Dual star ground wiring in mono power supply - diyAudio
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Old 26th November 2011, 07:52 PM   #1
gabdx is offline gabdx  Canada
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Default Dual star ground wiring in mono power supply

Hi everyone,
I am in the process of building a headphone amplifier incorporated to a DAC.
The plan is to build it like the following lampizator project according to this schematic (link to his webpage) : Preamplifier_with_HEAD

I am going to make only a small modification to the power supply by using 3 tube rectifiers, 3 separate transformers and a choke input.

Since I know the interest of a sound ground design I draw some ways to physically build the thing... any advices are welcome, suggestions or questions.

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Old 26th November 2011, 08:56 PM   #2
gootee is offline gootee  United States
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Need to see a schematic!

What type of construction method are you planning to use?

If PCB construction, I would try using a two-sided one and use basically one whole side as a ground plane. If point-to-point, I would also use a bare one-sided PCB with the copper side as a ground plane.

Regards,

Tom Gootee
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Old 30th November 2011, 06:40 PM   #3
gabdx is offline gabdx  Canada
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Hi Tom
I hope this schematic is readeable, I do p2p wiring and it is inside a wooden box.

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Old 30th November 2011, 10:11 PM   #4
gabdx is offline gabdx  Canada
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Second grounding option :

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Old 30th November 2011, 11:07 PM   #5
gootee is offline gootee  United States
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Wow. I'm not really an expert but it looks like asking for trouble, to me, actually.

How about using star grounding?

EACH point to be connected to ground would have its own completely separate conductor that goes all the way back to the single star ground point, by itself. In practice, maybe some similar-signal-type ones could share a conductor. But things like grid input resistor ground reference points' ground-return conductors should never share any length of ground-return conductor with anything else.

Ground-return currents induce voltages across the conductlors' distributed impedances (current times resistance plus rate-of-change of current times inductance), which effectively show up back at the non-ground end of every connected conductor that shares any length of ground-return path with them. For example, for the grid-input ground reference points, that would cause the induced "ground bounce" voltages to be arithmetically summed with your grid input voltages. Not good.

Note, also, that the LOOPS shown in your schematic will also have currents induced in them by any time-varying magnetic or EM fields in the air (AC power, for example), in proportion to the enclosed loop area, and that those currents will induce voltages across the distributed impedance (mostly resistance and inductance) of the loop conductors. Not good. Similarly, a loop can radiate EM fields, too.

Regarding the star ground point: It's often located around the midpoint of the ground connections of the main smoothing caps in the power supply.

Last edited by gootee; 30th November 2011 at 11:32 PM.
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Old 30th November 2011, 11:24 PM   #6
gootee is offline gootee  United States
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How are your "V- DAC OUT" and "V+ DAC OUT" supposed to work?

I'm probably missing something but why aren't they connected across the grid input resistor(s)? i.e. Why aren't the V- DAC OUT signals connected to the ground ends of the grid input resistors?

Also, are they differential signals or single-ended?

Last edited by gootee; 30th November 2011 at 11:29 PM.
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Old 1st December 2011, 07:38 PM   #7
gabdx is offline gabdx  Canada
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Thanks for the reply; I can see that the ground I made is not localized at the capacitor bank but just floating in the middle.
I revised my schematic and put 4 star grounds at capacitors C2, C 3, and C5, C7 decoupling their relative circuit power line. I will post it soon.
To answer your last question, the dac is simply the akm4396 differential output. The reason for connecting the V- to the cathode is to nullify noise by the difference of voltage variation from grid to cathode from one signal to another. Having said that, I can't follow what you mean by ground ends of grid input resistor... I didn’t put a grid input resistor, only a grid loading resistor. There is a cathode resistor of 200R and the V- is connected directly to the cathode so the voltage difference is 5.6 V (2.8V +2.8V) between the grid and the cathode. The cathode effective reference is 0v, there is no cathode resistor to ground to elevate the reference voltage cathode-grid. Thanks for pointing that out because I found a solution to this.
I realized that I won`t use the V- signal because the 200R is too low.
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Old 3rd December 2011, 07:50 PM   #8
gabdx is offline gabdx  Canada
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My last revision. The idea behind it is to use it both as a preamplifier and headphone amplifier. There is 3 separate power supply. One for the dac output and two others for the headphone left and right channels. Now do you see ground loops !? The second picture is an alternative way of grounding the output directly to the capacitor banks, or maybe i should use only of of the capacitor bank...


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Last edited by gabdx; 3rd December 2011 at 08:01 PM.
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Old 4th December 2011, 12:42 AM   #9
gootee is offline gootee  United States
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You probably first need to look at pages 34-36 of the AK4396 datasheet at http://www.asahi-kasei.co.jp/akm/en/...k4396_f00e.pdf . If that is the same chip then the differential outputs need to be low-pass filtered and also converted from differential to single-ended, before you use them. That will give you a signal and signal ground conductor for each channel.
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Old 11th December 2011, 05:10 PM   #10
gabdx is offline gabdx  Canada
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Hi , thanks for pointing this to me. I thought using only the + signal would work, the - signal would not connected.
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