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Transformer humming while using Microwave ?

MasterApex

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I have a Monolith 7x multichannel amp used for driving Atmos surround sound.
I like its sound quality over the multichannel Class D amp ; It is working well and produces good sound.

The power outlet is on the same circuit breaker as one section of my kitchen that has microwave.
I recently notice that when someone is using the microwave, the transformer of Monolith 7x will hum.
The hum is about 47dB loud when you are next to it , so not really audible when you are sitting 10' away with music.

What causes this?

Thanks
 

levimax

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Usually transformer hum is caused by DC on the AC lines... in this case not sure that a Microwave could do that. I would be concerned that you are overloading the circuit, most Microwaves draw about 2000 Watts and it looks like your amp can draw about the same under load.... that is a lot of power for one circuit. Not sure what country you are in but in the US you would probably be tripping the circuit breakers if the music got loud.

If possible I would try another circuit to plug you amp into.
 

Count Arthur

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Usually transformer hum is caused by DC on the AC lines... in this case not sure that a Microwave could do that.

From the article I linked to:

What Causes DC Offset?

The usual suspects that cause DC offset are household dimmers, microwaves, and switching power supplies. Switching powers supplies, which use half wave bridge rectifiers, draw current in uneven pulses. It’s these uneven pulses that can cause large transformers to vibrate and buzz or hum. When a transformer starts to vibrate, it can’t run efficiently and can either won’t function optimally through reduced dynamics or headroom or can cause damage to the equipment.
 

DVDdoug

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I had a similar problem where and amplifier would physically vibrate & hum when the TV was turned-on. So it was either noise or DC or something on the AC line. There was no hum in the audio. (I no longer have that TV).
 
OP
M

MasterApex

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OP
M

MasterApex

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I just order it and will advise if it works
 

Count Arthur

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I've tried one of these, and it definately works: https://www.atlhifi.com/shop/fully-assembled-devices/dc-blocker-trap-filter-assembled-in-case/

If you have an amp with a really large transformer, that needs high current, there's also a larger version: https://www.atlhifi.com/shop/fully-...blocker-trap-filter-2-pcs-us-type-ac-outlets/

You can also buy it as just a PCB if you're handy with a soldering iron.

I built a couple for someone else a while back:

1630893378738.jpeg
 
OP
M

MasterApex

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I just order it and will advise if it works
I got it today
It works to eliminate the transformer hum from the 7x
It has two outlets but can only use one (for 7x) . If I use the open outlet for other device (pre-amp) then the hum is back
So work well for me as I just daisy chain it for just 7x.
 

Count Arthur

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Stealth Silver Solder flex.

Poseur!
LOL, that and the pencil are for scale. :)

Regardless of any supposed sonic benefits of silver solder, the WBT solder is very nice to use, it melts and flows easily and always leaves nice shiny joints - and because I have so much of it, I use it for everything.

I bought that big spool of it some time ago when the ROHS lead free solder directive came about. The lead free solder I've tried is horrible to work with, so I panic bought a life time supply thinking that leaded solder might also be banned for DIY use - turns out it wasn't.

I may have slightly over estimated how much I would get through; at my current rate of use, I should be well over a hunderd years old before I run out. :D
 

Jim Matthews

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I may have slightly over estimated how much I would get through; at my current rate of use, I should be well over a hunderd years old before I run out. :D

I have two rolls, because I couldn't find the first - until I put away the second.
 

Count Arthur

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I have two rolls, because I couldn't find the first - until I put away the second.
I believe that's a quantum phenomenon, whereby objects are able to slip into parallel dimensions, only to be recalled to our dimension by the purchase of a similar object.

Drill chuck keys are particularly susceptible to this.
 

mSpot

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It works to eliminate the transformer hum from the 7x
It has two outlets but can only use one (for 7x) . If I use the open outlet for other device (pre-amp) then the hum is back
Just to be clear, do you mean the transformer hum is back?
That sounds like a ground loop.
A ground loop if the hum is from the speakers, but not if it's transformer hum.
 

Jim Matthews

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A ground loop if the hum is from the speakers, but not if it's transformer hum.

Re-read post #13.

When hum appears using two different outlets, ground loop is a common cause.
 
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