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Grounding issues - any experts?

Julf said:
You say you are using coaxial cables without screen connectivity. That is where I would start - the screen is there not just to protect from EMF, but to carry earth currents.
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Yes, that's what I thought hence:

"The chassis on my Benchmark DAC is connected to earth but the DDRC22D and RPI are not. As an experiment I connected the ground of the unused RCA connector on the RPI to earth (so that the cable shields running from the RPI to the DAC (via the DDRC22D) and the chassis of the DDRC22D itself were all grounded) and the system stopped working!"
 
Dougunn said:
Ah! I see your point. Without the Digione my system wont actually work. I have no other way to create SPDIF output.

I may have the old 'standard' Digione I could try . . .

Hmmmm.
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Hi,
The dual supply of the Allo Digione Signature could be an issue, so perhaps using a Hifiberry Digi+ SPDIF card at £32 could be a solution.

The jitter claimed to be solved by the Allo Digione Signature, will not solve anything, since if the jitter of the Benchmark DAC was 500ps, and the Allo Digione Signature is 10ps, then the 500ps jitter will remain in the system. That is, the Benchmark DAC sets the final jitter experienced and the Allo Digione Signature will have no effect.

Regards,
Shadders.
 
Breakthrough!

In line with Yomanze's suggestion above, I have just powered the MiniDSP from a wall wart connected to a different wall socket across the room i.e. not in the Tacima block and voila, the problem is gone!

As to understanding what's happening . . . . . no idea!

Doug
 
Tomorrow I will take it out altogether and review. For now the mains extension across my sitting room is fine!

Thank you all for your thoughts and ideas.

D
 
Good news. I had a hum problem that nearly drove me bonkers trying to find until I realised I had my amps plugged into the wall and the sources via a mains block with a filter. Took that out and problem solved.
 
Dougunn said:
Yes, that's what I thought hence:

"The chassis on my Benchmark DAC is connected to earth but the DDRC22D and RPI are not. As an experiment I connected the ground of the unused RCA connector on the RPI to earth (so that the cable shields running from the RPI to the DAC (via the DDRC22D) and the chassis of the DDRC22D itself were all grounded) and the system stopped working!"
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This is not the same! Just trust me on that one as life's too short for the technical explanation... A proper 75 Ohm coax is what is needed. It's probably a lucky fluke that a different socket works.
 
Dougunn said:
Yes, that's what I thought hence:

"The chassis on my Benchmark DAC is connected to earth but the DDRC22D and RPI are not. As an experiment I connected the ground of the unused RCA connector on the RPI to earth (so that the cable shields running from the RPI to the DAC (via the DDRC22D) and the chassis of the DDRC22D itself were all grounded) and the system stopped working!"
Click to expand...

That sounds like a serious grounding issue!
 
Arkless Electronics said:
This is not the same! Just trust me on that one as life's too short for the technical explanation... A proper 75 Ohm coax is what is needed. It's probably a lucky fluke that a different socket works.
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LOL! Yes, I tried to read up on and understand grounding (signal ground, chassis ground and earth ground etc) but felt my head wanting explode! I do admire the knowledge of guys like you; I'd really like to understand electronics more but it is bewildering where to even start.

I am intrigued however, are you saying that simple 75ohm coax is better than the coax interconnect from Mark Grant? I mean that question in terms of electronic engineering and not audiophile cable nonsense. I thought the Mark Grant cables were pretty standard coax - albeit nicely terminated and finished.
 
Dougunn said:
LOL! Yes, I tried to read up on and understand grounding (signal ground, chassis ground and earth ground etc) but felt my head wanting explode! I do admire the knowledge of guys like you; I'd really like to understand electronics more but it is bewildering where to even start.

I am intrigued however, are you saying that simple 75ohm coax is better than the coax interconnect from Mark Grant? I mean that question in terms of electronic engineering and not audiophile cable nonsense. I thought the Mark Grant cables were pretty standard coax - albeit nicely terminated and finished.
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YES! The important bit (apart from it being connected at both ends which is the real biggy here!) is that it is 75 Ohm coax. Any old RCA lead you have around will probably do if it is connected at both ends. I use normal TV/radio down lead coax for my digital cables as it is indeed 75 Ohm characteristic impedance.
 
Arkless Electronics said:
YES! The important bit (apart from it being connected at both ends which is the real biggy here!) is that it is 75 Ohm coax. Any old RCA lead you have around will probably do if it is connected at both ends. I use normal TV/radio down lead coax for my digital cables as it is indeed 75 Ohm characteristic impedance.
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This is the cable I am using. It does state on the site (on another page) that the cable is 75 Ohm (although my understanding is that RCA plugs are not, so this may be pretty meaningless in terms of the cables overall impedance). I felt it was a pretty standard good quality no foo fit and forget job.

The ground is indeed connected at both ends
 
Dougunn said:
This is the cable I am using. It does state on the site (on another page) that the cable is 75 Ohm (although my understanding is that RCA plugs are not, so this may be pretty meaningless in terms of the cables overall impedance). I felt it was a pretty standard good quality no foo fit and forget job.

The ground is indeed connected at both ends
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Aha... I thought it odd that the ground was not connected at both ends.... sometimes done for ground loop purposes but very wrong if it had been done here.
RCA phono's are in fact pretty close to 75R. Obviously the cable has no effect on sound quality, as is almost always the case.
 
The Canare rcap rca plug is the closest to 75 ohms of any rca plug because it's the only full circular crimp RCA available. All solder plugs use a bucket for centre pin and the shield is tapered to the outer. This asymmetry affects the impedance.

If you want the best digital coax buy a pre-made canare rcap coax cable, from blue jeans, other vendors are available, in the shortest size that reaches. The closer the impedance, and shorter the cable the smaller signal reflections will be.
 
sq225917 said:
The Canare rcap rca plug is the closest to 75 ohms of any rca plug because it's the only full circular crimp RCA available. All solder plugs use a bucket for centre pin and the shield is tapered to the outer. This asymmetry affects the impedance.

If you want the best digital coax buy a pre-made canare rcap coax cable, from blue jeans, other vendors are available, in the shortest size that reaches. The closer the impedance, and shorter the cable the smaller signal reflections will be.
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Indeed. One of the reaons I chose the Mark Grant cable was that it uses Canare crimped plugs
 
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