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  Reply # 1066234 15-Jun-2014 21:56
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Aredwood: The audio ground and the mains ground will be connected together inside the crack amp. And inside your PC. this means you have a loop that starts at the multi box or your houses earth wiring, runs to the case of your PC, through the ground wire in your audio cable to the crack amp. Out the crack amps power cable back to the multi box / house wiring. Using the laptop breaks the loop because Laptop power supplies even if they are 3 pin normally don't carry the ground connection through to the laptops chassis connection. 

Try the ground loop isolator from trademe to verify that it is a ground loop problem. If you don't want to use it permanently. The best way (I think) is to modify the crack amp. What you need to do is have separate audio ground and mains ground. Connect the metal panels, Transformer case ect to the earth pin On the crack amp. Insulate the ground of the RCA connections and the headphone connections from the case if not done already. Make sure that no other audio grounds are connected to the case. Get a high current bridge rectifier such as http://jaycar.co.nz/productView.asp?ID=ZR1324&w=bridge+rectifier&form=KEYWORD Connect the +and - terminals together. And the 2 AC terminals together. Then connect 1 side to your audio ground. And the other side to the mains ground. This will block any small circulating currents because the diodes in the bridge rectifier will only start conducting if there is more than 0.5V difference. But if mains power somehow livens the audio ground, The diodes which can handle 70A (2X35A in parallel) will easily conduct it to ground so the circuit breaker / fuse will still cut the power as normal.


Thanks for the detailed reply. I sort of understand SOME of that. I am not sure I'd have the technical knowledge to undertake the modification to the crack amp, though it sounds like the best way to go, without idiot proof instructions, with pictures etc. I presume all these changes would then change the resistance and voltage checks, so I'd have no way of knowing what they should be. 

I will send off your very useful suggestion to the manufacturer of the kits and see what they have to say.

I think I say you say you are a sparky by trade, is there an idiot proof (read safe) way to check that the "house" is grounded?

Also I'd want to ensure that any changes I made to the Crack Amp would not change it sonically. 


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  Reply # 1066236 15-Jun-2014 22:03
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Niel: .....I would not use an isolation transformer, although it will likely work.  The reason being that you loose your neutral reference so your gear is essentially floating and the RCD in your switchboard will not work (assuming you have one).  Isolation transformers are intended for improving safety in some specific situations (for example accidentally drilling into live wires), not for fixing audio earth loops.


I used to do sound for several bands and always had the audio equipment on stage powered via a rather large isolation transformer for this very reason, something I inherited when I first started.

Florecent light bulbs can often be the cause of annoying buzzes, something every house has plenty of these days. And of course, never run power and audio cables in parallel for too long either..

 
 
 
 


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  Reply # 1066240 15-Jun-2014 22:10
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networkn: Picture of the Crack AMP PSU Area: 

https://www.dropbox.com/s/xeehllzo0j18x0w/20140615_202252.jpg


That picture scares me.




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  Reply # 1066253 15-Jun-2014 22:26
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richms:
networkn: Picture of the Crack AMP PSU Area: 

https://www.dropbox.com/s/xeehllzo0j18x0w/20140615_202252.jpg


That picture scares me.


Why ? 


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  Reply # 1066257 15-Jun-2014 22:31
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networkn:
Why ?


Mains wiring with uncovered connectors in close proximity to low voltage stuff, ugly soldered connections on the quick disconnects with no heatshrink or sleeve over them for a start.

Not too sure on how that earth connection looks, but it looks like its going straight over to something under the capacitor which is dangerously close to the toggle switch connections.






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  Reply # 1066274 15-Jun-2014 22:36
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My 2 cents worth.....

Grounding of each power supply into say a power board may be fine.... but you are looking at perhaps mVs of noise from complex power supplies inducing unwanted noise into inputs of amplifiers.

 

I have seen mains ground loop problems solved by simply re-arranging the order of plugs on power boards (on a lucky day).

Hence the suggestion by others of using an isolation transformer for diagnostics to stop strange currents from causing induced mVs of noise into unwanted places.

Cheers






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  Reply # 1066275 15-Jun-2014 22:39
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Another thing that can help is to run any antenna cables to any interconnected equipment thru something that grounds the shield away from the equipment, as any loops thru the tv/reciever etc will be close to the analog output jacks so make it worse. A cheap powerstrip with antenna surge protection will connect the antenna ground and the power ground together. Or just unplug the antenna altogther.




