How to nullify AMP's Humming?

[bijinmb]

Seeking help from all the FM's knowledge/experience on this particular topic of "How to nullify AMP's Humming" and make it almost dead silent.

Please share your thoughts/methods or the mandatory steps we should take care to deal with hum.

 

[anilva]

There are many reasons why hum takes place. Could be ground loops or ripple from the power supply. Depends on what sort of hum you are try to remove. So much has been written on hum everywhere and each ones case is unique, but basic principles of avoiding earth loops and ripple current filtering are mandatory.

 

[bijinmb]

There are many reasons why hum takes place. Could be ground loops or ripple from the power supply. Depends on what sort of hum you are try to remove. So much has been written on hum everywhere and each ones case is unique, but basic principles of avoiding earth loops and ripple current filtering are mandatory.

For my build i have a central transformer which has 36-0-36, 18-0-18, 9-0-9 taping which powers amp, vu meter driver, speaker protection respectively.

My few questions are as follows:

1. Can I ground all the zero's of each taping to a common ground?
2. Is there anything specific to be taken care while mounting toroidal transformer?
3. For VU meter driver I am taking signal level input to the VU driver, but in that mode its creating more hum.
   how can i tackle this? putting a diode before the VU driver in the signal path do help ?
4. From RCA I am using two core shielded wire where the signal comes through the two cores and i left the shield wire at RCA end open and the other end to the ground of the AMP's PCB.

 

[mbhangui]

For my build i have a central transformer which has 36-0-36, 18-0-18, 9-0-9 taping which powers amp, vu meter driver, speaker protection respectively.

My few questions are as follows:

[*]Is there anything specific to be taken care while mounting toroidal transformer?

Insure that the bolt that runs through the center is open (insulated) at the other end. Else you will form a loop which will act like a secondary and draw current.

Do you get hum if the AMP input is disconnected from all wires?

 

[bijinmb]

Insure that the bolt that runs through the center is open (insulated) at the other end. Else you will form a loop which will act like a secondary and draw current.

Do you get hum if the AMP input is disconnected from all wires?

Have to check that. but i played the amp outside the cabinet when i bought the kit just for testing.. that time was perfect..all happened when i placed inside the cabinet.

Regarding the transformer mounting the present situation is there is a round disk plate over the transformer and underneath that there is a rubber packing between the coil and the plate. and the bolt is having contact with that metal plate and that bolt is coming down to the base of the cabinet and it has contact there as well. So that needs be open (insulated) right?

 

[jetlag]

Hi
The best way to get rid of ground loops is to ground it only at one end and preferably at the source. This for sure works always. In your case remove the shield from the RCA on the side.

Later
Peace
Jetlag

 

[captrajesh]

Hum can get induced from other gear too. For example, my Cayin runs dead silent as long as the CDP is the source. The moment I route the signal from the CDP through the DAC, there is distinct hum.

However, my Class D amp doesn't have any issues with the DAC.

Wonder why?

 

[mbhangui]

Have to check that. but i played the amp outside the cabinet when i bought the kit just for testing.. that time was perfect..all happened when i placed inside the cabinet.

Regarding the transformer mounting the present situation is there is a round disk plate over the transformer and underneath that there is a rubber packing between the coil and the plate. and the bolt is having contact with that metal plate and that bolt is coming down to the base of the cabinet and it has contact there as well. So that needs be open (insulated) right?

Just see how omishra has mounted the torroid. The top end is totally insulated so that even if the bolt is making contact with the bottom plate, there is no chance of the top end touching the top of the amplifier case and have a shorted secondary.

Also read the article on hum coming to the transformer.

 

[bijinmb]

Hum can get induced from other gear too. For example, my Cayin runs dead silent as long as the CDP is the source. The moment I route the signal from the CDP through the DAC, there is distinct hum.

However, my Class D amp doesn't have any issues with the DAC.

Wonder why?

Captrajesh, but this happens even without connecting to any audio source, keepikng RCA just naked. and i tried with tuner and my dac and getting the same hum...

 

[omishra]

Captrajesh, but this happens even without connecting to any audio source, keepikng RCA just naked. and i tried with tuner and my dac and getting the same hum...

How much is that? I mean your hear it while your ear to speaker or its when we hear without/bad filter caps.

 

[bijinmb]

How much is that? I mean your hear it while your ear to speaker or its when we hear without/bad filter caps.

I can hear that hum even from 1-1.5 meters away from the speaker.
Omishra, when you said bad filter caps, i will check that area tonight whether its of the caps. and also need to mount the toroidal in that top and bottom insulated way. presently its not like that.

