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Old 8th August 2008, 08:53 AM   #1
Buzzy is offline Buzzy  Singapore
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Default Center tapped transformer help

I have a 24-0-24 transformer . The secondaries of the transformer have 24, 0, 24 wires. This is called center tapped right ? Can i connect the two 24Vac secondaries to a bridge rectifier and get +35V and -35V and ground from this type of connection ? The transformer primary is 230. My mains are 240V.
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Old 8th August 2008, 09:16 AM   #2
AndrewT is online now AndrewT  Scotland
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Yes. +-35V is available from 24-0-24Vac.
Use a single bridge rectifier across the 24-24 tappings.
Connect a pair of series smoothing caps across + to - of the rectifier.
Connect the centre tap to the junction between the two series caps.

I would expect your 230:24Vac transformer to measure about 26Vac to 26.6Vac (open circuit) when on your 240Vac supply.
This should give between +-35Vdc and +-36.5Vdc when lightly loaded.
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Old 8th August 2008, 09:35 AM   #3
lineup is offline lineup  Sweden
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Default Re: Center tapped transformer help

Quote:
Originally posted by Buzzy
I have a 24-0-24 transformer . The secondaries of the transformer have 24, 0, 24 wires. This is called center tapped right ? Can i connect the two 24Vac secondaries to a bridge rectifier and get +35V and -35V and ground from this type of connection ? The transformer primary is 230. My mains are 240V.

Click the image to open in full size.

Quote:
For the 60W amplifier, a nominal (full load) supply of +/- 35V is required,
so a 25-0-25 secondary is ideal - however, see Updates, below.

The circuit for the supply is shown below, and uses separate rectifiers, capacitors and fuses for each channel. Only the transformer is shared, so channel interactions are minimised. A single 35V supply (i.e. using only a single bridge and set of filter capacitors) will work just as well in the majority of cases.
The image is from Rod Elliott site.
http://sound.westhost.com/project04.htm
He has got many examples how to make a good dual rails supply.
The image above shows using
one center tapped trafo .. to supply 2 power amplifiers.

For one power amplifier (using 1 trafo per channel)
you only have to use one bridge rectifier + caps = half the circuit.
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