Message to G4VSQ

[DvnDave]

Hi, I know this is a Merc forum and Ive had lots of help on my car probs but I also have probs with my Quad 303 power amp and can't find any assistance on Quad forums, noticed you said you are a radio engineer and wondered if you can help or point me in the right direction for sites that might be able to help.

On switch-on there is a very loud thump from the kef speakers so loud I'm afraid that the cones are going to leave their frames! Iv'e checked the very large output capacitors using an Avo model eight and they seem to charge and discharge ok. Apart from switch-on the amp runs as usual .. superb. So, long shot I know but despite posting probs on various Quad sites only one reply and that didn't help.

Many thanks in advance,


DvnDave

 

[alec]

303

Hi I am not the man you wanted but recognise the question.

This was a problem with many eary solid stste amps. Have yours always done this?

I cannot remember the circuit , if you have it e mail me a copy and I will see if I can make a few suggestions.

Could be the output capacitors.
Put a dc voltmeter across the speakers it should read zero when running normally.

Alec

 

[DvnDave]

Quad 303

Hi Alec, thank you for taking the trouble to reply.

In answer to your questions, until very recently on switch-on there was always a distinctive thump but nowhere near as bad as now.
I don't have a hard copy of the diag but there is one on line via research triangle laboratories - geocities.com/researchtriangle/lab/6722/quad303 (phew) I don't know enough about these computer thingies to forward the copy I have saved on my disc also how do I find your email?

Thanks once again for your help,

Cheers from a wet and windy south devon.

 

[alec]

303

Are you safe working on electrical items? be carefull as mains voltages are around.

Have had a look at the circuit on the web and it is not unusual in any way.
There does not seem yo be any special protection against thumps.

But if they have got worse then somthing has changed.

Dissconnect the speakers, put a dc voltmeter set on say a 25 volt range across the output terminals, switch on and after about 10 secs the reading should be zero.

If not suspect the output capacitors.

If the previous test was ok then reconnect the speakers.
Then disconnect the pre amp and turn on the 303, is the thump still there? If not then the pre amp may be to blame. (this test may not be possible in your set up)

Other wise it could be anything .

Probably a capacitor, possibly the main resevoir.

Alec