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kyrochan 23rd March 2005 10:51 PM

PSU transformer question
If I connect in parallel (matching together the 0V and the 24V wires) the secondaries of two identical trasformers rated for 24V/96VA should I obtain a 192 VA /24V trasformer?

audiofan 24th March 2005 12:11 AM

yes you should, but remember that the primary and the secondary must be in phase, to make test always use a ligtbulb in series with the mains for your test if connection is ok the lightbulb will not ligt up if your connection is out of phase (reversed ) the light will go bright

kyrochan 24th March 2005 12:45 AM

So, you say that it's possible that the colours of the primaries on the two transformer could be inverted?!
(my transformers is single primary / single secondary)
and so could happend that in the moment I matched the wires of the secoundaries (live with live and ground with ground) they could go in short?
Ehi, this is extremely dangerous!
What kind of mad engineer can make a mistake like this? !

Giaime 24th March 2005 07:58 AM

Ciao! Yes it can happen. But it is a rare event. Try the lightbulb trick in series with the primary leads. It senses the short and protect the transformers in case of serious trouble. In general if the 2 transformers are identical, just connect togheter the wires of the same color...

But why are you doing this? Get a cheap 225VA toroid and you'll thank yourself later... (I assume you are talking about EI transformers)

kyrochan 24th March 2005 10:13 AM

I've bought these 4 trasformers for just 15, they are preatty heavy and well made, I bought 4 trasformers to create a two-rails psu like ones suggested by dejan Vaselinovich in his tnt articules...but since I search a pure class A amp, I 've decided to built a Zen amp (single ended) I think that I can't use a two rail psu in a single ended amp so I've decided to connct them parallel to got a nice psu for a 15-20W final mono.
If you could suggest a way to implement a two rail psu in S.E. amp make me know.

K-amps 24th March 2005 11:53 AM


Unless the trafo's are made to very high tolerances, they may not match. You need to connect all wires in paralell, then open one connection at one end of the secondaries and measure the voltage difference. It should be less than 0.05v (5mV) anything more and your transformer will drive the other and cook it.... use a 20-40 watt bulb to check.

SkinnyBoy 24th March 2005 11:56 AM

if we're talking seperate transformers, then I would parallel them after the bridge rectifiers :) :smash:

K-amps 24th March 2005 12:22 PM

If they are not matched to within 0.05v or so, then yes the next step would be to join after the Bridges.... but then you need an extra bridge.

kyrochan 24th March 2005 12:47 PM

2 Attachment(s)
Mmmmh, how did you think about this way to use the rectifiers???

K-amps 24th March 2005 12:53 PM

That gives you double the voltage and single supply.... is that what you wanted?

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