Variations of DC Main Filter against buzzing Toroid Transformers - what is the right? - diyAudio
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Old 16th February 2010, 01:25 PM   #1
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Default Variations of DC Main Filter against buzzing Toroid Transformers - what is the right?

There are several versions of main DC Filter resp. DC blocker to avoid humming and buzzing, if there are DC components by the main voltage. In the PDFattachement I have filed several versions.

Here some URLs in this case:
dc filter
Christian's Homepage
L C Audio Technology / DC Filter
What Hi-Fi? Sound and Vision - Mains DC Blocking help
Thule Audio's Universal Inrush Current Limiter for their Amplifiers - very special? post #9

What is now the circuit with best reliability for such mains DC filter resp. mains DC blocker to block DC components from the otherwise singing and buzzing toroidal main transformer ?

I guess a corresponding number of parallel EPCOS foil's MKT's together with the suitable anti parallel connected diodes (possibly suitable anti parallel connected diode serial networks of two or three serial diodes)
Or an complete other solution that meets the same purpose is much
more better (e. g. a DC compensation network in parallel mode).

Here URLs regarded electrolytic caps:
Electrochemistry Encyclopedia -- Electrolytic capacitors
(ELECTROLYTIC CAPACITORS - basic description)

I note by the FTcap datasheets, that the max allowed voltage of reverse polarity of their electrolytics is always the same value of 2V,
independend of the forward voltage value - e. g.:
http://www.ftcap.de/downloads/elektr...2009/G2009.pdf
http://www.ftcap.de/downloads/elektr...009/GW2009.PDF
by some other brands I get only 1V.

With respect to this - what is the right version to get highest reliability - that is the question.
Attached Files
File Type: pdf Main DC Filter 10 variations.pdf (56.3 KB, 1287 views)

Last edited by tiefbassuebertr; 16th February 2010 at 01:28 PM.
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Old 16th February 2010, 01:41 PM   #2
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Example one should do the trick (there are several threads about that particular DC blocker here). No need for lots of components. Just a nice simple way to prevent DC
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Old 17th February 2010, 01:36 AM   #3
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Click the image to open in full size.

Only one bridge needed for amps less than 500W
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Old 17th February 2010, 09:21 AM   #4
AndrewT is offline AndrewT  Scotland
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Crown's two bridge rectifiers are to create the dual polarity power supply.
Bryston's two bridge rectifiers are for a completely different purpose.
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Old 17th February 2010, 11:43 AM   #5
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As we can see in the above Crown schematic, the two bridges are in parallel to increase the current capacity for their large amplifiers. Note 5 says only one bridge is used on the smaller models.

The left-hand bridge on the Bryston schematic is out-of-circuit under normal use. Current only flows when there is a bad ground loop, its function is to keep the 100R resistor from burning up (and you will hear a nasty buzz until you fix the ground loop). The right-hand bridge is the DC blocker.
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Old 17th February 2010, 05:52 PM   #6
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Quote:
Originally Posted by Jan Dupont View Post
Example one should do the trick (there are several threads about that particular DC blocker here). No need for lots of components. Just a nice simple way to prevent DC
Yes, but none of these threads answer my question from post # 1 (except that one filed about other headlines and therefore I don't find).

And what is the better and at the same time easy i. e. passive way in your opinion to remove DC components (except active power conditioner respectively uninterruptible power supply/UPS)?

Perhaps an isolating transformer?
Or an parallel DC compensation like this one of the follow URLs?
http://www.horch-gmbh.de/Produkte/Line%20Silencer.pdf
Horch Elektroakustik - open-end-music-professional (post #9)
Unfortunately, less than one weblink in English
The related circuit I want to know.

Last edited by tiefbassuebertr; 17th February 2010 at 05:54 PM.
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Old 17th February 2010, 09:00 PM   #7
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The easiest way is to follow the example from Crown, one component, period.
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Old 17th February 2010, 09:16 PM   #8
mlloyd1 is online now mlloyd1  United States
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given the lack of formal data, we can't really comment on what is the most reliable approach
however, anecdotally speaking (or if you held a gun to my head to make me choose ), i would probably vote for bryston's approach:
1. 20 year product warranty
2. products known to stand up to use in tough environments
3. bryston is still in business. in other words, items 1 and 2 have not been problematic enough to shut them down or even give their products a bad reputation

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Old 18th February 2010, 10:42 AM   #9
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Quote:
Originally Posted by mlloyd1 View Post
given the lack of formal data, we can't really comment on what is the most reliable approach
however, anecdotally speaking (or if you held a gun to my head to make me choose ), i would probably vote for bryston's approach:
1. 20 year product warranty
2. products known to stand up to use in tough environments
3. bryston is still in business. in other words, items 1 and 2 have not been problematic enough to shut them down or even give their products a bad reputation
mlloyd1
Yes, that is the only way that I also go. However - nevertheless it would be interesting to know who invented this topology, and used it at first.
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Old 18th February 2010, 11:35 AM   #10
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The Crown Studio Reference 1 schematic is dated 1994, the Bryston 4BST is the first example I can find in the Bryston line is dated 1996.

The difference between the two is the pair of electrolytic caps in the Bryston, Crown doesn't seem to feel they are needed.

If you really want to know, build it like the Crown, and then try adding the Bryston caps.
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