Need help for a beginner - grounding scheme

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Need help for a beginner - grounding scheme (icepower 500asp, 500a)

hey all


beginner/hobbyist here, needed some assistance/guidance from the pros


started getting a really nasty noise that coincided with hdd activity through the speakers



my signal chain: cpu --> udac8 (usb) --> amplifiers


after much debugging, i completely narrowed it down to the usb cable carrying this noise


i modified the cable, it now has no gnd path, still the noise


i believe i solved this when i opened the udac8 up and re-sat all connections, however prior to that, i started digging around my amp wiring and it lead me to here


the first realization i made was that my RCA has no (V-)! (i think?). i originally had the RCA shield tab connected to both AGND and (V-) on the amp, however cutting the V- path seemed to clean up things quite a bit. progress!


however here is the latest. when i have (1) rca connected to the amp from a powered down udac8 (literally nothing connected), quite as a mouse, however when i connect a second rca from udac8 to the amp, i get an increased hum/noise floor


if you guys could validate my wiring diagram, that would be most appreciated!!!


827709d1585153522-help-beginner-grounding-scheme-firefox_nkq5djcmkp-png
 

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First off, it's not a good idea to start ripping everything up because you have a hum problem. Almost always it will turn out to be a bad patch cord or something equally simple.

From your drawing... take the plastic washers out of your RCA connectors and get them on chassis ground, along with your power supply, amplifier boards and any other circuitry. Run microphone cable from the RCA to your inputs with the shield grounded on both ends. It is entirely likely you were picking up hum induction from the case itself.

Get a proper USB cord with the ground intact. It is necessary as a reference for the data lines and the cable won't supply power without it. There's no reason to go exotic, the $6.00 Amazon Basics one will do just fine.

Make sure all your patch cords are shielded, with the shield grounded at both ends and have good continuity. The purists and elitists will yell at me about this but there's just no substitute for good old electrical common sense.


Hope this helps...
 
From your drawing... take the plastic washers out of your RCA connectors and get them on chassis ground, along with your power supply, amplifier boards and any other circuitry.


ok, i will remove the washers. the 500ASP is an amp with integrated power supply, according to the designer manual (see image below) it shows the chassis of the module is grounded effectively on mount. mine is mounted directly to the chassis. however i'm not entirely clear how best to do this with the 500a modules. as you can see (see image below) i have them mounted so the heat sinks are connected to the chassis. are these considered chassis ground? should i be perhaps connecting some wire to the chassis? just some clarification if you could be somewhat specific would be helpful!



Run microphone cable from the RCA to your inputs with the shield grounded on both ends. It is entirely likely you were picking up hum induction from the case itself.


actually, the wiring module that came with the 500asp has this, however the connections to my 500a modules do not. effectively on the RCA end, it has a white that terminates to the (V-), red that terminates to (V+) and the cable shield that is just loose wire however terminates to AGND. i have currently the loose wire connected to the RCA shield (AGND) and the red (V+) to the pole, there is nothing connected to (V-) as this is an unbalanced connection. is this accurate?


Get a proper USB cord with the ground intact. It is necessary as a reference for the data lines and the cable won't supply power without it. There's no reason to go exotic, the $6.00 Amazon Basics one will do just fine.


i have many lying around the house, the USB-mod i did was in hopes to kill any loops (honestly was just a shot in the dark). after switching between multiple cords, i have found there is no difference in noise at this time (even the modded one works just fine)


Make sure all your patch cords are shielded, with the shield grounded at both ends and have good continuity. The purists and elitists will yell at me about this but there's just no substitute for good old electrical common sense.


i think i need some further details here, specifically are you calling patch cords just anything interconnecting?


thanks for the reply!
 

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Ooof indeed. At the risk of getting called for my own inexperience you are provided with the insulating washers, likely keyed to the connectors, because you do not want signal ground to get a sniff of chassis ground, AKA Cooking Earth, because that is the route that all the cr*p takes.

Your system diagram shows the 500A-SP having a, touching, chassis. connection. That will be the primary side earth on the SMPS which is going to be shunting excess high frequency noise into the chassis. You still need it for safety purposes.

Looking at your pictures one thing that is noticeable is that the main 500A-SP board uses a screened cable for its RCA connection. The 500A boards appear to use simple twisted pairs. I would be inclined to implement the same connection on the 500A as you have on the 500A-SP.

I would go further and make use of the differential inputs on all three modules. RCA centre to V+ RCA outer to V- but use a two core screened cable with the screen at the module end connected to AGND and no connection at the other end.

Do the same on all three modules and dress/route the cables so they are not passing over or otherwise close to things, particularly power components/cables.
 
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thanks for the reply, i have read that, but my comprehension simply isnt there to apply the solution to my application. i think my challenge is i have multiple 'hanger' modules that are coming into play here. so putting it all together is challenging for me with my currently knowledge level


Ooof indeed. At the risk of getting called for my own inexperience you are provided with the insulating washers, likely keyed to the connectors, because you do not want signal ground to get a sniff of chassis ground, AKA Cooking Earth, because that is the route that all the cr*p takes.

Your system diagram shows the 500A-SP having a, touching, chassis. connection. That will be the primary side earth on the SMPS which is going to be shunting excess high frequency noise into the chassis. You still need it for safety purposes.

Looking at your pictures one thing that is noticeable is that the main 500A-SP board uses a screened cable for its RCA connection. The 500A boards appear to use simple twisted pairs. I would be inclined to implement the same connection on the 500A as you have on the 500A-SP.

I would go further and make use of the differential inputs on all three modules. RCA centre to V+ RCA outer to V- but use a two core screened cable with the screen at the module end connected to AGND and no connection at the other end.

