Humming Noise in my amplifier??? - Page 3

AndrewT · 18th February 2006, 08:06 AM

Hi,
your sketch shows PSU 1 & 2.
Each has a pair of +&- and a GND.
To achieve this, your two transformers must have a common or centre tap.

gmphadte · 20th February 2006, 06:16 AM

Either u have to change the back panel layout or change the placement of the transformer. U are taking the mains wire diagonally and the same is true for audio cable.

Hope u are using regulated psu. What regulators/ckt are u using?

Gajanan Phadte

lock dogg · 20th February 2006, 08:23 AM

Hi,

Sorry but I dont think I have anything that regulates anything, I didnt know I needed all this stuff, could someone please explain what all this stuff is? and how I can actually apply this to my amplifier?

I think my main problem is just the ground loop.

Thanks Stefan

sangram · 20th February 2006, 08:33 AM

Hi Stefan

The reason for a ground loop is because your preamp and one of your channels do not share a proper ground, the only connection between the two is through the shield or ground wire connecting the two.

First you have to create a power ground. This would be the point where the two filter capacitors meet.

Then you create a signal ground. This would be the point where input grounds are tied together. This should be insulated from chassis.

Then you create an output ground. This would obviously where the speakers take their ground connection from.

Using heavy guage wire, connect all the above grounds for both channels to one point. This would be the CSG (Central Star Ground) of the amplifier.

Now this point should be connected to the chassis using a 10 ohm resistor and 1 uF high voltage capacitor (in parallel with each other).

I really can't get clearer than this. Hope it helps you.

The second source of hum would be the transformers inducing hum into the signal area. A bit of clean up in your wiring will help, but I've seen (and done) worse without that creating any major problems.

You do not need to run a regulated supply for power amplifiers. That's a misconception and can create more problems than it solves unless it's well thought through. So don't worry about it.

sangram · 20th February 2006, 08:36 AM

Two more things:

At no point should any of the input jacks be connected to the chassis. This is important to eliminate any ground loops

Also the reason for a ground loop creating hum is the voltage differential between the electrical input of the amplifier and the physical resistance of the electrical path leading to it, multiplied by the gain of the amp. This is why we are striving to create the lowest possible resistance between the input and output grounds.

gmphadte · 20th February 2006, 08:52 AM

For the preamp...
Apart from regulating the dc voltage, the regulators like LM317, LM337 from National, with a small cap at the adj pin, drastically reduce the ripple at the output. The humming noise which u hear could be from power supply also.

If the hum is due to close proximity of the transformer, then try moving the transformer away from the ckt. If this reduces the hum, u have to shield the trannys, may be u should make a separate cabin for them.

Gajanan Phadte

lock dogg · 20th February 2006, 10:01 AM

HI GUYSSSS.....

YOUR PROBABLY WONDERING WHY I AM WRITING IN CAPS LOCK WELLLLLLLLL MY AMP WORKSSSSSSS

YOU WONT BELEIVE how easy the fix was there was nothing really wrong with the ground, well there was but it was a simple cable I had to make from the GROUND of the INPUT of the pre-amp and the cable goes accross to the OUTPUT GROUND. THATS IT NO hum what so ever, I only done it as a guess.

I am sooo HAPPY lol, and I would LOVE to THANK EVERYONE for helping me out, without you guys I probably wouldnt have even looked at ground as a problem , SOOOO THANK YOU soo much everyone. Your all great people...

If you would like more info on how it works just ask.
I will be glad to tell anyone of what I just done lol ( I arent a geneus this was just a TOTAL guess )

THANKS ALOT
STEFAN

AndrewT · 20th February 2006, 02:38 PM

Hi Lock,
are you saying a missing ground (in the preamp) caused the hum?

lock dogg · 21st February 2006, 08:14 AM

Hi,

Welll I dont know cause I noticed that the power and signal ground on the pre map were all connected as one, but when I attched a cable from pre amp input to the pre amp output it made it all better,

The pre amp did have a ground but when it touched the case it made a terrible sound.

Thanks
STefan

gmphadte · 23rd February 2006, 11:33 AM

The siganal ground is taking the easier and shorter path now.

18th February 2006, 08:06 AM	#21
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, your sketch shows PSU 1 & 2. Each has a pair of +&- and a GND. To achieve this, your two transformers must have a common or centre tap. __________________ regards Andrew T.

