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Seems to be a noisy fan on mb4210 combo

Hi there. i have a newish marshall mb4210 bass combo [ripper] but there's a whirring noise after about 2 mins and then that sound continues. it doesn't get any worse but it's annoying. i was expecting 'near silence' but maybe that's my misjudgement. could be the cooling fan? the whirring is on both channels so i don't think it's to do with the valve in the pre-amp section on classic channel. cannot hear whirring when playing; not terribly loud but when not playing i can hear it from one room away. front of head section of combo does also seem quite warm to the touch so maybe fan not cooling properly. suggestions? thank you very much, james

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The fan is thermally controlled by a temperature sensor. There is NO interference you can fix with shielding. The noise is acoustic and you could try sound deadening. DO NOT block the airflow. This amp is designed to generate a lot of noise so things like fan noise is so far below the listening level the designers don't worry about it. With a 450 watt amp it takes a lot of airflow. The fan is likely throttled and will speed up as heat increases.

Posted on Oct 31, 2011

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Could very well be the fan. The motors can cause interference. There may be a solution to get rid of the noise. Some copper shielding tape may help. You could rule out it being a microphonic preamp tube by turning the amp on as normal and tapping the tubes with something non-conductive. If you hear the tapping noise coming thru the speakers while doing this to a particular tube, replace it. With power tubes, the tops of them turn white on the top when they become microphonic, along with plenty background noise.

Posted on Jun 19, 2009


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