500va transfomer 3 secondaries no centre tap - diyAudio
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Old 27th May 2010, 03:45 AM   #1
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Default 500va transfomer 3 secondaries no centre tap

I have a transformer with 3 secondaries 24vac 30vac and 34vac and i would like to use it for a 200 watt amplifier. I don't understand how to get a centre tap from this transformer or if i can parell the secondary's up to get it or what the best option is to use is it has a configuration like this

____ 0 volts

____ 24 vac

____ 30 vac

____ 34 vac

The transformer is 500va surely there must be a way i can hook this up and use it for my amplifier if anyone can help me with a schematic on how to do this it would be greatly appreciated.
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Old 27th May 2010, 04:37 AM   #2
infinia is offline infinia  United States
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The way you describe the XFMR is that it has one secondary winding with 2 Taps. There is no tap at 1/2 so there is no way to get balanced or centered DC supplies. One way to maximize the transformer and power out is to develop a single DC voltage DC using the maximum 34VAC. Using a full bridge rectifier and single large cap to produce a single supply 0.95(34x1.4) - 2Vdiode or ~ 43 Vdc. so not nearly enough voltage to get 200 W into 4 ohms. There are capactor coupled output bridged amps to get the most out of this XFMR for audio giving close to 200W at 4 ohm.
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Old 27th May 2010, 07:38 AM   #3
AJT is offline AJT  Philippines
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you can use a full wave voltage doubler on the 0-34vac to get, +/-43 volts....not enough to get you 200 watts .....
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Old 27th May 2010, 08:48 AM   #4
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Voltage doublers are not suited to deliver current.
From a 47.6 v (= 34v x 1.4) single supply , it is possible to build an about 75 watts/8ohms bridged amplifier.
Paralleling two such amps would give 150 watts. Though this would need 4 identical modules per channel.

Last edited by bobodioulasso; 27th May 2010 at 09:06 AM.
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Old 27th May 2010, 08:51 AM   #5
AJT is offline AJT  Philippines
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that is true...we are merely discussing possibilities here...
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Old 27th May 2010, 09:12 AM   #6
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Quote:
There is no tap at 1/2 so there is no way to get balanced or centered DC supplies
There is one way: Google for Quad 606 or 909 schematic and look at PSU.
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Old 27th May 2010, 12:49 PM   #7
wg_ski is offline wg_ski  United States
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Next time, buy two.
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Old 27th May 2010, 01:31 PM   #8
sregor is offline sregor  United States
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2 full wave bridges, run of the the zero and 34 volt tap. One bridge for positive, one pridge for negative. Or 2 single diodes, one for plus and one for minus, and large filter cap (half-wave rectifier). Then bridge output. If stereo, pushes power limits on transformer - but would be OK for music. YMMV. My 2 cents.
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Old 27th May 2010, 01:33 PM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by sregor View Post
2 full wave bridges, run of the the zero and 34 volt tap. One bridge for positive, one bridge for negative.
no.
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Old 27th May 2010, 08:47 PM   #10
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You could sell the transformer on ebay and buy a double secondary transformer.
Saves a lot of messing about.
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