[xenithon]

Yes, I have tried with both amp and DAC connected directly to wall power, bypassing the UPS.

I use a Macbook, and the noise persists whether it is connected to power or on battery. It also persists if I disconnect the Macbook from the DAC - that is, no inputs connected to DAC, analog RCA interconnects from DAC to amp....same type of noise.

 

[Herandu]

Quote:

Originally Posted by xenithon /img/forum/go_quote.gif Let me try that - what part should I touch on the DAC/amp? (housing, rear panel, front panel) Also, just touch with my finger?

Yes to all of them.

 

[Traddad]

Quote:

Originally Posted by 883dave /img/forum/go_quote.gif Could be that your computer is sending digital noise (clicking) down the line. You might want to try a different outlet, maybe even running and extention cord from another part of your residence to different outlets (to make sure the power lines are not run in series)

Done. I ran extensions all over the house. I'm thinking that it's one of the components plugged into the computer (I hope). Or maybe the dimmer switch that's on the same circuit.

 

[xenithon]

Thanks for the clarification Herandu. I tried that - did not help. I also tried using a cable (single analog interconnect) to touch the DAC housing/faceplate/backplate with one end and the other to the amp housing/faceplate/backplate, but it did not help.

 

[Traddad]

How 'bout a wire running from the dac to the center screw on a wall socket (which is usually grounded)

Get someone else's opinion before doing so as I am not an electricion.

 

[Herandu]

Quote:

Originally Posted by xenithon /img/forum/go_quote.gif Thanks for the clarification Herandu. I tried that - did not help. I also tried using a cable (single analog interconnect) to touch the DAC housing/faceplate/backplate with one end and the other to the amp housing/faceplate/backplate, but it did not help.

That indicates that you don't have a floating earth problem. The CDP doesn't produce the hum, because it has a set of muting transistors that cuts the sound out when no signal is present. The DACs don't have any muting transistors.
My suspicion lies with a possible soldering dry joint in the ground path of the preamp section of your amplifier. But to track that down you'll need an oscilloscope and/or good servicing experience.

 

[Traddad]

Quote:

Originally Posted by Herandu /img/forum/go_quote.gif My suspicion lies with a possible soldering dry joint in the ground path of the preamp section of your amplifier. But to track that down you'll need an oscilloscope and/or good servicing experience.

This is a bit counter intuitive to me (of course I'm not an EE). Are you saying the hum comes from the preamp section of the amp.....or the interaction of the amp and the DACs...or from the dacs when the amp doesn't ground? If it's a ground path problem couldn't you test that by grounding the dac to something else? Since the only connection is the two RCAs......
Speaking strictly for my rig, when the computer's hooked up to AC, it hums. When it's hooked up to a battery, no hum. No hum from the powered sub, DVD, TV or CDP. Sorry for the hijack.

 

[xenithon]

Taking a look at the wall plug of the CD player, I notice that the earth pin has no wire connected. Also, you mentioned that the CDP doesn't produce the hum, because it has a set of muting transistors that cuts the sound out when no signal is present. I am not certain about that as it is a very old player (at least 15 years old), and if I put it on pause during playback it is silent. During quiet passages of music there is also no noise.

 

[xenithon]

Hi guys. Ok, I opened the cover of the AC receptacle side of the power cable, and disconnected the wire from the earth pin (is this what you term a cheater plug?). I then connected the DAC and......sweet silence.....dead quite background, no channel imbalance. Does this indicate that it is a ground loop issue?

I know some components can be run without an earth, but virtually all the sites I read about this suggest it is useful to identify the issue and should NOT be used as a permanent solution. In addition, on the back panel of the DAC it states "this device should always be earthed".

So, how would you guys suggest I go about resolving this permanently, and safely?

Cheers
X

 

[Traddad]

Wow, I'd like to hear this answer! I basically did all of the tests last night (unplugged everything but the CPU/DAC) so nothing was on the same plug or even on any plug in the room and I still got the hum. Tried it again with all the same components I used a laptop running on battery and no hum. I also did a little closer listening and
a) the hiss/hum differs with volume
b) it's on both speakers even if I only have 1 RCA plugged in (weird, that)
c) when I hook up the internal sound card (DAC out of the loop) I get much the same hiss/hum.
This is beginning to become really frustrating. I want my music back!

 

[Herandu]

Quote:

Originally Posted by xenithon /img/forum/go_quote.gif Hi guys. Ok, I opened the cover of the AC receptacle side of the power cable, and disconnected the wire from the earth pin (is this what you term a cheater plug?). I then connected the DAC and......sweet silence.....dead quite background, no channel imbalance. Does this indicate that it is a ground loop issue? I know some components can be run without an earth, but virtually all the sites I read about this suggest it is useful to identify the issue and should NOT be used as a permanent solution. In addition, on the back panel of the DAC it states "this device should always be earthed".

What you found out is exactly what turntable phono amplifier users have to battle with. The DAC is already earthed via the ground connection on the RCA cable to the amp. So what you had was two grounds: one on the DAC and one on the amp. By removing the one on the DAC you have now established a common ground via the amp only. It is perfectly safe. You just have to remember to reconnect the earth on the mains plug if you ever use the DAC with an amp that has no earth on its plug.

By the way, CD players were using muting circuits as far back as the early 80's.

 

[xenithon]

I spoke to an associate in the electrical field who does AV installations. He said that there are often ground loops in systems similar to this, with a relatively low voltage source (CDP, DAC, etc.) and a higher voltage handling amp. He suggested that the source(s) should not have earth connected as this causes the ground loop, and that the interconnects between the source and the amp will provide ground. That is, the DAC will be grounded by the amp through the interconnects.

Do you guys agree? Do you think it is safe to run the source sans earth such that it is grounded via the amp?

It would explain why removing the earth got rid of the issue in my system, and also the fact that the CDP which had a dead silent background in my system also has earth disconnected (I checked the 3-pin AC plug and see there is no earth wire, only L and N).

Cheers
X

 

[Traddad]

Just an fyi: I found this source and it seems pretty complete:Ground loop problems and how to get rid of them

 

[xenithon]

Thanks Herandu....seems you posted just as I was typing

So you think it is safe then to have the DAC using a power cable with no earth wire connected, as long as the IC's are connected between DAC and amp? And if so, is there any specific order that the gear needs to be switched on and off? (for example, does the amp have to be on before switching the DAC on)

 

[Traddad]

I found this and I wanted to see what the folks here thought:

"Ground fault interrupterscan be used as replacement for ground connections in three prong receptables according NEC. The NEC requires that three prong receptacles without ground that are protected by GFCI must be labelled as such."

"The NEC, section 210-7(d), and CEC, section 26-700(9), are quite explicit that GFCIs are a legal substitute for a grounded outlet in an existing installation where there is no ground available in the outlet box. But your local codes may vary."

Link"
Methods for breaking ground loop