Revisioned Quad 303 startup hum after working fine

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18-Apr-2017 04:17 PM

Frank

Frank

Posts: 31

I have had my Quad 303 revisioned with the Dada kit and it has been working fine for some months. Now all of a sudden there is a hum on power-on from both channels for two or three seconds. It is not the pre-amp as I disconnected it and the problem still occurs. 

What can cause this and is it dangerous for the amp itself. If I would add the Velleman K4700 kit and add a delay I think I can get rid of it but I have to be sure that in the long run it will not damage my Q303.

Thanks

Frank


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18-Apr-2017 06:15 PM

quadany

quadany

Posts: 21

Hi Frank,

Have you seen "303 buzz/hum on power up" by Ray (31 march - 6 april 2017) ?

(I cannot paste a link in this forum)
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02-May-2017 01:25 PM

Frank

Frank

Posts: 31

Hello,

I did see the post but this seems unrelated. In that case there had been adjustments to the PSU that lead to the fact that there was a hum for a couple of seconds on the left channel and after that no sound from the left channel.

In my amp the hum/buzz is from both channels for 2 or 3 seconds and then the music is playing from both channels.

Any hints are welcome!

Frank

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02-May-2017 03:02 PM

quadany

quadany

Posts: 21

Hi Frank,

Do we have read the same post? In Ray's post "303 buzz/hum on power on" Ray writes:
(a pity that I can do no pasting in the forum...)
"The problem I now have is that on power up there is a fairly loud buzz/hum on the speakers. It lasts about 1.5 seconds and fades quickly. After the initial noise the amp seems to perform as it should and sounds fine".

Both speakers, 1.5 seconds, works fine after that.

Seems very close to your description...
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03-May-2017 06:00 AM

EJP

EJP

Posts: 1412

It sounds exactly the same to me.
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03-May-2017 09:56 AM

Frank

Frank

Posts: 31

Sorry I totally agree with you both. I was refering to a different post. 

Can you tell me if the transistor we are talking about is TR201?

Frank

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03-May-2017 01:01 PM

EJP

EJP

Posts: 1412

It is Tr3.
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02-Oct-2017 10:32 AM

Frank

Frank

Posts: 31

Wow. The problem is solved and indeed it was a contact of one of the pins of the power transistors to the heatsink. I bent the pins such that they no longer touch the heatsink and the hum is gone.

Thanks all for the valuable help!

Frank

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