Quad 303 and 34 - Hum/buzz sound

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21-Jun-2018 12:46 AM

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Posts: 1

Hi there,

I recently purchased a Quad 303 that goes in 34.

Upon listening to them before buying, I did not notice any unusual sounds. However, after installing them in my apartment, there is a distinct "wind noise/hum" on both speakers, and a slight buzzy/parasite sound on the right speaker.

I believe it is coming from the amp, as the sound is noticeable when only the amp is on. It is not linked to the volume on the preamp.

After reading a bit on the subject, I think it could be a ground loop. 

For info, all the system is plugged on one extension cord, which is one outlet. 
The 303 has been serviced and a power switch has been added to it. Most of the parts were switched and upgraded 10 years ago.

I ran a few tests and unplugged all the things from the outlet (turntable, tuner, preamp, TV, raspberry pi, PS4...), the buzz/hum is still here. However, if I change the outlet in which the amp is plugged - no extension cord in this case -, the sound gets louder. 

I might be wrong here, but if I read correctly, the preamp should be grounded, but the amp should not be. I don't have the cable that was linking the preamp to the amp for power (or is it the 4-pin DIN cable? Not sure about this).

I was wondering if there were any tests or if someone had any ideas about this issue?

Thanks a lot in advance for the help. I'm a happy new Quad owner and I have always been impressed by them in the past. Hopefully this is a minor issue and I'll be able to enjoy these two great pieces of electronics fully soon.

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12-Jul-2018 02:33 AM

EJP

EJP

Posts: 1511

The preamp should be grounded; the amplifier is powered from the preamp via a non-grounded 2-core mains interconnect cable; and it is grounded via the signal lead. The mains interconnect is 2 core, no earth, with an IEC plug at the 34 end and a Bulgin socket at the 303 end. You can get one from Flashback Sales in UK or maybe even in the Web shop here.

If you're powering the 303 directly from a wall outlet there is the possibility of an earth loop, and you could try disconnecting the shielding from the 4-pin DIN plug at the 303 end if you can solder.

But it sounds to me like you have poor grounding in your mains outlets. Not much you can do about that except try to find one that doesn't cause the buzz, and either complain to the landlord (as it is a safety issue) or, if it's your property, get an electrician in.

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