Where is it best to send the rectified DC - diyAudio
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Old 25th September 2011, 07:35 AM   #1
robmil is offline robmil  United Kingdom
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Default Where is it best to send the rectified DC

hi all

I have been reading stuff of this site and it has confused me a bit.

I have built a few power supplies in the past and always taken the rectified DC from my rectifiers to the filter caps ...

In the image attached the chap takes the rectified DC and places it after the filter caps. I've attached an URL to his site also.

thanks for the help.

High End Audio - Preamplifier model 4
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Old 25th September 2011, 07:37 AM   #2
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Quote:
Originally Posted by robmil View Post
hi all

I have been reading stuff of this site and it has confused me a bit.

I have built a few power supplies in the past and always taken the rectified DC from my rectifiers to the filter caps ...

In the image attached the chap takes the rectified DC and places it after the filter caps. I've attached an URL to his site also.

thanks for the help.

High End Audio - Preamplifier model 4
The connection is the same whether you draw it on the right or the left side. It's the connection that counts; I guess he just did it to keep the drawing compact.
If you flip it around it looks different again, but still is electrically the same.

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Old 25th September 2011, 08:20 AM   #3
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by robmil View Post
hi all

I have been reading stuff of this site and it has confused me a bit.

I have built a few power supplies in the past and always taken the rectified DC from my rectifiers to the filter caps ...

In the image attached the chap takes the rectified DC and places it after the filter caps. I've attached an URL to his site also.

thanks for the help.

High End Audio - Preamplifier model 4
BTW, a transformer is pretty worthless as a filter choke: the iron will begin to saturate as soon as the DC current reaches several tens of mA, with the associated non-linearity and and loss of effectiveness.
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Old 25th September 2011, 08:45 AM   #4
robmil is offline robmil  United Kingdom
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Hi

On his site he goes on to say the connection point DOES make a difference. He goes on to say that the noise levels are lower if you enter after the filter caps as in the picture and this is to do with the heavy charging currents.
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Old 25th September 2011, 11:33 AM   #5
AndrewT is offline AndrewT  Scotland
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It looks like a CLC filter.
The L taps in after the first C.
I doubt that tapping a supply direct to the L output rather than the second C output will improve the quality of the DC.
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Old 25th September 2011, 11:34 AM   #6
robmil is offline robmil  United Kingdom
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thanks Andrew
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Old 25th September 2011, 11:53 AM   #7
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by robmil View Post
Hi

On his site he goes on to say the connection point DOES make a difference. He goes on to say that the noise levels are lower if you enter after the filter caps as in the picture and this is to do with the heavy charging currents.
Had a look at the site... he's very enthusiastic about it all

I can't really grasp his logic on the PSU...

Trying to imagine what he's thinking. It's not like an amplifier output where the output (and feedback takeoff) should be run off a small spur. That is done to avoid the problem of small but not negligable resistances of print/solder/wire etc.

Hazy thinking without sitting down and drawing it out suggests that three 100uf caps esentially "share" the total ripple current. So the current in each "wire" to each cap has 1/3rd of the total ripple current. But each cap still "sees" the total combined ripple voltage that is on the main connection back to the rectifiers...

If you assume the conductors/wire/print have perfect zero ohm properties then it does not matter where the connection is made. If you accept they have small values of resistance then I thing the difference in e.s.r. of the caps would become dominant in the distribution of charging currents but would there be a point in all the connections/wiring that a constant current load would "see" a slightly (and it would be microscopic) lower level of disturbance... I not so sure.

Over to somebody else

All I would say is that careful and correct wiring is really the big big thing to get right in any design. You have to treat each each conductor as a resistance and make sure that whatever develops across it can not alter the signal in any way.
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Old 25th September 2011, 01:27 PM   #8
DF96 is offline DF96  England
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He should attach the incoming DC + and - from the rectifier etc to the left-hand end of the caps, and take a clean outgoing DC (and ground) from the right-hand end of the caps. So the only thing he has got right there is the position of the ground at the output. Unfortunately he then spoils it by injecting charging pulses into it!

I can't be bothered to read his site, but if this diagram is typical then I suspect that he doesn't really know what he is doing. All that bypassing is a little silly, especially with such a poor wiring/grounding arrangement. As Elvee says, a mains transformer will make a rather poor choke - maybe it is an attempt at a swinging choke?

"High end" Really?
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Old 26th September 2011, 12:56 AM   #9
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From the same site/page:

highdefalim.gif

So much wrong with that logic.
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Old 26th September 2011, 01:36 AM   #10
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These guys.....Although they don't buy in to the zillion dollar cabling scam , they do seem obsessed with the whole "Vibration suppression is paramount to good sound"......camp.
Sighing & shaking head.

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