Hum from headphones

Nino75

New Member
Hi forum members,

I have a problem with the jamo avr 793, 7.1 receiver. When I connect my headphones I can hear the bzzzz sound at the one side. The bzzing is heard even when there is the sound volume is at the minimum. Increasing the volume doesn’t affect the level of the bzzz noise. I tried to clean the connections but it´s still the same.

The big toroidal transformer is just next to headphones jack.

So do you have any idea what that could be.
:scratch2:
 
Couple of things, try another set of headphones to rule those out. Is the buzz consistant in all modes i/e tuner, aux, etc?
 
I tried the other headphones and nothing.
The bziing is heard no mater what input is being used cd, dvd, tuner.
 
Without a schematic it will be rather difficult to troubleshoot. The unit appears to be newer and rather expensive. Is it still under warentee? Either way, some systems use a simple voltage divider of sorts taken from the audio out for headophone use. I have also seen a discrete headphone circuit used in some Japanese units (Sony). Sounds like you have a bad ground somewhere in the circuit. If you are not worried about warentee, then follow the wiring back from the jack and see what type of components you see. Is there a small board at the jack? a couple of resistors? take some pics as well.

Rogers
 
Thanks a lot Roggom,

I bought it four years ago, but I was in France and I was not using it. The warranty has expired two years ago.

Also the jack is situated on small board and it's a small unit, but you can see on the photos. I'll tried to put teflon tape around it and to move it away from transformer but the buzzing is still there. So, I disconnected the wire that supplies a signal and power to headphones jack, and now I started to dismantle unit and will try to use teflon tape and alu tape to isolate possible leaks from wires or EMI from transformer.

I don't know if it will do any good, but I'll try to see what happens.

Also I'll try to improve the cooling.

So,If you have any other good ides just write.

Hope i CAN PUT IT BACK AGAIN :scratch2:

Thanks again
 

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Buzz could be in main amp. section.

The buzz could be in the main amp. section, try and hook up 2 small speakers you can get your ear next to and listen with the volume all the way down, if the room is quiet you may hear the buzz in one speaker.

If the main amp. seems "clean", then several possibilities exist, what you are calling a buzz may be a low pitched HUM, and the speakers are not reproducing it, the headphones are.

Try putting wires onto a "loose" headphone jack and connecting it to where the speakers go and see if you have hum\buzz then from the phones.:scratch2:

*CAUTION!* Make sure the volume is all the way down and then put the phones on your ears, don't play music, you are only listening for buzz\hum as the phones (and your ears) are NOT protected by resistors from the main speaker outputs on the amplifier.:no:

The headphone jack has its own tiny amplifier and has a bad ground or hum pickup in ONLY its circuits.

The above methods are used to isolate the location of the buzz, MAIN amp. or HEADPHONE amp. (if equipped).

Mark T.:music:
 
Hi Mark,

Yes maybe I didn't recognize it well buzz from hum, but definitely the speakers are not reproducing it, maybe it's low pitched HUM. When I'm connecting headphones, and I start to insert the plug, first this buzzing is heard on the left channel, and when I push the plug till end the buzzing on the left is stopped and it's transfered on the right.

Untill now I did some rechecking and some smaller mods.

First I changed the power with the shielded one, connected the shield to the ground on the wall side.
After, I removed the fan that was inside on the heat sink. Fan was starting to work when the temperature gets hi and the noise was irritating, so I'll use one or two external for lowering the heat, and I'll try to find maybe other way of reducing the temperature.

No result.

After this I removed the big toroidal transformer to see if everything is OK with him. No visual problems. Put some anti-vibrating material like blue tack under it.

Next removed the board where 4 big caps ( 4 jamicon 15000 uf), two smaller transformers, ac input, 4 big elnas, and everything looks ok, nicely soldered no visual problems.

After I tried to put some Teflon tape around some of cables that are inside ( because the number and the way that these cables are put in chassis is more than chaotic). Also near torodial transformer, I put some aluminum tape, I tried to crate some kind of barrier towards nearby cables that are passing near.

But, the buzzing still was there.

After this, I disconnected the cable that supplies the headphones part and four led lights on the front of the receiver. This cable goes from the back of the chassis were is preamp, dac etc. towards the front of the receiver.

I must say that, after turning off headphone input, the sound is slightly improved, more detailed.

I'll try to recheck the amp board near the heat sink, and pramp/dac board and see if there could be some problem.

Thanks all, and write all ideas you have:scratch2:
 
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