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Old 1st February 2011, 01:06 AM   #51
wlowes is offline wlowes  Canada
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Default Digital and analogue ground

I would tend to agree. I record it here in case someone surfaces with more experience on this to share. I read somewhere the recommendation to separate the ground paths, and to my ears it is good. The tda1541a spec sheet reference circuit hard wires pins 5 and 14 together. What I don't understand is why ARCAM put a cap here. Would not that block DC and allow mhz noise from the digital circuit to pass through? Seems counter intuitive somehow.

I think it was Lucas at the Lampizator site said to think of ground paths as a river where current will follow the path of least resistance to ground. The idea is to let it flow away from the sensitive areas that can most affect the signal.

On a separate note, I have yet to replace the Arcam audio transformer. I have a nice Plitron with an 18-0-18 winding ready to drop in. I hope I get the same results you have seen.
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Old 1st February 2011, 09:02 AM   #52
SimontY is offline SimontY  United Kingdom
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A nice reduction in annoying noises and a cleaner sound should await you!

I think it's time I did some reading about grounds in audio, it's something I don't understand well enough to tinker with right now.
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Old 1st February 2011, 11:36 AM   #53
marce is offline marce  United Kingdom
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Return currents follow different paths depending on their frequency, and at 1mhz and above mostly follow the path of least resistance NOT resistance. This is important when playing with digital as it is imperative to create the smallest loop area for any paticular signal.
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Old 1st February 2011, 12:01 PM   #54
SimontY is offline SimontY  United Kingdom
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Hello Marce,

Is there a typo in your above post?

Do you think there's much to be gained in tweaking this capacitor or changing it for something resistive, inductive or a straight wire link?

Thanks,
Simon
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Old 1st February 2011, 05:06 PM   #55
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Easy to spot the typo:
Quote:
Originally Posted by marce View Post
Return currents follow different paths depending on their frequency, and at 1mhz and above mostly follow the path of least reactance NOT resistance. This is important when playing with digital as it is imperative to create the smallest loop area for any paticular signal.
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Old 1st February 2011, 07:02 PM   #56
SimontY is offline SimontY  United Kingdom
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Thanks!!
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Old 2nd February 2011, 11:42 AM   #57
marce is offline marce  United Kingdom
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woops sorry, path of least inductance.
This link gives a nice overview:
http://www.x2y.com/filters/TechDay09...%20_JohnWu.pdf

I would not use anything resistive to join the two grounds, the aim is to keep them as near to an equipotental plane as possible, so my preference would be a ferrite, but choosing the correct ferrite can be a pain, you nead one to cover the digital noise frequencies.
A good reference for grounding issues are articles (and books) by Henry Ott.
We have similar problems where I work, with digital and analogue, and with so many viewpoints and solutions it is almost impossible to decied which is the best solution.We have tons of fancy equipement, EMC lab etc and can afford multiple re-spins of a product as we have to get it right. What I hope to do later in the year is a analogue digital PCB to test various schemes, such as linear, smps and battery power, different grounding etc, the idea being we have a set of board where the effect of digital (RF) noise on audio can be investigated. I am persuading the powers to be to make this an open source design, and hopefuly let me have some fully populated designs to throw out for others to play with. I am in the initial stages of this, but will start a full thread later in the year.
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Old 2nd February 2011, 02:03 PM   #58
SimontY is offline SimontY  United Kingdom
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Thanks for the link, it looks really helpful!

Your project sounds really good, I'll look out for the upcoming thread.

Question: is there any benefit to adding ferrite beads to ground wires "willy-nilly"? I ask as I added one on my new clock's power supply ground where it joins from its own psu to the main pcb groundplane.

Thanks,
Simon
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Old 2nd February 2011, 03:19 PM   #59
marce is offline marce  United Kingdom
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A common practice is to either use a ferrite or even better a Pi filter (cap, ferrite, cap COG caps are best) to cut noise from one section to another. On a lot of digital and analogue digital it helps limit the general mush on the planes from one section to another. If its a surface mount design there are some nice 3 terminal devices where you can isolate each supply pin.
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Old 2nd February 2011, 07:34 PM   #60
SimontY is offline SimontY  United Kingdom
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Thanks for the info Marce, it gives me something to think about when finding further improvements in my Arcam
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