Hi all,
I noticed a hum / buzz coming from my ML 335 power amplifier that I recently purchased. I measured the frequency and it sounds like 195Hz +/- 5Hz. I had problems with noisy amplifiers before - around 120Hz but it was caused by poor toroidal transformers (all made in China). This is quite old but decent quality amp hence I assume that transformers in it are good quality. I tried it through Tacima CS947 but the hum is still the same. The noise is approx 37dB from 5cm away and 20db from 2.5m away. There is noise coming from the speakers. Strange thing is that I listened to it before the purchase and it seemed quiet...
I noticed a hum / buzz coming from my ML 335 power amplifier that I recently purchased. I measured the frequency and it sounds like 195Hz +/- 5Hz. I had problems with noisy amplifiers before - around 120Hz but it was caused by poor toroidal transformers (all made in China). This is quite old but decent quality amp hence I assume that transformers in it are good quality. I tried it through Tacima CS947 but the hum is still the same. The noise is approx 37dB from 5cm away and 20db from 2.5m away. There is noise coming from the speakers. Strange thing is that I listened to it before the purchase and it seemed quiet...
Try it with shorting plugs on the inputs.
Do you have computers, LED lights, light dimmers, or other electrical/electronic equipment
that can be turned off for testing?
Do you have computers, LED lights, light dimmers, or other electrical/electronic equipment
that can be turned off for testing?
I measured the noise level with everything disconnected from the power amplifier, that is speakers and input. I also unplugged everything around the room (including the rest of hi fi) and fridge in the kitchen so the mains line was as clean as I could make it. The hum comes from inside the amplifier and I presume, as it is inside a closed cabinet, it amplifies the noise. The lights were switched off. The speakers are Dynaudios, so very inefficient... but you can't hear the hum in the speakers.
If there is no volume control in the unit after the inputs, like your amp,
then input shorting plugs are needed for proper testing.
When there is a volume control that affects the levels of all inputs, then
the shorting plugs are not necessary. but are still a good idea for testing.
There is another test you can do, but only if the amplifier does not have an output muting relay.
While listening to the noise, try switching the amp off, and while the power is decaying
but is still there, see whether the noise immediately goes away, or slowly fades out.
If the noise immediately goes away when switching off, the amplifier's main power supply
has a problem that makes excessive rectification noise, and perhaps the main filter capacitors
are going bad.
then input shorting plugs are needed for proper testing.
When there is a volume control that affects the levels of all inputs, then
the shorting plugs are not necessary. but are still a good idea for testing.
There is another test you can do, but only if the amplifier does not have an output muting relay.
While listening to the noise, try switching the amp off, and while the power is decaying
but is still there, see whether the noise immediately goes away, or slowly fades out.
If the noise immediately goes away when switching off, the amplifier's main power supply
has a problem that makes excessive rectification noise, and perhaps the main filter capacitors
are going bad.
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A mechanical noise ? Try some rubber feet.
Place it on the ground / carpet. Does it hum ? Loose screws perhaps ?
Is the transformer humming? It is possible that the mains voltage is too high, the presence of a constant component. Large current consumption. Check the heating of the transformer. Vibration. The rectifier is out of order. Shorting of the transformer winding.
Pay attention to electrical safety.
Pay attention to electrical safety.
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I'm taking it to work tomorrow to see if hums there as well. I took it out from the cabinet today and outside the cabinet (1m away from nearest wall) the hum level drops to 30dB with mic 10mm away from the top cover although still is around 195Hz. 2m away I can't hear it at all...
I will try to arrange some shorting plugs this week.
I will try to arrange some shorting plugs this week.