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Old 21st August 2008, 01:14 PM   #1
gbolly is offline gbolly  United Kingdom
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Default two single secondaries, two rectifier boards lm4780 kit

hello guys,

i recently made a mistake and bought a pair of 300va 23v toroid transformers on ebay without reading the description properly only to find out that they each have single secondaries.

i know thus far that you can wire both transformers together by connecting together the two primarys and then have two seperate secondaries to work with a single peter daniel rectifier board.

my questions are,
could i connect a second rectifier board in parallel to the first so i can get to connect a second amp board (im aware i could get hums or buzzing from ground loop issues)?

would having seperate star grounds for each of the rectifier board/amp board combos make any potential ground loops go away or at least be minimized

i :

am using the peter daniel lm4780 kit

plan on actively biamping a pair of mordaunt short ms908 floorstanders (i doubt 1 amp board will be enough for the two, want to assign one amp board to each speaker)

not fussed too much about dual mono configuration for now, just want to maximize the two traffo's.

thanks in advance
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Old 21st August 2008, 01:28 PM   #2
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Default Re: two single secondaries, two rectifier boards lm4780 kit

Quote:
Originally posted by gbolly
my questions are,
could i connect a second rectifier board in parallel to the first so i can get to connect a second amp board (im aware i could get hums or buzzing from ground loop issues)?
You could, but you only need to do that, if the current rating of a single board is too low for two amps. If it isn't, so you can run your two amps from one rectifier board.

Quote:
Originally posted by gbolly
would having seperate star grounds for each of the rectifier board/amp board combos make any potential ground loops go away or at least be minimized
Probably not.
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Old 21st August 2008, 06:00 PM   #3
gbolly is offline gbolly  United Kingdom
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thanks
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Old 22nd August 2008, 01:37 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
300VA 23Vac gives 13amps from that single winding.
It is very unlikely that a single wire is used for 13A. Much more likely is that it is bi-fillar or tri-fillar wound. 13A requires somewhere around 2.2 to 2.3mm diameter copper single core, or two cores of 1.6mm diameter, or three cores of 1.3mm diameter.

Open up the outer insulation and look at the connection where the winding meets the lead out.

If it's bi-fillar then add on separate lead outs for each wire in the secondary.

If it's tri-fillar add on a complete 23Vac winding and make a four secondary transformer. This allows complete isolation for two channels.
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Old 22nd August 2008, 08:11 PM   #5
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Quote:
Originally posted by AndrewT
If it's bi-fillar then add on separate lead outs for each wire in the secondary.
Is this also the best way for me to wire a single 300VA 18V+18V to a pair of rectifier boards?
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Old 23rd August 2008, 07:59 AM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Redshift187
Is this also the best way for me to wire a single 300VA 18V+18V to a pair of rectifier boards?
no, too much work when the lead outs are already there.
However, if the leadouts are solid core then it is worth the effort to open up and replace these with flexible leadouts to permit experimentation of orientation of the transformer.
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