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Old 29th May 2010, 08:50 PM   #1
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Default Creating center tap from two transformers

I am specifically referring to this post here: 500va transfomer 3 secondaries no centre tap.

I didn't want to take the original thread too far off, so I opened this thread (@mods: please merge/delete/whatever however you please).

I found it annoyingly difficult to find center tapped xformers for a price that won't make me go broke. I was under the impression, that connecting the secondaries of two identical xformers would create the behaviour of a center tapped xformer. So is there no advantage to using two xformers in the aforementioned way?

Another catch: do I need to connect the secondaries in phase or 180 out of phase?
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Old 29th May 2010, 08:59 PM   #2
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Wire them in phase in series. Advantage: may be cheap for you. Disadvantage: size.
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Old 29th May 2010, 09:04 PM   #3
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Thanks!
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Old 29th May 2010, 10:11 PM   #4
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The original Crest 8001 used two transformers in series.

http://www.crestaudio.com/media/sche...matic_set1.pdf

See page 5. Crest used two rectifier bridges because they needed two tiers of output voltage.
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Old 29th May 2010, 10:20 PM   #5
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This looks like I could get that to work with my amp.
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Old 29th May 2010, 10:27 PM   #6
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Default I did this!

I used this configuration here Is it possible to build a good amplifier out of junk parts?(see photo), for not having the necessary transformer for testing purposes. I needed 24+24VAC, but had two 12+12VAC transformers.
It worked very fine, once both transformers were same type and specs. But the way I dit was a bit different from attached PDF: I linked them together in series before rectifier bridge.
You should try both cases, being aware that they should have the same output AC voltage, in order not to cause any difference between DC supply rails.
Regards,
Max.

Last edited by smartx21; 29th May 2010 at 10:34 PM.
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Old 29th May 2010, 10:57 PM   #7
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I was thinking of using two of those fellas here.
Those are the least expensive xformers I've ever used.

Thank you all.
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Old 30th May 2010, 11:40 AM   #8
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Dude,
If I read your cat. correctly, you have a transformer with just one 22.5 V winding tapped at 15,5 V (6.6 A) with about 150 VA total rating.
That might be a bit hard to find typical amplifier uses for. Then, maybe that's not what you want!
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Old 30th May 2010, 12:13 PM   #9
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forget the qsc schematic .... this doesnt use two transformers fro the same reason that you want to use them ...it is far more complicated than that

there is almost nothing wrong by using two of the same transformers to create a center tap ( while preserving phase issues )

in a previous thread it was mentioned by a forum member that is possible to have assymetrical clipping cause of that ... this can be possible stands as a statement but personaly i havent seen it hapening

regards sakis
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Old 30th May 2010, 04:34 PM   #10
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Quote:
Originally Posted by Ian Finch View Post
Dude,
If I read your cat. correctly, you have a transformer with just one 22.5 V winding tapped at 15,5 V (6.6 A) with about 150 VA total rating.
That might be a bit hard to find typical amplifier uses for. Then, maybe that's not what you want!
That's why he wants to use two of them...
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