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Old 23rd May 2012, 10:39 AM   #11
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Thanks qusp for answer. So you mean to connect transformer secondaries in parallel to get double current with the same voltage? You see I have a problem, no earth ground at IEC in my home. So basically I need to deal with just insides of the case.

There is a scheme at the internet with connection between transformer and LM317 LM337 bipolar supply.

Click the image to open in full size.

That is what I'm talknig about.

And a few questions about common ground. Will the ODAC use PC ground from USB line, wouldn't it be enough? And if I connect analog The Wire and PGA2320 ground, wouldn't this cause interference, noise, decrease in performance?

And BTW with center tap PGA and The Wire will have a common ground.
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Old 23rd May 2012, 12:01 PM   #12
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Here is the power related componets I have for this project. Remember, I have no earth ground at home. I know it is bad, but have nothing to do with it.

Can someone draw how should I connect them to maintain a proper grounding techniques?

Click the image to open in full size.

About the ODAC. Here is a close up picture and I see no ground connectors here (besides audio signal of course).

Click the image to open in full size.
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File Type: jpg odac.jpg (300.8 KB, 548 views)
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Old 23rd May 2012, 12:07 PM   #13
qusp is offline qusp  Australia
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look at the PSU you have for the wire, it has 4 holes yes? nothing parallel just connect the 4 wires, in the same order they exit the transformer from left to right from the 2 secondaries, done. this actually puts them in series, not parallel as the 2 middle wires will be connected at this point on the PCB to make a center tap. but do not connect that point also to ground of the wire, just leave it, the center will be effectively at about the same reference voltage as ground as it exists in this circuit, but that point in the middle before the bridge there will have quite a bit of noise. the line that goes down the middle of your schematic there is the ground line you want to use for analogue ground. better just use it as star ground for the whole build since you dont actually have access to ground.

not a chance would I be using your PCs USB ground to reference the build off, I havent looked at the ODAC schematic, but I would doubt hes used it directly for the dac ground either. better ask RS to confirm, but I wouldnt think so and I certainly wouldnt be using a ground in another case on the other side of some connectors as a star ground for the amp
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Old 23rd May 2012, 01:02 PM   #14
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This need to be clarified a little. Did you mean to connect each analog PSU to each of two secondaries of transformer? And also connect secondaries at the center? Each secondary has 18V AC, wouldn't series give twise voltage at the same current? Or if I connect each psu at the separate secondary with secondaries connected, the voltage at each entrance of PSU bridge rectifier will be desired 18V AC? Sorry but I'm not strong in transformer theory.

Here is schematic picture as I understood all you said.

Click the image to open in full size.
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Old 23rd May 2012, 05:11 PM   #15
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That won't work.

If you look at the dual 18 V xfmr, the lines need to be connected as follows for both the PGA2320 and The Wire power supplies (which connect to the xfmr in parallel):
AC
GND
GND
AC

It's OK to connect the windings at the center tap; you can use that as a star ground.

To make that clear, each PSU needs both 18V~ secondaries.
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Old 23rd May 2012, 08:17 PM   #16
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Here is my second try at this, please help me and correct the scheme if you'll see mistakes.

Click the image to open in full size.
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Last edited by TiEx; 23rd May 2012 at 08:22 PM.
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Old 23rd May 2012, 08:41 PM   #17
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That's better.

Then you can connect DGND to the center tap (assuming it's not connected to AGND anywhere else), and you should be set.
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Old 23rd May 2012, 08:55 PM   #18
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I think digital part of PGA2320 and its MCU controller should be fine without any grounding (If I'm profoundly mistaken maybe then I need another transformer with dual secondaries, or center tap like 9V-0-9V). As I read elsewhere grounding is important for analog and bipolar PSU.

Anyhow, as long as center tap from dual secondaries is connected to analog PSU. And there is a recommendation in TexasInstruments datasheet for PGA2320.

And it clearly states:
Quote:
PRINTED CIRCUIT BOARD LAYOUT GUIDELINES
It is recommended that the ground planes for the digital
and analog sections of the printed circuit board (PCB) be
separate from one another

Last edited by TiEx; 23rd May 2012 at 08:58 PM.
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Old 23rd May 2012, 10:39 PM   #19
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Quote:
Originally Posted by TiEx View Post
There are some reasons to use NEMA box. Plastic is easy to work with and ground is not a problem as I am planning to do just as you suggested. Also thinking of connecting the transformer secondaries in center tap scheme for the analog supply. This way ground plane should be ok.

Click the image to open in full size.
This drawing has a typo error. The polarity dots and the terminal numbers are mixed-up.
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Old 24th May 2012, 03:01 AM   #20
qusp is offline qusp  Australia
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Default dual secondary for center tap

more like this mate. if dot means beginning of a winding, then dot = white wire on the dodgy pic I have made up. black from first to second is negative, green ground and red positive
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Last edited by qusp; 24th May 2012 at 03:05 AM.
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