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Attention: Marantz 300DC Owners

MaestroSeven

MaestroSeven

Member
I own a 300DC and have a question about a humming I am hearing coming from the amp. I am not sure if this is a problem or just normal operational sounds.

When I first turn the amp on and have no sound source coming through the unit, I can hear a slight hum coming from the unit. Almost like the same sound that would come from an electrical box on the street corner. Again it is only slight and can only be heard when no source is being played (or selected).

Any thoughts would be much appreciated.

This unit has just recently been refurbished in the last 6 months.
 
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Humming could be a grounding problem. Or, it could be a cap in the audio path that is beginning to short. If it gets progressively worse over time, its probable a bad cap. My two cents!
 
If the hum is from the unit itself and not through the speakers, then its a mechanical noise from the power transformer (try tightening the screws on it). If you hear the hum through the speakers then you have bad electrolytic caps in the power supply (the 300 is DC coupled: no caps in signal path).
 
Leestereo said:
If the hum is from the unit itself and not through the speakers, then its a mechanical noise from the power transformer (try tightening the screws on it). If you hear the hum through the speakers then you have bad electrolytic caps in the power supply (the 300 is DC coupled: no caps in signal path).
Click to expand...

The mains are in the signal path.
 
I have four 300dcs, and none of them hum. It is not normal for that model to hum! :no: :D

I agree with Leestereo; if it sounds like a corner electrical box, emanating from the unit itself (not the speakers), then it is almost certainly transformer hum you are hearing. That is exactly the kind of noise you fear from those boxes! You can try tightening the screws on the transformer, to see if you can tighten it up enough to stop the hum (vibration of plates).
 
Transformer hums can also be caused by AC line noise....

Trying plugging the unit into the other Phase of the AC Company power in your house.... You might find that the one phase is dirty due to some thing in you house or even your neighbors house.

I had this issue with one of my 4400s... something in the house would turn on and its transform would start to mechanically hum.....

For a few years now I use powers conditioners, filters and dedicated power runs. Cleans up the audio sound and will protect the units for AC source noise...

But pick you power conditioning wisely... High wattage amps need lots and lots of PEAK not RMS current from the AC supply.

johnk
 
It is definitely not coming from the speakers but is eminating from the amp itself.

I will try to tighten the scews on the transformer. A little nervous to do this but will give it a shot.
 
So this is a mechanical hum? It this is new also check to see if the transformer or filter caps are unusually hot?

charles
 
I have tightened the screws on the Secondary Dual Power Transformer. The huge black unit you see as soon as you open the chasis. The hum is still there and is indeed coming from this transformer.

So I guess then it is my understanding based on what you are all saying that there should be NO hum coming from this transformer whatsoever?
 
How hot does unusually hot have to be? My amp has always ran hot but it is my understanding that they all do. It is well ventilated however.


airtime said:
So this is a mechanical hum? It this is new also check to see if the transformer or filter caps are unusually hot?

charles
Click to expand...
 
How do I locate the other Phase of the AC Company power in my house?


jstang said:
Transformer hums can also be caused by AC line noise....

Trying plugging the unit into the other Phase of the AC Company power in your house.... You might find that the one phase is dirty due to some thing in you house or even your neighbors house.

I had this issue with one of my 4400s... something in the house would turn on and its transform would start to mechanically hum.....

For a few years now I use powers conditioners, filters and dedicated power runs. Cleans up the audio sound and will protect the units for AC source noise...

But pick you power conditioning wisely... High wattage amps need lots and lots of PEAK not RMS current from the AC supply.

johnk
Click to expand...
 
Go to the breaker box... Locate the Circuit Breaker you current have the unit on.

The Breaker Box will have a schematic that should show how the breakers are connected to each of the two phase ( AKA: Hots ) that come into the house...

Locate a circuit and outlet that is on the other phase and is close enough to plug the unit into.

This can all be done by knowing your house, the breaker that serve the rooms and looking at the Service Box schematic... NO NEED TO OPEN THE SERVICE BOX....

You could just pick the amp up move to a different outlet. Or try a heavy duty extension cord... just to see if the HUM goes away once its powered up.

More than likely a different room.

If the HUM seems to shut itself off from time to time.... Could be mechanical loose transformer... But could be a Noisy device on the AC source....

jk
 
MaestroSeven said:
How hot does unusually hot have to be? My amp has always ran hot but it is my understanding that they all do. It is well ventilated however.
Click to expand...

My 300DC doesn't run hot. Hopefully your transformer windings are not delaminating, a problem which cannot be fixed.
 
If it is a standard two prong plug try reversing the way you have it plugged into the current outlet.
 
MaestroSeven said:
What I meant to say is that my 300DC runs hotter than my 2245. Surely that is normal is it not?
Click to expand...

I would say medium-cool is about normal running temp for my 300DC. If yours is hot to the touch, your transformer is converting energy into excessive heat and that is never good. Heat is the enemy!

Get you 300DC checked out and reset to factory specs. That should cool things down a bit.
 
Just to update this. I have tried plugging it into the other phase. I am still getting the same very low slight hum from the transformer...

Would a power conditioner help?

jstang said:
Go to the breaker box... Locate the Circuit Breaker you current have the unit on.

The Breaker Box will have a schematic that should show how the breakers are connected to each of the two phase ( AKA: Hots ) that come into the house...

Locate a circuit and outlet that is on the other phase and is close enough to plug the unit into.

This can all be done by knowing your house, the breaker that serve the rooms and looking at the Service Box schematic... NO NEED TO OPEN THE SERVICE BOX....

You could just pick the amp up move to a different outlet. Or try a heavy duty extension cord... just to see if the HUM goes away once its powered up.

More than likely a different room.

If the HUM seems to shut itself off from time to time.... Could be mechanical loose transformer... But could be a Noisy device on the AC source....

jk
Click to expand...
 
If it does it 100% of the time, I kind of doubt its power rated. You could try turning off breakers in the house for other circuits, to try to rule out another device in the house. ( Wife might not like idea...just tell her its all in the name of science...)

That way you do not spend the $$$ for no reason. But I do filter the supply to the amps to help reduce background noise.


jk
 
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