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endia 8th January 2005 06:20 PM

transformer secondaries question
 
hello all,
this is my first post on diyaudio :)

i bought a 225VA 18-0-18 toroidal transformer from a local dealer. actually i asked dual secondaries but they hasn't one and seller pointed out that center wire is actually two wires which are twisted together. he said you can easily seperate them and then you have got dual secondaries. is there any risk if i do this? i'll use it for building a gc.

thanks.

Stocker 8th January 2005 07:13 PM

6 of one, 1/2dz. of the other. Don't bother separating them unless you just feel like it, if you plan to run a +/- supply to the chip anyhow.

endia 9th January 2005 12:42 AM

Stocker, thanks for the quick replay.
i just want to use one rectifier bridge for each +,- rails instead of one for both rails, doesn't it matter?

wxn 9th January 2005 08:28 AM

For two rectifiers you must have two separate secondaries, not center-tapped. gl

endia 9th January 2005 12:21 PM

well, is this the only way for wiring a center-tapped transformer?

http://img.photobucket.com/albums/v9...ther/ct_01.jpg

if so, i'm a bit confused. where to go PG+ and PG- holes on the amplifier board? should i connect both PG+/- holes to the PG? or may i wire them like this? thanks.

http://img.photobucket.com/albums/v9...ther/ct_02.jpg

Sherman 9th January 2005 03:32 PM

2 Attachment(s)
Quote:

Originally posted by endia
well, is this the only way for wiring a center-tapped transformer?

http://img.photobucket.com/albums/v9...ther/ct_01.jpg

if so, i'm a bit confused. where to go PG+ and PG- holes on the amplifier board? should i connect both PG+/- holes to the PG? or may i wire them like this? thanks.

http://img.photobucket.com/albums/v9...ther/ct_02.jpg

NO! I have built several GC power supplies using center tapped transformers. Let's call the three secondary leads from the transformer AC1, CT and AC2. Let's call the four connections on the dual bridge power supply AC1H, AC1N, AC2H and AC2N.

I wire AC1 to the AC1H connection in the PS. Then wire the CT to both AC1N and AC2H. Wire the AC2 tap from the transformer to AC2N.

Doing it that way you can use a CT transformer in a dual bridge power supply. The image shows an example with the BrianGT boards.

richie00boy 9th January 2005 03:44 PM

You can wire it like that, but you are wasting half of each bridge and gain none of the advantages of using separate bridges.

SM7UYJ 9th January 2005 04:33 PM

Hi,
Have not found a clear answer to why two bridges produce a better result. With center tap you still get full wave rectification(sorry for crappy spelling).
Sure half current trough the diodes, but just use bigger ones! What are the advatages of using two bridges? Can some one please explain!

wxn 9th January 2005 05:00 PM

SM7UYJ:
http://www.tnt-audio.com/clinica/ssps2_e.html

SM7UYJ 9th January 2005 06:07 PM

Hi wxn,
Have actualy read this information before, but I'ts still not clear!
Yes, you get half the current in the diodes but this is only a problem if you have ones not capable of handeling the current = use bigger ones!:confused:
Crossover! From what ! Is'nt the circuit made to produce DC for your amp - not the other way arround!? Is'nt this then a 'work arround' for an other problem in the design used?
Larger groundplane! Uhhh...center tap to ground -can it get bigger/shorter/easier!?
I'm a newbee to the audio circuits so excuse my stupidity, but I'm perhaps coloured from building PSUs and amps for hamradio (RF)where demands on DC-ripple and voltage stability under load are much higher and when choosing a trannie - centertapped are prefered by me and many.
Can some one explain ( in simple words;) ) why use two bridges!?

/RC


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