transformer secondaries question

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

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.

ct_02.jpg
 
endia said:
well, is this the only way for wiring a center-tapped transformer?

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.

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.
 

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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!
 
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
 
Sherman said:

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.

Sherman, thanks to schematic, i'll do it that way but i have a question;
AC1 and AC2 (from the transformer) are our hot wires, aren't they? why we don't wire AC1 to AC1H, AC2 to AC2H and then CT to both AC1N and AC2N?
 
If you use two bridges and have twin secondaries, you load the transformer better so can get a little more current out of it for the same temperature.

Also, it's better from a grounding perspective as when the top half circulates current it does not travel in the same ground loop as the bottom half, and the star ground really is only at the centre point of the smoothing caps. With a single bridge or centre tapped transformer, the star point is shared between the caps and the tap, so the length of this connection is important/influential.
 
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