Loud buzz and hum from one monoblock!!!

victor1 · 12th June 2006, 12:27 AM

I have a problem with one my monoblock (Chinese Mingda-Mc845-C) . As I turned them on today I heard a very loud hum and buzz from my speaker. I disconnected the source ,swapped tubes from a good one and turned it on again. The same very loud hum and buzz. I checked the output signal from the amp. At the very beginning it was 10V then it decreased to 3V. What can it be? All tubes are ok.

Jeb-D. · 12th June 2006, 01:31 AM

If it's a 60 or 120 cycle hum, it's most likely caused by a grounding issue(such as a ground loop) or ripple in the power supply. Also make sure it's not located right by something that may cause interference like a TV.

poobah · 12th June 2006, 01:35 AM

You may have had a diode failure in your power supply too. Are they tube rectifiers or SS?

victor1 · 12th June 2006, 06:54 AM

I can't be ground hoom because I use cheater-plugs.
The amps have solid state rectifiers.

poobah · 12th June 2006, 02:53 PM

Just a guess... but maybe you popped a rectifier...

Does it make any music at all?

Jeb-D. · 12th June 2006, 05:32 PM

Yeah, you'll just have to check the rectifier, supply caps and inductor(may not have one but most SET amps do). And if it's fixed bias check the DC supply to the grid, to make sure thats clean as well. Check each stage because they may have different power supplies. If you have to replace the rectifier I suggest HEXFRED diodes, they have a soft recovery, wich will reduce any spikes in the supply if there are any.

12th June 2006, 12:27 AM	#1
victor1 diyAudio Member Join Date: May 2005 Location: Toronto	Loud buzz and hum from one monoblock!!! I have a problem with one my monoblock (Chinese Mingda-Mc845-C) . As I turned them on today I heard a very loud hum and buzz from my speaker. I disconnected the source ,swapped tubes from a good one and turned it on again. The same very loud hum and buzz. I checked the output signal from the amp. At the very beginning it was 10V then it decreased to 3V. What can it be? All tubes are ok.

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12th June 2006, 01:31 AM	#2
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	If it's a 60 or 120 cycle hum, it's most likely caused by a grounding issue(such as a ground loop) or ripple in the power supply. Also make sure it's not located right by something that may cause interference like a TV.

12th June 2006, 01:35 AM	#3
poobah diyAudio Member Join Date: Nov 2005	You may have had a diode failure in your power supply too. Are they tube rectifiers or SS?

12th June 2006, 06:54 AM	#4
victor1 diyAudio Member Join Date: May 2005 Location: Toronto	I can't be ground hoom because I use cheater-plugs. The amps have solid state rectifiers.

12th June 2006, 02:53 PM	#5
poobah diyAudio Member Join Date: Nov 2005	Just a guess... but maybe you popped a rectifier... Does it make any music at all?

12th June 2006, 05:32 PM	#6
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	Yeah, you'll just have to check the rectifier, supply caps and inductor(may not have one but most SET amps do). And if it's fixed bias check the DC supply to the grid, to make sure thats clean as well. Check each stage because they may have different power supplies. If you have to replace the rectifier I suggest HEXFRED diodes, they have a soft recovery, wich will reduce any spikes in the supply if there are any.