Murdock

EzMEQ-5 hum
« on: April 04, 2020, 08:44:29 AM »
Hey folks,

I've build an AML ezMEQ-5 some time ago but never really tested it... 
Today I wanted to do that and noticed a quite loud hum/buzz.
I experimented with the power transformer orientation and some mumetall sheets. The buzz gets worse when I turn up the two potentiometers clostest to the PT. If I put some mumetal between the PT and the inductors it gets better, but still not completely...
So there is some magnetic radiation into the two inductors. 
But I'm quite sure, that there is something else on my part as I'm sure Colin from AML tested his build thoroughly before releasing it. And I didn't read any other threads with this problem. I suspect there is a grounding problem.
I also have the buzz when only connecting the output into my mixer with no input...
Here is a link to the build manual with the schematic at the end.
http://www.audiomaintenance.com/downloads/ezmeq5_colourbook.pdf

Can someone maybe see where I could start checking for the fault?


Rob Flinn

Re: EzMEQ-5 hum
« Reply #1 on: April 04, 2020, 09:59:23 PM »
I suspect there is a grounding problem.

Can someone maybe see where I could start checking for the fault?

You seem to have answered your own question.   Very likely a grounding problem.
regards Rob

Murdock

Re: EzMEQ-5 hum
« Reply #2 on: May 04, 2020, 04:39:49 PM »
You seem to have answered your own question.   Very likely a grounding problem.


Yes, but does anybody have a tip on where I could start to look for the problem?
Is there a "common" solution I could try? 

Rob Flinn

Re: EzMEQ-5 hum
« Reply #3 on: May 05, 2020, 05:38:37 AM »
Normally the AML projects have some of the best documentation ypu can get, so you could just go back through the manual & check that you have done everything correctly.

However if you don't want to do that, normally with this sortof problem I would set my meter to continuity, and check that the ground connections match that of the circuit diagram.

regards Rob

Murdock

Re: EzMEQ-5 hum
« Reply #4 on: May 06, 2020, 09:40:47 AM »
Normally the AML projects have some of the best documentation ypu can get, so you could just go back through the manual & check that you have done everything correctly.

However if you don't want to do that, normally with this sortof problem I would set my meter to continuity, and check that the ground connections match that of the circuit diagram.

Thanks for the tip!
I checked with my multimeter and got 10 ohms between TP16 (Analogue ground) and chassis. So this seems to be ok. I just realized, that even without the power plug and just the output connected to the mixer I get a slight buzz (I think 120Hz). And it gets worse when powering up the unit ... Any clue on what could cause that?
I thought ground loops are are pretty much impossible with transformer balanced gear?

Rob Flinn

Re: EzMEQ-5 hum
« Reply #5 on: May 06, 2020, 12:39:42 PM »
Are you sure it's the unit and not your external wiring ?    Have you tried disconnecting the shields on the connecting cables ?
regards Rob


 

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