My daughters amplifier is having issues at the moment..When headphones are plugged into this Amp..the headphone relay does not kick in...and sound comes out of both headphones and speakers at the same time! I have the circuit (see attachment) was wondering could anyone help me understand the logic from this circuit diagram of how exactly plugging in the headphones makes the relay energise...Im struggling to follow the diagram..... Looking at it the 'headphone' relays contacts are normally closed... any help most appreciated in helping me understand further. I must add the amp has had problems recently where one channel starts to crackle...Ive found a couple of dry joints..and currently its under test to see if it comes back...not 100% that is cured at this stage....it seems these issues can be a combo of things and Im not counting my chickens just yet ..! The speaker relays (one each for A and B speakers) seem to work fine...Ive cleaned their contacts with some deoxit...however the 'headphone relay' is of a different type and appears sealed. Any help given is most appreciated. Cheers
Attachments
The diagram is a bit to small to look at detail but at first glance I can not see any auxiliary contacts on the h/phone socket that could be used for sensing when a plug is inserted. It is drawn as a conventional socket with three terminals.
Are you sure it should operate automatically ? or does it rely on the user turning the speakers off via the front switch ?
Are you sure it should operate automatically ? or does it rely on the user turning the speakers off via the front switch ?
I would guess the relay is used for normal muting and for switch on delay protection to avoid thumps and so on. And DC offset protection as well of course.
The headphone output has to be treated as if it were speaker as far as the listener is concerned with no untoward noises and so on being allowed to get through.
The headphone output has to be treated as if it were speaker as far as the listener is concerned with no untoward noises and so on being allowed to get through.
Actually ..I think you are right with where you were going! the relay must be simply protection for the headphone on startup...just proved it IS kicking in by turning to OFF speaker selection switch then pressing Standby to turn off amp....then listening to headphone and relay pressing standby to turn amp back on....no sound from headphones until 'click' from what has to be the head phone relay!...case I think solved! Cheers 
that's good. Those are the faults we like 
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