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  Reply # 1066284 15-Jun-2014 22:53
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Well I won't be doing any more tonight. I just gave myself 240v through the chest trying to get a closer picture. Not sure what I was thinking etc. Not sure how it happened either a bit shaky. The RCD tripped and I dropped the crack amp so it's bent a few things, will require a full check over tomorrow.  I don't recall touching both hands to the metal but I can't see any other way it could have happened. The power switch on the crack amp was turned off, but stupidly (though it didn't occur to me at the time), I had the power cable in. 



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  Reply # 1066286 15-Jun-2014 22:54
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richms: Another thing that can help is to run any antenna cables to any interconnected equipment thru something that grounds the shield away from the equipment, as any loops thru the tv/reciever etc will be close to the analog output jacks so make it worse. A cheap powerstrip with antenna surge protection will connect the antenna ground and the power ground together. Or just unplug the antenna altogther.


I am not sure what you are saying here I'm afraid. What antenna cables and what interconnected equipment?




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  Reply # 1066303 15-Jun-2014 22:58
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richms:
networkn:
Why ?


Mains wiring with uncovered connectors in close proximity to low voltage stuff, ugly soldered connections on the quick disconnects with no heatshrink or sleeve over them for a start.

Not too sure on how that earth connection looks, but it looks like its going straight over to something under the capacitor which is dangerously close to the toggle switch connections.




Well I am not sure what parts you are describing really, but ouch, was my first electronics project in 25 years. I thought I did alright, but clearly not. 

Nothing in the instructions called for heat shrinks or sleeves. 

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  Reply # 1066330 15-Jun-2014 23:26
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networkn:
Comments in other places indicated if I connected the DAC to the PC via Toslink the Ground shouldn't be a problem, but same thing happens. Unsure if that helps. 


Can you explain a little more in detail. Toslink from PC SPDIF to DAC? No other cable connected between them?

Sounds like an earth problem between DAC and 3-pin AMP then, nothing to do with PC. Could be the AMP, could be the power supply for the DAC.

This is why I hate unbalanced consumer audio equipment period ;o)

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  Reply # 1066332 15-Jun-2014 23:42
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Antenna being going to a home theater reciever, TV, etc that is connected to the same computer or DAC somehow, also USB cables carry a chassis ground so unplug any of those going off to external drives and printers etc that are powered seperatly.




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  Reply # 1066335 15-Jun-2014 23:51
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kiwirock:
networkn:
Comments in other places indicated if I connected the DAC to the PC via Toslink the Ground shouldn't be a problem, but same thing happens. Unsure if that helps. 


Can you explain a little more in detail. Toslink from PC SPDIF to DAC? No other cable connected between them?

Sounds like an earth problem between DAC and 3-pin AMP then, nothing to do with PC. Could be the AMP, could be the power supply for the DAC.

This is why I hate unbalanced consumer audio equipment period ;o)


Hi 

Yes Toslink from the PC to the DAC (Nothing else) , then RCA from DAC to AMP. 

If it were a problem between DAC and AMP, then it would be strange as I have tried two DAC's to the same AMP, and they both have the problem. One (ODAC) Is USB only, and other takes COAX Spdif, Toslink and USB, all exhibit the same issue.

With the ODAC to the Crack, the problem doesn't start until it gets plugged into the PC.



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  Reply # 1066337 15-Jun-2014 23:52
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richms: Antenna being going to a home theater reciever, TV, etc that is connected to the same computer or DAC somehow, also USB cables carry a chassis ground so unplug any of those going off to external drives and printers etc that are powered seperatly.


Ok. I did all that already in the troubleshooting in my OP. I don't have any gear not listed, connected (Unless you are talking indirectly as in, on the same electrical circuit in the house).

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  Reply # 1066339 15-Jun-2014 23:58
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When you connect the cable to the PC, you are creating another ground loop. Also chances are the output devices on the DAC are not active when there is no signal coming into them.

What do you get if you have the DAC plugged into the PC but the PC is powered down or in sleep? Still get the noise?

Looking at the design of it I can see why they sell it as a kit - they would be sued out of existance in no time selling something that poorly made pre-built.




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