 

[soundnovice]

browse thro Rod Elliott's pages. you may find the solution. his articles discuss solutions for practical problems that an average DIYer faces!

 

[captrajesh]

Captrajesh, but this happens even without connecting to any audio source, keepikng RCA just naked. and i tried with tuner and my dac and getting the same hum...

The issue is with the amp then. My post was for two purposes.

1. Suggestion to check if the issue could be elsewhere.

2. Piggy back (not hijack) on your thread with a fond hope of getting suggestion from someone on how to go about to eliminate the problem.

 

[omishra]

Have to check that. but i played the amp outside the cabinet when i bought the kit just for testing.. that time was perfect..all happened when i placed inside the cabinet.

Regarding the transformer mounting the present situation is there is a round disk plate over the transformer and underneath that there is a rubber packing between the coil and the plate. and the bolt is having contact with that metal plate and that bolt is coming down to the base of the cabinet and it has contact there as well. So that needs be open (insulated) right?

So bringing it inside created problem. May be input is getting EMI from transformer. Does your transformer has static shield? If yes then is it open or earthed?

That top metal plate is okay until it not shorting else where. Now that metal plate is considered as part of another end of bolt. That must be suspended in air without touching any chassis/metal part.

I can hear that hum even from 1-1.5 meters away from the speaker.
Omishra, when you said bad filter caps, i will check that area tonight whether its of the caps. and also need to mount the toroidal in that top and bottom insulated way. presently its not like that.

Okay so then Anil pointed it out correctly.

1. Power Supply ripple.
2. Check grounding, earth and PS '0' need not be mixed. IN case of stereo, check for individual channels, disconnect all common wires between both channels. Then power one at a time. At any point no 2 paths of ground coming together.

More information on Amp topology/pic will help us to think.

 

[bijinmb]

So bringing it inside created problem. May be input is getting EMI from transformer. Does your transformer has static shield? If yes them is it open or earthed?

That top metal plate is okay until it not shorting else where. Now that metal plate is considered as part of another end of bolt. That must be suspended in air with touching any chassis/metal part.



Okay so then Anil pointed it out correctly.

1. Power Supply ripple.
2. Check grounding, earth and PS '0' need not be mixed. IN case of stereo, check for individual channels, disconnect all common wires between both channels. Then power one at a time. At any point no 2 paths of ground coming together.

More information on Amp topology/pic will help us to think.

I got few valuable points from you all and many thanks for that, i will try out those things tonight and if that too fail i shall post the images as well for the reference.

 

[vin_eme]

Bijin,

My suggestion would be to disconnect all secondaries (spk protection, vu meter) of the trafo. Just keep the amp power alone. See if you get the hum.
Then isolate any ground loops as anilva and others mentioned. Make sure all inputs sources wires from RCA plug's are shielded (2+1 wire)
. Then check for caps Last.

______________________
**Wirelessly posted**

 

[bijinmb]

I just removed the vu's , speaker protection, and mounted the transformer keeping top and bottom contacts isolated by putting rubber washer on either side and wrapping the bolt with insulation tape.

Now hum has been reduced to normal level, but another issue just pop up (I donno whether it was there before also but i haven't noticed that).

The hum is happening only when i connect Left and Right RCA from the DAC or Tuner.

And when i remove either right or left signal to RCA by unplugging the male RCA the AMP's hum disappears.

Any idea/thoughts?

 

[captrajesh]

I found this thread on hum in a vintage amp. The situation is different but there are some suggestions which may also be relevant in your case.

 

[omishra]

Now hum has been reduced to normal level, but another issue just pop up (I donno whether it was there before also but i haven't noticed that).

The hum is happening only when i connect Left and Right RCA from the DAC or Tuner.

And when i remove either right or left signal to RCA by unplugging the male RCA the AMP's hum disappears.

Any idea/thoughts?

Now its 100% ground loop, your ps and dual mono conguration causing loop it through source ground. It's taking path of input wire ground lead. Easy to fix.

Further help is impossible on any hypothetical amplifier.

 

[anilva]

I think I forewarned you You have so many suggestions from everyone, it is just impossible to debug the problem now.

Each one on his own when it comes to debugging hum for his setup. Other option which is successfully followed in diya forum is posting pictures and have others look at it and suggest. Hum is one of the most dreaded things for me. I can deal with circuit faults but not hum, because it disrupts all the wiring and layout plans.

Best thing is to follow basics and eliminate one by one.

All the best.

Cheers.