two seperate single secondary toroids = combined center tapped transformer?? - diyAudio
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Old 5th November 2008, 12:20 PM   #1
gbolly is offline gbolly  United Kingdom
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Default two seperate single secondary toroids = combined center tapped transformer??

hello again,
i recently came across a pair of identical 300va 240v/23v single secondary toroidal transformers which i am going to use for my gainclone.

originally, i intended to use both transformers to wire a peter daniel (audiosector) power supply board such that one transformer will go to ac1 and ac2 connections on the board(one half of the dual power supply)

while the second transformer will go to ac3 to ac4 connections (seconds half).the primaries will be paralleled to produce 240v

in essence im using the two transformers as a single giant 600va dual secondary transformer set.

this whole system of tranformers including the power supply board will be enclosed in a seperate case and connected to the amplifier enclosure with a custom made umbilical using 4 pole speakon connectors and sockets and high current (>30A each) wire .

the four cables will carry the power from the transformers to the amp enclosure.

the amp will be a single lm4780 board running in stereo mode with the hope of incorporating a second amp board later on.

***********my dilenma follows***************
can i wire the two transformers as 23v-0v-23v (connecting the secondaries in series) leaving the 240v primaries in parallel?
this way, i can transfer power to the amp enclosure using only 3 poles of the umbilical and use the last pole for the earth/ground network.
this is very desirable for aesthetics/ safety reasons......... phew


can anyboy help me please?

p.s ive altered the power supply board to reflect the center tapped transformer config.
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Old 5th November 2008, 12:24 PM   #2
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I would use the dual secondary configuration of the board, and tie the PG+ and PG- together with the safety earth (that's how I wired my LM4780 amp, although I was using one toroid).
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Old 5th November 2008, 12:41 PM   #3
AndrewT is online now AndrewT  Scotland
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300VA should easily manage 60+60W of output.
120 to 240VA is a reasonable range of transformer power for a 60W stereo amplifier. 300VA may give a slight performance gain.
I would save the second transformer for another pair of amplifiers.
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Old 5th November 2008, 01:04 PM   #4
Did it Himself
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He can't Andrew as each transformer only has single 23V secondary.

What gbolly wants to do is fine if a little overkill on VA rating.
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Old 5th November 2008, 02:09 PM   #5
gbolly is offline gbolly  United Kingdom
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thanks so far for your responses

the real deciding factor is the umbilical (4 pole speakon plugs and sockets+hc cables x4).

i want to keep all necessary cabling within the umbilical hence the reason why i want to wire the transformers for +v,-v, pg, earth/ground net.

p.s ive already fashioned a disconnecting network to lift the audiuo ground from the earth (10ohm 7 watt wirewound in series with 100nf cap rated at 400v, 35a rect bridge)
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Old 5th November 2008, 03:56 PM   #6
AndrewT is online now AndrewT  Scotland
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Default Re: two seperate single secondary toroids = combined center tapped transformer??

Quote:
Originally posted by gbolly
300va 240v/23v single secondary toroidal transformers
I still can't read.
But, that is a 13A transformer.
The secondary will not be wound with a single core 13A winding.
Have you tried to look through the insulation to see if it has a bi-fillar or tri-fillar wound secondary?
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