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Old 20th February 2004, 09:58 AM   #1
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Question Are dual rectifier bridges useful?

Can someone please explain to me how a single diode bridge feeding from a center tapped transformer could somehow result in 50 Hz ripple?

I have been seeing this statement repeated ever so often, but has anyone actually bothered to simulate this in PSPICE? Or even better, actually put a 'scope across the capacitors?

It does make some sense to use separate bridges if the windings supply voltages that differ substantially, as could reasonably be the case if you're using two separate transformers, but from a single? I doubt it...

Having separate bridges for each channel is probably a good idea, though.

Rune
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Old 20th February 2004, 10:03 AM   #2
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You will get 100 Hz.

Why don't you download LTSpice (freeware) and test for yourself? A good excersize (spelling?) if you haven't fooled around with simulation before.

Your first question: Two bridges and two separate windings creates a little less harmonics(= heat) but for normal duty or light duty I think this is "hugget som stucket"(*).

Anybody who has compared one and two bridges and the differensies in harmonics and heat?

*) Mr D what does this mean in english?
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Old 20th February 2004, 10:22 AM   #3
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Two bridges in summary heat more than only one, 'cos in this case you have two diodes in series ( one against rail, one against ground ).
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Old 20th February 2004, 10:37 AM   #4
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I meant in the transformer.... but of course you will get extra losses in the diodes.
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Old 20th February 2004, 04:24 PM   #5
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Well, I knew that, but I see a lot of dual bridge setups in the chip amp forum, and nobody seems to question the benefit of that. I was hoping to open some eyes.

But yes, I sure need excercise in Spice simulation. So much to do, so little time. I'm trying to learn some 3D modelling in 3DS Max, but the dang program hangs my 'puter real good. Maybe I should try excorcising instead?

Jämna plågor, med andra ord...

Rune
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Old 20th February 2004, 04:29 PM   #6
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maybe they were using low voltage diodes?

Other than that, i see no reason to go with a dual bridge set-up. But that's a place where Egyptian maple boxes make audioable difference so I couldn't be too sure.
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Old 20th February 2004, 04:46 PM   #7
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Rune, since the topic has been discussed in some 50 threads already to a point where most people are sick of it I think you will get fairly little attention.
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Old 20th February 2004, 07:15 PM   #8
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Dual bridges allow that the power transformer does not have to be connected to the ground to create a center tap.
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Old 20th February 2004, 07:25 PM   #9
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Default Re: Are dual rectifier bridges useful?

Quote:
Originally posted by runebivrin
Can someone please explain to me how a single diode bridge feeding from a center tapped transformer could somehow result in 50 Hz ripple?

I have been seeing this statement repeated ever so often, but has anyone actually bothered to simulate this in PSPICE? Or even better, actually put a 'scope across the capacitors?

It does make some sense to use separate bridges if the windings supply voltages that differ substantially, as could reasonably be the case if you're using two separate transformers, but from a single? I doubt it...

Having separate bridges for each channel is probably a good idea, though.

Rune
Actually it's good to see posts like this as it makes one think more about the design choices. I don't care at all what ripple I'm getting by using one or two bridges, but I'm quite interested if there is a difference in sound when using both combinations.

I once compared one bridge against two separate bridges (with Schottky rectifiers) and I was under the impression that two separate bridges sounded much better. But again, it seems that 47Labs are using only one bridge and I've seen claims about sound superiority with one bridge only. I will be testinfg that again over the weekend.
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Old 20th February 2004, 07:51 PM   #10
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UrSv:
Judging from what I'm seeing as proposed designs, I'm not the only one to have missed those threads, and they must be at least nearly a year old, so maybe there's some point in raising the issue for the 51:st time.

John:
I see what you mean, but I'm afraid I'm at a loss as to the benefits of not having the transformer windings connected directly to ground. Is it just an observation of a difference, or something that actually matter under certain conditions?

Peter:
I understand you're a fly by ear kind of guy, and I definitely respect the level of introspection you must suffer/enjoy to hear the differences. I'm more of a "If I sing along, it probaby sounds OK" type.

All:
I'm pretty much in the process of trying to discover how much electronics I remember after a 20 year hiatus. Part of that is challenging what I see and trying to understand the reasoning behind various statements. If they sound off the wall, maybe it's because I'm hanging from the ceiling. I've been wrong before (once in '74, if I remember correctly), but I do consider myself reasonably clever.

Rune
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