Dual transformer polarity/wiring

[Zero Cool]

I need to replace the transformer in a device and i am wondering about the best wire to wire two transformers for lowest noise.

Both transformers are the same brand model, and both have a single secondary winding. I need to wire the transformers together to develop a center tap.

Is is best to wire the transformers to that the Primaries are in parrallel 1 to 1 and 2 to 2 and then wire the secondaries in series. 1-2+1-2

or would it be better to wire the primaries with opposite polarity and then wire the secondaries to match?

1 to 2 and 2 to 1 on the primary side. then wire 1-2+2-1 on the seconday side?

Which way would be the lowest noise??


Zc

 

[BWRX]

It's probably best to just wire the primaries in parallel and the secondaries in series.

 

[KBK]

See if you can place the two transformers so that their fields overlay or overlap, so they are in the same magnetic field (observing polarity). This will work best. It can be done, just be careful. There was a thread on that recently. Heat and noise will be the result if done wrong (incorrect orientation), you will be aware of this immediately. In seconds.

 

[AndrewT]

Hi,
if you put the primary and the secondary connections through a terminal strip you will be able to change between the two options and listen for any changes.

Remember that light bulb before you switch on.

 

[XEAGLEKEEPER]

I would think primaries in parallel(in phase) secondaries in series.
http://www.sound.westhost.com/xfmr2.htm#8.series-parallel
READ THIS !!!!

 

[AndrewT]

Hi Eagle,
that does not help us.
He is asking what is better. To connect the two transformer primaries out of phase with the secondaries also wired out of phase to give the correct output
or
wire the primaries (two transformers) in phase and wire the secondaries in phase to achieve correct output.

Which sounds better?

 

[AMV8]

Hi

I have tried both ways in the past. Wiring the primaries in parallel and the secondaries in series worked. Wiring your second option did not produce good results.
I rang the transformer manufacturer - I think it was Avel Lindberg - it was I just checked - they said only use your initial suggestion as the other would may/would cause heating of the transformer. I think I did detect heating in mine but I blew a fuse in the transformer at that point ( I connected the wrong primary ) and never tried anything else as I already had a working system.

It is currently being used on an Aleph amp delivering 2 amps at 28v from a 130va transformer. It seems happy and quiet.

Don

 

[Zero Cool]

Well I have tried both ways and in this particular device i can detect no difference in sound quality of transformer temp.

I think that because the transformers are about 1" apart that there isnt sufficient magnetic coupling to cause heating.

This is a pro audio EQ and maybe this circuit just doesnt let me hear the differences well enough. A-B'ing the wiring seems to make no audible difference in noise, or sound quality. I think thta is it s poor circuit to begin with and any differences are masked by the poor circuit.

My thoughts were that if the primaries were wired out of phase then any incoming noise would be canceled. Power line noise rejection to me is most important as this will be used in many places with bad power.


Zc

 

[AndrewT]

Hi,

if the primaries were wired out of phase then any incoming noise would be canceled.

I don't think so.

 

[XEAGLEKEEPER]

if the primaries were wired out of phase then any incoming noise would be canceled.
NOT!!
Two transformers---primaries paralleled(in phase)--secondaries in series(in phase) 1---2+1---2

 

[soongsc]

I think connecting two transformers together is not a good idea since the phase relationship between the primary and secondary might not be exactly the same. I would connect these through two rectifiers first and then pull the DC together.

 

[AndrewT]

Hi Soon,
I suspect even your third alternative will similarly make no difference to the sound output, other than the loss of that extra 1.4volts will have on earlier clipping.

 

[soongsc]

Hi Soon,
I suspect even your third alternative will similarly make no difference to the sound output, other than the loss of that extra 1.4volts will have on earlier clipping.

I'm not sure where that 1.4Volts comes from. But I once used a transformer that had two 25V outputs rather than centertapped, connecting two in series created a little 60Hz little signal (little worm between flats that occur at around 60Hz) in the ground loop that could never be removed. Perhaps there is a different explanation?

 

[AndrewT]

Hi,
two rectifiers loses 2.8v whereas one rectifier loses 1.4v. I think you saw that.

Bad grounding caused the buzz, not the change to/from single rectifier.

 

[soongsc]

Well, looking at the shape of the signal did not convince me it was a grounding problem, and switching from a two secondary to a center-tapped one took care of the problem in my case. So I would not connect two transformers together directly.

 

[deduikertjes]

I would connect these through two rectifiers first and then pull the DC together.

For me this is definitely the better option. I tried both.

In my system neg. and pos. supply lines are not equally loaded en by this both transformers are not equally loaded, but connected to each other. This resulted in some mechanical hum in the transfromers. Going to two rectifiers cured that. This also cured the difference in output voltage for the pos. and neg. half of my supply. They are now within 0.1 V (was 1.8).

The resulting voltage under load was actually a little higher with the two rectifier option, so it's not sure if you'll lose to extra 1.4 Volts mentioned.

By the way on TNT audio the two rectifier option is preferred for 1 transformer with centretap as well. At least it takes some load of the rectifier.

greetings, MArco