or some thing in the wiring to it ooh yea if you are getting 18v power to the amp that is way to high it should not be higher then 15v if the amp is in protect mode it will not play at all.

It probably has shorted output transistors. To eliminate other possible causes, read through the following page.

Amplifier in Protect Mode - Troubleshooting

Let me know if you have any other questions.

Sounds like you have lost the power amp transistor(s) or IC for this channel.

If you have a 4 channel amp and 4 speakers and each speaker is connected to each of the 4 channels you are just fine.
A stereo amplifier has 2 channels, typically labeled left and right and each channel has an amplifier. A 4 channel amplifier has 4 amplifiers. With one speaker on each channel, there is one speaker on each amplifier. Audio amps are referred to as amps or amplifiers, although if they have more than one channel it would be more correct to call them something like 'multi-channel amplifier' or 'multi amplifier speaker driver'. Semantics.

you probably have the speakers set to where it ecxeeds the ohm load limits. its only 4 ohm stable when bridged and two ohm stable when ran using two channels. so either run the speakers at 8 ohms each parallel or just hook one speaker to eack channel. if you do not know what i am talking about then just email me at [email protected] and give me the speaker specifications.

I suggest rechecking the speaker wiring in case there is a small "whisker" of wire touching either the case or adjacent terminal, also check the speaker end of the wires for same. Do you have a pet? I have seen wires chewed partly through by cats (& rabbits)! See the information from the manual below: http://207.228.230.231/manual/NAD-C370.pdf