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Old 4th July 2007, 03:10 AM   #21
Archwn is offline Archwn  United Kingdom
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Hi Andrew.

You are right that i thought that's the one.

dig more deeply and found the leak. Carlos F M has another one with 2 lm338 - this should be the one we're talking about.

I'm not so sure about this implimentation but from my logic it should work. (i m a newbie in electronics by the way)

please comment.

cheers,

AK
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Old 4th July 2007, 04:01 AM   #22
BWRX is offline BWRX  United States
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If you are going to use two positive regulators a dual secondary transformer is necessary, and that schematic you posted is incorrect. You cannot use a center tapped secondary with two positive regulators. That schematic shows two positive regulators but has the ground connected at the incorrect place. With a dual seondary transformer, the ground becomes the connection between the ground of the positive rail regulator and the output of the negative rail regulator.
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Old 4th July 2007, 09:04 AM   #23
AndrewT is offline AndrewT  Scotland
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Hi,
Bwrx is correct, you need a dual secondary for the two rectifier solution to work. That dual rectifier is necessary for the dual positive regulators.
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Old 5th July 2007, 03:17 AM   #24
Archwn is offline Archwn  United Kingdom
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Hi BWRX, Andrew,

Thanks for your comment.

Are there any other reasons rather than 5A neg. reg. is not readily available to use this 2 pos. reg.? I mean any other benefits using 2 pos. reg. and 2 secondaries rather than 1 pos.
and 1 neg. regulator?

I have seen people using 2 secondaries 8 reg. diodes rather than center tapped and 4 reg. diodes on the 'unreg' PS ones. does this based on the same benefits?

Cheers,

AK
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Old 5th July 2007, 07:36 AM   #25
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Archwn
any other benefits using 2 pos. reg. and 2 secondaries rather than 1 pos. and 1 neg. regulator?
As far a I know they perform equally well. But take care with conventional pos +neg with an apparently common power ground running through the combination. It must not.
Quote:
Originally posted by Archwn

I have seen people using 2 secondaries 8 reg. diodes rather than center tapped and 4 reg. diodes on the 'unreg' PS ones. does this based on the same benefits?
completely different requirement.
The dual bridge is claimed to offer lower hum on the power ground. I have not been able to measure any improvement.
The dual bridge does waste twice as much voltage and twice as much power. I don't think it helps (a change in my opinion) in reducing diode temperatures. (I have just changed my Krell Klone from dual bridge to paralleled single bridge to reduce the diode temperatures, not to save costs nor to reduce performance).
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Old 5th July 2007, 07:15 PM   #26
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Quote:
Originally posted by Archwn
(snip)
Are there any other reasons rather than 5A neg. reg. is not readily available to use this 2 pos. reg.? I mean any other benefits using 2 pos. reg. and 2 secondaries rather than 1 pos.
and 1 neg. regulator?
(snip)
AK
In the May 2007 issue of audioXpress magazine, Walt Jung wrote in his article about another subject:
"... it is actually better performance-wise to use a pair of LM317s ... than it would be to use an LM317 and a LM337"

The reason being that the LM317 has better frequency response (AC rejection).
He also suggested not using low dropout regulators. Because of trade-offs in frequency responseOriginally posted by Archwn
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Old 6th July 2007, 05:10 AM   #27
Archwn is offline Archwn  United Kingdom
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Hi Andrew,

Thanks for your comment. So you're saying that using 1 pos. reg. and one neg. reg. with a common ground is not so good? or i got you wrong?

And the claim from 8 diodes reducing hum also found not to be true by yourself?

Hi Kevin,

Thanks for your comment. Sounds like a good go as I also have plan to go on regulated PS on my 3875(2xLM338 or LT1085).

Cheers guys,

AK
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Old 6th July 2007, 08:26 AM   #28
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No Andrew is saying that when you daisy chain grounds you get problems.
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Old 6th July 2007, 09:57 AM   #29
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Archwn
So you're saying that using 1 pos. reg. and one neg. reg. with a common ground is not so good? or i got you wrong?
no, I said
Quote:
As far a I know they perform equally well. But take care with conventional pos +neg with an apparently common power ground running through the combination. It must not.
it's the way the ground is run that matters. Most schematics adopt the chained or series string that is common in simulators and schematic software but both these assume perfect connections with no resistance and no inductance. The real circuit must not connect the smoothing cap zero volt line so that any load currents pass along wires carrying sensing signals for the regulators. The smoothing ground must go to the load and the sensing ground must go to the load.

Quote:
Originally posted by Archwn

And the claim from 8 diodes reducing hum also found not to be true by yourself?
no, I said
Quote:
The dual bridge is claimed to offer lower hum on the power ground. I have not been able to measure any improvement.
That may be a limitation of my measuring technique.
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