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Old 12th July 2007, 10:08 PM   #1
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Default HELP Transformer, its configuration

Hi. first, sorry for my english.
I need a trasformer with two symmetrical out on secondary with one wire in common: the exit must be [24 0 24] volt do build a power source with dual voltage [-35 0 +35] volt.
I've ad ancient AKAI AM2400 and i want to utilize its transformer. I don't know if it work right, because I don't know his voltage on the secondary. In the photo there's the transformer with wires:

PRIMARY = BLU - WHITE - RED
SECONDARY = BLACK - YELLOW_1 - YELLOW_2 - VIOLET_1 - VIOLET_2

With tester I have these values:
YELLOW_1 & BLACK = 30V about
YELLOW_2 & BLACK = 30V about

Also the impedence is similare for these configurations (0.8 ohm about). Work this right? Is the out simmetrical? The void tension is 30V, but when I put it tn circuit, become it 24V about?

Please answer me, and show me the conformation of trasformator.

Bye. Thank you. Anthony.
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Old 12th July 2007, 11:30 PM   #2
v-bro is offline v-bro  Netherlands
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What do you want to use it for?
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Old 13th July 2007, 09:59 AM   #3
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I've to make a dual power source [-35 0 +35] volt about, to build an amplifier (mono) based on chip TDA7294.
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Old 13th July 2007, 10:24 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
your transformer has a guass band fitted around the coil. You don't often see that.

30Vac is the opencircuit voltage.
This is usually higher than the rated voltage for any transformer you buy.
The difference between the rated voltage and the opencircuit voltage is the regulation of the transformer (nothing to do with voltage regulators fitted after the rectifier).

your transformer is likely to be between 6% and 12% regulation.
This indicates a rated voltage of between 28.3Vac and 26.8Vac.

These supply voltages are right at the top limit for a chipamp driving an 8ohm speaker.
Did you note the mains voltage when you took the secondary readings?
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Old 13th July 2007, 10:46 AM   #5
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Hi AndrewT. Many thanks.. I didn't take other voltages, beacause I don't know the setting of trasformer. Can you indicate me? How couple of wair i have to test?

Bye.
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Old 25th July 2007, 07:21 AM   #6
gogs is offline gogs  India
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Default Also the impedence is similare for these configurations (0.8 ohm about). Work this ri

The Akai 2400 Transformer is underrated as i think the amp is only 20W +20W both channels driven, for your TDA 7293 (100WRMS) although you could only use it for testing, be sure your DC rails do not exceed +- 50V before making a final connection .I would recommend you order a Tranformer of the correct rating if you are seriously building this up or you may end up building a Marshall MG100 guitar amp you modify to current feedback.
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Old 25th July 2007, 08:19 AM   #7
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Yes gogs, I've take a right trasformer for my build. I will use the AKAI one for other build. Thanks.

Bye.
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Old 25th July 2007, 09:18 AM   #8
AndrewT is offline AndrewT  Scotland
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Default Re: Also the impedence is similare for these configurations (0.8 ohm about). Work this ri

Quote:
Originally posted by gogs
The Akai 2400 Transformer is underrated as i think the amp is only 20W +20W both channels driven, for your TDA 7293 (100WRMS) although you could only use it for testing, be sure your DC rails do not exceed +- 50V before making a final connection.......

Quote:
Originally posted by gamberone
I've take a right trasformer for my build. I will use the AKAI one for other build.
Hi,
if the old transformer gives +-35Vdc to +-40Vdc without an amplifier connected to it, then use it for testing.
If that old amplifier was indeed for a 20W+20W stereo amplifier then it should work reasonably well driving a 50W chipamp IF THE VOLTAGE is right.

Measure it again. Connect up a bridge rectifier and some smoothing caps and measure it yet again. Remember to check the mains voltage at the same time as you take any other measurements.

If each of the transformer wires are inserted into a terminal block, you can carry out these tests safely, but do take care while working with mains voltages.
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