Quad 33 hum

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24-Jul-2017 11:39 PM

hummph

hummph

Posts: 29

I have just completed a dada spec  revision to a Quad 33 and it now sounds great. However, there is a slight hum on both channels when any of the filter buttons are selected, this increases slightly when the bass is turned up. When the cancel button is selected the hum disappears. Any ideas where I should be looking?

Also, if the balance control is removed can it be replaced with two 500r resistors? ( One from c5 to gnd and the other from c6 to gnd?

Thanks

Ken

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25-Jul-2017 09:51 AM

Joost Plugge

Joost Plugge

Posts: 920

The hum is picked up by the filter inductors, so there must be a hum source nearby, like a tuner or other device. Check if the hum is still there when you switch off nearby equipment. Your balnce control mod is ok.

Joost Plugge

DaDa Engineering

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25-Jul-2017 11:44 AM

QuadOAP

QuadOAP

Posts: 9


This solution may be a bit too simple.

I had a similar hum problem when I did the upgrade a couple of years ago. I was operating the 33 with the cabinet removed for test purposes. This defeats the screening. The hum disappeared when I fitted the cabinet. It is something to do with induction in the coils in the filters. They are not in circuit when the cancel button is pressed.

I learned something that day. Faults are not always complicated.

OAP

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26-Jul-2017 06:55 PM

hummph

hummph

Posts: 29

Thank you for your replies.

I will investigate further this weekend. The pre-amp is well away from other sources of interference and, yes, I have also learnt to keep the casing on!

I have another good revised 33 which I use regularly so I'll swap the boards to see if that makes a difference.

Regards

Ken

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