Do the same on all three modules and dress/route the cables so they are not passing over or otherwise close to things, particularly power components/cables.


ok, so before this latest round of tinkering i had isolated-rca shield terminated to V- and AGND, after snipping V- on one, and AGND on another, i found that leaving V- disconnected provided the best noise floor. also, having since done that, i also am not getting the usb-feedback (passed from cpu, through the udac8, to the rca cables i'm assuming). so i'm not entirely sure why, but it did help


however my biggest issue now is when i have one rca connected, almost dead silent noise floor, add a second in, and a slight uptick in hiss. ive seen some powerpoints on 'bonding rca connections' and wonder if i need to be doing that? also, i'll order up some of that cable to implement as well, not however following the logic of having it open ended
 
Conceptually speaking you separate signal ground, power ground and chassis ground from each other. If they do connect then it should only be at one point with the opportunity to implement what is called a ground lift which places some resistance (100R) between the audio stuff and chassis ground.

That's often difficult or even impossible to achieve. You can have something in which there is what appears to be a ground loop but it isn't because your connections avoid differential signals between what looks like they would be two connections to that loop.

Using the differential inputs on your modules should kill off any idea of such a thing give or take the common mode rejection of the amplifiers which will be upwards of 60dB. The fact that you are connecting a single ended output to a differential input is neither here nor there.. I suppose it is somewhere but that will be back into the source/s.

If you are referring to the open, at one, ended screen then it's there for electrostatic purposes. You might make the differential connection as suggested using just a twisted pair. Try that and see if it cures your problem. However the screen is extra shielding and worth having.
 
The fact that you are connecting a single ended output to a differential input is neither here nor there.. I suppose it is somewhere but that will be back into the source/s.

B&O's manuals for the ICEPower modules say that single ended can be done by shorting the cold (v-) pin to ground at the input connectors then using shielded RCA cables to feed the amp. (Gnd and V+ input)

As a rule running continuity checks between all these grounds usually show's they are all connected together at some point. But I've not played with this on ICE modules.

In fact, had I known this was about ICEPower at the start I would have stayed out of the thread. I really don't know enough about them to be much help.
 
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B&O's manuals for the ICEPower modules say that single ended can be done by shorting the cold (v-) pin to ground at the input connectors then using shielded RCA cables to feed the amp. (Gnd and V+ input)

As a rule running continuity checks between all these grounds usually show's they are all connected together at some point. But I've not played with this on ICE modules.

In fact, had I known this was about ICEPower at the start I would have stayed out of the thread. I really don't know enough about them to be much help.


yeah, this is really the part i'm getting rather confused on


in my diagram above, i have rca shield --> AGND input on amp, and pin --> V+, there is nothing connected to the V-


however, above seems to indicate that i should be mapping rca shield --> V- and AGND on amp, and pin --> V+


thoughts?
 
May I point out to the helpful members -
the op stated he was getting HDD activity noise through his system.
This may not be a hum/grounding issue at all.
I would suggest to the op that he connects his DAC to any other (not DIY) amplifier to test for noise. Test with a single channel before testing multiple channels (fewer connections). I would also suggest he Googles 'HDD noise through audio' as it is quite likely a pc related problem rather than amplifier problem. Also, post in 'digital source' forum on diyaudio. Hope these suggestions help you find a fix.
 
first, i want to thank all of you who have helped!


a quick update before i address the above.



in my desperation, i ripped apart my entire pc, an was running it off a cardboard box to eliminate just about anything i could in the pc (case, unnecessary fans, even pulled the gpu etc..). i also completely removed my DIY amp out of the picture and connected it to an iNuke 3000dsp. same f'in hdd noise. so i ordered an ADUM4160 isloator, took my defeat, and reassembled the pc. after hooking it all back up, so my surprise, no noise (without the isolator, as its still shipping)!!!! now, the only two things i could even think of when i re-assembled are this




  1. i used a different port in my modular pc power supply for my hdd power connection. perhaps the one i had shared something with the mainboard causing it to leak into the USB?
  2. i modified my rca to xlr cables to remove the shield to pin 1 connection. this seemed to reduce some of the noise when it was on the test bench, however this was only to one of the inukes, the other inuke has no modified cable, so i'm thinking this didnt do anything
so, i'm now without any hdd noise in the chain!


however, i'm still at one new issue, and perhaps i need a new thread? not sure


in reference to my first post, in the diagram, my two hanger 500a modules are almost dead quiet with everything off (amp powered, but nothing in the chain on), the 500asp, not so much. i believe i now am receiving a 50/60hz hum in that one and only one module. i haven't fiddled with anything just yet, and not even really sure where to start. so perhaps i'm back to my original diagram, does everything look right? should i bury the earth from the power inlet right to chassis and not hook it into the ASP, perhaps this is where the noise is coming from? any suggestions would be great




Piccy


...


interesting, ok, so the fact that i have nothing in the V- is bad? ha


May I point out to the helpful members -
the op stated he was getting HDD activity noise through his system.
This may not be a hum/grounding issue at all.
I would suggest to the op that he connects his DAC to any other (not DIY) amplifier to test for noise. Test with a single channel before testing multiple channels (fewer connections). I would also suggest he Googles 'HDD noise through audio' as it is quite likely a pc related problem rather than amplifier problem. Also, post in 'digital source' forum on diyaudio. Hope these suggestions help you find a fix.


thanks, i did just that, went to an inuke amp to eliminate as many variables as i could. did a ton of googling, and tried just about everything and then some it feels like!



Maybe try...
see attached..
S

View attachment 828455


i may give it a try, my new issue is a lovely hum in only ONE of the modules (500asp) the other two 500a's are almost dead silent when not in use
 
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