Noise from a Quad 405

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19-Dec-2019 11:02 PM

Yoplaboum

Yoplaboum

Posts: 3

Hello,

I get noise at the output of my 405 (last board, rev. 9 or 10). In this amp, the 2 power caps were changed, with the 3 electrolytics on each board, and C15 and C16.

My amp begun to produce a noise, I don't know the english term for that. It's like the noise of the wind on a microphon. It's not loud, and the volume of the noise remains the same, whatever the volume on the preamp. This sound is more present on one channel (right)

This noise is more frequent, nearly continuous, when no music plays, and it seems to stop when the amp plays to a significant level for a long time.

Perhaps someone got the same problem with his amp ? A last question : There are electrolytics on the speaker terminal board, I didn't change them, it's not easy to do. You you think these capacitors on this board can be the cause of my problem ?

Thank you very much, and merry Christmas !! :-)

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20-Dec-2019 11:38 AM

Stefaan

Stefaan

Posts: 628


Is the noise there when the inputs of the 405 are disconnected from the preamplifier?

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20-Dec-2019 09:22 PM

Yoplaboum

Yoplaboum

Posts: 3

I am ashamed... The cable was the problem.

I disconnected the preamp first (a Nad C160), the noise wasstill there, then I unplugged the amplifier, and no more sound. I tried with a old and chip cable, a thin and common one, and it was ok. So sorry for the disturbance.

Nice WE to everybody ! :)

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21-Dec-2019 11:49 PM

Yoplaboum

Yoplaboum

Posts: 3

No, in fact the noise has not diseappared. It's lighter, but present again on the right channel. Sometime, not always. It's like a blow, more or less present, and sometime this blow grows, until a small "pop", then the amp is quiet, until this noise comes again. For me, it's a sick capacitor, but I'm not sure... I will check again all the joints on the boards, and change all the silver capacitors. If someone has an idea about it, he's welcome !

Have a nice Sunday ! :-)

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23-Dec-2019 02:22 AM

EJP

EJP

Posts: 1690

Sounds like a noisy transistor to me. Try replacing Tr2.

EJP

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