DAC hum

McCrackers · 21st January 2009, 01:41 AM

Using my very limited DIY skills I just put together a DAC that uses two torroidal transformers. The board and the two transformers are mounted on a piece of wood inside a metal case. Contrary to the picture the ground wire is now connected to the case.
I'm quite happy with the way it sounds except for a hum that becomes audible at about 12 o'clock on my amp's volume pot and gets progressively louder as volume is turned up. Fortunately it's only audible when there is no signal(CD on pause) Nonetheless I would really like to eliminate this hum completely. I've tried with another DAC and there is no hum at all which confirms that my DIY DAC is the culprit. Would anyone have an idea how to get rid of this hum?
Thanks

McCrackers · 22nd January 2009, 10:04 PM

Not one reply. Was this the right place to post?

hifimaker · 22nd January 2009, 10:49 PM

Could you describe the hum? Are the transformers buzzing or is the hum heard through your speakers? Most likely a ground loop.

-David

McCrackers · 23rd January 2009, 12:05 AM

Thanks for your reply Hifimaker. The hum is coming from the speakers.
Here is a pic of a similar DAC taken from another forum. The builder added a couple of extra parts between the AC socket and the transformers. I suspected these mystery parts are noise suppressors of some sort. I Googled the P/N and came up with Fujitsu switch board - whatever that is.

hifimaker · 23rd January 2009, 02:15 PM

Oftentimes the problem is a ground loop. If this board has separate signal and PSU grounds and the RCA connectors are touching the case somewhere, you can have a ground loop through your front panel.

Also appliances in your home can cause issues as well. Try different outlets, and turn as much stuff off in your home as possible and test again. Sources I've found are noisy CFL light bulbs and motors.

Have a look at an excellent article on the topic by Kent English on the DIYPass site.

http://www.passdiy.com/pdf/articles/ground-loops.pdf

-David

acid_k2 · 23rd January 2009, 03:21 PM

Quote:

Originally posted by McCrackers
I've tried with another DAC and there is no hum at all which confirms that my DIY DAC is the culprit.[/IMG]

hifimaker is right, check groud connections.

my 2 cents:

The other DAC has the same receiver and dac chip? no?

If no digital source is connected to the DAC (or the source is not powered on), some DAC could makes HF noise, and you can hear that.

Puffin · 23rd January 2009, 07:09 PM

I just re-cased a Dac and I had a teribble buzz. Turned out it was one of the transformers (an EI type) I had tried everything to get rid of it and by chance pressed on one side of the tranny and it went away.

hifimaker · 23rd January 2009, 11:11 PM

Beyond ground loops, sometimes merely turning a transformer 90 degrees can help.

-David

McCrackers · 24th January 2009, 01:35 AM

Thanks - I'll try a couple of your suggestions.
I also read somewhere that a ground loop can be caused by have (one) too many grounds. I'm not sure if I understood correctly but it sounded like: If outputs or some other component is grounded then grounding the earth wire on AC socket could cause a ground loop. I'm a bit reluctant to remove earth ground altogether but I think I'll give it a try just to see.

21st January 2009, 01:41 AM	#1
McCrackers diyAudio Member Join Date: Jan 2009	DAC hum Using my very limited DIY skills I just put together a DAC that uses two torroidal transformers. The board and the two transformers are mounted on a piece of wood inside a metal case. Contrary to the picture the ground wire is now connected to the case. I'm quite happy with the way it sounds except for a hum that becomes audible at about 12 o'clock on my amp's volume pot and gets progressively louder as volume is turned up. Fortunately it's only audible when there is no signal(CD on pause) Nonetheless I would really like to eliminate this hum completely. I've tried with another DAC and there is no hum at all which confirms that my DIY DAC is the culprit. Would anyone have an idea how to get rid of this hum? Thanks

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22nd January 2009, 10:04 PM	#2
McCrackers diyAudio Member Join Date: Jan 2009	Not one reply. Was this the right place to post?

22nd January 2009, 10:49 PM	#3
hifimaker diyAudio Member Join Date: Oct 2003 Location: San Jose	Could you describe the hum? Are the transformers buzzing or is the hum heard through your speakers? Most likely a ground loop. -David

23rd January 2009, 12:05 AM	#4
McCrackers diyAudio Member Join Date: Jan 2009	Thanks for your reply Hifimaker. The hum is coming from the speakers. Here is a pic of a similar DAC taken from another forum. The builder added a couple of extra parts between the AC socket and the transformers. I suspected these mystery parts are noise suppressors of some sort. I Googled the P/N and came up with Fujitsu switch board - whatever that is.

23rd January 2009, 02:15 PM	#5
hifimaker diyAudio Member Join Date: Oct 2003 Location: San Jose	Oftentimes the problem is a ground loop. If this board has separate signal and PSU grounds and the RCA connectors are touching the case somewhere, you can have a ground loop through your front panel. Also appliances in your home can cause issues as well. Try different outlets, and turn as much stuff off in your home as possible and test again. Sources I've found are noisy CFL light bulbs and motors. Have a look at an excellent article on the topic by Kent English on the DIYPass site. http://www.passdiy.com/pdf/articles/ground-loops.pdf -David

23rd January 2009, 07:09 PM	#7
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	I just re-cased a Dac and I had a teribble buzz. Turned out it was one of the transformers (an EI type) I had tried everything to get rid of it and by chance pressed on one side of the tranny and it went away.

23rd January 2009, 11:11 PM	#8
hifimaker diyAudio Member Join Date: Oct 2003 Location: San Jose	Beyond ground loops, sometimes merely turning a transformer 90 degrees can help. -David

24th January 2009, 01:35 AM	#9
McCrackers diyAudio Member Join Date: Jan 2009	Thanks - I'll try a couple of your suggestions. I also read somewhere that a ground loop can be caused by have (one) too many grounds. I'm not sure if I understood correctly but it sounded like: If outputs or some other component is grounded then grounding the earth wire on AC socket could cause a ground loop. I'm a bit reluctant to remove earth ground altogether but I think I'll give it a try just to see.

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