20th February 2006, 02:38 PM	#28
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi Lock, are you saying a missing ground (in the preamp) caused the hum? __________________ regards Andrew T.

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20th February 2006, 06:16 AM	#22
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	Either u have to change the back panel layout or change the placement of the transformer. U are taking the mains wire diagonally and the same is true for audio cable. Hope u are using regulated psu. What regulators/ckt are u using? Gajanan Phadte

20th February 2006, 08:23 AM	#23
lock dogg diyAudio Member Join Date: Jun 2004 Location: Geelong	Hi, Sorry but I dont think I have anything that regulates anything, I didnt know I needed all this stuff, could someone please explain what all this stuff is? and how I can actually apply this to my amplifier? I think my main problem is just the ground loop. Thanks Stefan

20th February 2006, 08:33 AM	#24
sangram diyAudio Member Join Date: Sep 2002 Location: India	Hi Stefan The reason for a ground loop is because your preamp and one of your channels do not share a proper ground, the only connection between the two is through the shield or ground wire connecting the two. First you have to create a power ground. This would be the point where the two filter capacitors meet. Then you create a signal ground. This would be the point where input grounds are tied together. This should be insulated from chassis. Then you create an output ground. This would obviously where the speakers take their ground connection from. Using heavy guage wire, connect all the above grounds for both channels to one point. This would be the CSG (Central Star Ground) of the amplifier. Now this point should be connected to the chassis using a 10 ohm resistor and 1 uF high voltage capacitor (in parallel with each other). I really can't get clearer than this. Hope it helps you. The second source of hum would be the transformers inducing hum into the signal area. A bit of clean up in your wiring will help, but I've seen (and done) worse without that creating any major problems. You do not need to run a regulated supply for power amplifiers. That's a misconception and can create more problems than it solves unless it's well thought through. So don't worry about it.

20th February 2006, 08:36 AM	#25
sangram diyAudio Member Join Date: Sep 2002 Location: India	Two more things: At no point should any of the input jacks be connected to the chassis. This is important to eliminate any ground loops Also the reason for a ground loop creating hum is the voltage differential between the electrical input of the amplifier and the physical resistance of the electrical path leading to it, multiplied by the gain of the amp. This is why we are striving to create the lowest possible resistance between the input and output grounds.

20th February 2006, 08:52 AM	#26
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	For the preamp... Apart from regulating the dc voltage, the regulators like LM317, LM337 from National, with a small cap at the adj pin, drastically reduce the ripple at the output. The humming noise which u hear could be from power supply also. If the hum is due to close proximity of the transformer, then try moving the transformer away from the ckt. If this reduces the hum, u have to shield the trannys, may be u should make a separate cabin for them. Gajanan Phadte

20th February 2006, 10:01 AM	#27
lock dogg diyAudio Member Join Date: Jun 2004 Location: Geelong	HI GUYSSSS..... YOUR PROBABLY WONDERING WHY I AM WRITING IN CAPS LOCK WELLLLLLLLL MY AMP WORKSSSSSSS YOU WONT BELEIVE how easy the fix was there was nothing really wrong with the ground, well there was but it was a simple cable I had to make from the GROUND of the INPUT of the pre-amp and the cable goes accross to the OUTPUT GROUND. THATS IT NO hum what so ever, I only done it as a guess. I am sooo HAPPY lol, and I would LOVE to THANK EVERYONE for helping me out, without you guys I probably wouldnt have even looked at ground as a problem , SOOOO THANK YOU soo much everyone. Your all great people... If you would like more info on how it works just ask. I will be glad to tell anyone of what I just done lol ( I arent a geneus this was just a TOTAL guess ) THANKS ALOT STEFAN

21st February 2006, 08:14 AM	#29
lock dogg diyAudio Member Join Date: Jun 2004 Location: Geelong	Hi, Welll I dont know cause I noticed that the power and signal ground on the pre map were all connected as one, but when I attched a cable from pre amp input to the pre amp output it made it all better, The pre amp did have a ground but when it touched the case it made a terrible sound. Thanks STefan

23rd February 2006, 11:33 AM	#30
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	The siganal ground is taking the easier and shorter path now.

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