Marantz P400 cuts out at low volume

Speaker relay contacts. They might be cleanable or the relay(s) can be replaced.

Mark Z.

This can be from the protection relay being defective, or from some components in the output stage, and or driver stages, and or the power supply section, that have gone slightly off value from age and use.

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JANA _____

one and sometimes both channels fuz and cut out itermitantly. It seems to be worse at low volume settings and will usually cut in during peaks such as kick drum beats or when the vocals start. my best bet is perhaps a capacitor in the power amp stage has failed but which one?

i have checked for dry joints as best i can and there also does not seem to be any speaker protection relays that may be playing up.

any help?

Try playing it at a higher level and tap on the chassis. If you hear a breakup corresponding with your tapping then that would suggest a mechanical coupling problem in the signal path. If the 400 has mechanical switching of the inputs or modes maybe those switches need a shot of contact cleaner. You said the 400 has no relay for speaker protect so that can be ruled out of course :) Good luck.

Most Marantz amps of the era did use protection relays - often they had opaque grey or black covers, so they may not be immediately obvious when looking into the case. It does sound like a classic relay problem. DON'T put any kind of cleaner or liquid into a relay, you'll wreck it. Same goes for sandpaper. Just slip a piece of uncoated writing paper between the contacts and jiggle it up and down to dislodge any dirt. Sometimes arcing wrecks the contact plating and you have to get a new relay.

Of course standard procedure in rehabilitating a 20 year old amp is to put a shot of DeOxIt into every pot and switch, and work them a couple of dozen times each.

Do make sure you check the DC voltage at the speaker terminals before hooking up any decent speakers - anything above 50mV indicates that the offset needs to be adjusted, otherwise you end up passing a steady current through your speakers which can make them liable to burn out their voice coils. If you see an initial large voltage which drops away fairly quickly, the outputs are capacitively coupled and you're OK.

Cheers, MK.

Cheers guys. Just wondering where the protection relays would be positioned if they were there?

Thanks

If there is a preferred location it would be near the audio amp.