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Old 30th July 2012, 09:43 PM   #21
DF96 is online now DF96  England
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See this, especially Figure 2. Note that the transformer CT goes to one end of the caps ground connection, and the amp/speaker return/chassis grounds all go to the other end.
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Old 30th July 2012, 09:48 PM   #22
jcx is offline jcx  United States
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schematics can imply conductor order too - that fig 1 schemtic drawing is bad practice if you want the physical wiring order shown in fig 2
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Old 30th July 2012, 09:54 PM   #23
DF96 is online now DF96  England
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Yes, he sort of says that but I would prefer to see a redrawn fig 1 to emphasis the point. Maybe we could say that fig 1 is how many people draw circuits, and sadly how some people wire circuits.
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Old 31st July 2012, 05:49 AM   #24
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by DF96 View Post
See this, especially Figure 2. Note that the transformer CT goes to one end of the caps ground connection, and the amp/speaker return/chassis grounds all go to the other end.
Funny, the schematical representation in fig 3.2-4 and the connection in between the caps in the drawing look the same to me: a star. If this is a copper rod, then the resistance from end to end is very very small (my guess < 0.5-1 milliOhm) and cannot be considered a bussed ground. If these are terminals that are screwed down to it, the contact resistances might be higher than the resistance of the rod.

What the author meant with "bussed ground" is more like long traces between the several different caps in the PSU filter, resembling e.g. the long power supply strips of a breadboard. This is most likely what OP is suffering from and hence my request to retry the PSU built according to fig 3.2-4.
To my mind we were talking about the same thing, but calling it different names.

I'm guessing the drawing is a hardwired setup, but if you were to place the caps on a pcb, a large copper area in the same place between the caps would act the same.
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Old 31st July 2012, 09:54 AM   #25
DF96 is online now DF96  England
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Quote:
Originally Posted by jitter
Funny, the schematical representation in fig 3.2-4 and the connection in between the caps in the drawing look the same to me: a star.
OK, so you don't understand the basics of grounding. Two rules: every connection has resistance so will drop some voltage so make sure this happens in the right place; every grounded point must have one and only one connection to every other grounded point so no loops.

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If this is a copper rod, then the resistance from end to end is very very small (my guess < 0.5-1 milliOhm) and cannot be considered a bussed ground.
It is a bus because it is not of zero size and zero resistance. The resistance is small, but 1 milliohm is a lot if you have, say, 10A peak charging pulses. In fact, every star is really a small bus. The trick with grounding is to ensure that these 10mV (or whatever) signals appear where they can do no harm. His wiring is correct: the dirty stuff is at the CT end and then he grounds the clean end at the other end of the copper.
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Old 31st July 2012, 01:03 PM   #26
wicked1 is offline wicked1  United States
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Thanks everyone, I didn't have time last night, but will definitely rebuild the supply tonight w/ careful attention to grounding. This has all been very informative. I know everything flows down the path of least resistance, but never thought about how literal that is in practice.
I'm actually starting to wonder how my couple of point to point amps I built from scratch are successful! I guess I did build those w/ careful attention to grounding, unlike this breadboard power supply.
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Old 1st August 2012, 01:02 AM   #27
wicked1 is offline wicked1  United States
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Alright, I rebuilt it. It's quiet. It's still on breadboard, so I couldn't exactly do a star, but did bus.. grounded everything along the conductor going down one edge of the board. CT in the first hole, cap in the 2nd, regulator grounds in the next few, and finally the connection to the synth.

Now I've discovered a problem w/ my home electric. When the AC goes on the power drops about 10v which doesn't leave enough for my 12v regulator! I should have gotten a 2x15v transformer, rather than the 2x12 I've got. (Or 200 amp service to my house )

Thanks DF96, and everyone else too.

Last edited by wicked1; 1st August 2012 at 01:11 AM.
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Old 1st August 2012, 04:20 PM   #28
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by wicked1 View Post
Alright, I rebuilt it. It's quiet. It's still on breadboard, so I couldn't exactly do a star, but did bus.. grounded everything along the conductor going down one edge of the board. CT in the first hole, cap in the 2nd, regulator grounds in the next few, and finally the connection to the synth.
Good to know! Does it make any difference if you unplug the CT and plug it in the hole next to the synth-connection?

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Now I've discovered a problem w/ my home electric. When the AC goes on the power drops about 10v which doesn't leave enough for my 12v regulator! I should have gotten a 2x15v transformer, rather than the 2x12 I've got. (Or 200 amp service to my house )
If you use Schottky diodes in the rectifier instead of normal silicon diodes, you might get away with using the 12 V transformer. These diodes have a lower forward voltage drop that might just leave you enough juice to keep the regulators happy.
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Old 1st August 2012, 05:00 PM   #29
jitter is offline jitter  Netherlands
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Originally Posted by DF96 View Post
OK, so you don't understand the basics of grounding. Two rules: every connection has resistance so will drop some voltage so make sure this happens in the right place; every grounded point must have one and only one connection to every other grounded point so no loops.


It is a bus because it is not of zero size and zero resistance. The resistance is small, but 1 milliohm is a lot if you have, say, 10A peak charging pulses. In fact, every star is really a small bus. The trick with grounding is to ensure that these 10mV (or whatever) signals appear where they can do no harm. His wiring is correct: the dirty stuff is at the CT end and then he grounds the clean end at the other end of the copper.
Thanks for clearing things up.
I had a look at the layout of the PSU board of one of our customers and noticed a similar setup as advised by you. The CTs are connected to one side of the board (along with the AC voltages), more or less in the middle are the caps and on the other end the power supply common leaves the pcb (along with the DC voltages). Grounding is taken care of by one big groundplane on the bottom of the board.
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Old 1st August 2012, 09:04 PM   #30
DF96 is online now DF96  England
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Yes, that is the way to do it. If you try to use a star for PSU grounding it is harder to ensure that the connections occur in the right order. Some people get away with it either through skill or luck; for the rest of us a short bus is the best option.
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