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Old 10th February 2014, 11:18 AM   #1
frangus is offline frangus  Australia
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Default Help with Rotel voltage reconfiguration

I have a 120V ROTEL RB-976 that I need to convert to 240V.

The manual states:

"Should you move your RB-976 amplifier to another country,
it is possible to reconfigure your amplifier for use on a differentline voltage"


Which sounds like there may be a jumper in the unit to reconfigure it.

I had a look inside and see the transformer has 120V, 230V and 240V wires all connected to the board (see photos). However I cant find any jumpers.

Can anyone shed some light on this?

Thanks
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Old 10th February 2014, 11:27 AM   #2
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Do the orange, blue and brown wires all say AC0 next to them? The photo is small and the legend for the blue wire is hidden from view.

It would appear that you need to desolder the orange wire and brown wire and swap them round, but I would have thought the orange wire would have a legend other than AC0 if that was right.
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Old 10th February 2014, 11:36 AM   #3
frangus is offline frangus  Australia
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Thanks, that makes sense.

Each wire has a different number - AC8 for the orange and AC9 for the brown etc

Is it possible that the amp can automatically detect input voltage, and that is why all the wires are already soldered to the board?

I suppose I will have to replace the fuses as well, to 240V spec.?

cheers
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Old 10th February 2014, 11:47 AM   #4
Mooly is offline Mooly  United Kingdom
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It definitely won't automatically change from one voltage to another. Fuses are general around half the current rating when going from 120 to 240 volts.

You need to be sure... if there is ANY doubt then make a note of ALL the secondary's and then isolate them ALL. Fit a low wattage "bulb tester" to the primary and then when you have altered the primary as you think fit power the transformer up and check the voltages are as expected. Any mistakes will just light the bulb and cause no damage.
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Old 10th February 2014, 12:06 PM   #5
frangus is offline frangus  Australia
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could you clarify isolating the primary and secondary of the transformer? I'm keen to learn this but don't understand all the practicalities as yet. Thanks

ps what's the worst that could happen if I swap the Orange and Brown and just plug it in? I thought the fuses would protect the amp?
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Old 10th February 2014, 12:08 PM   #6
frangus is offline frangus  Australia
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Just checked, the board label near the fuse and it specifies the current rating for a 240v as 3A, half the 120v rating as you said.

Last edited by frangus; 10th February 2014 at 12:11 PM.
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Old 10th February 2014, 12:23 PM   #7
Mooly is offline Mooly  United Kingdom
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The primary windings are all the connections on the MAINS side of things. The secondary connections are the low voltage winding that power the amplifier.

Do you have service manual or circuit for this amp ? If you can come up with one then that might make it clearer.
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Old 10th February 2014, 12:30 PM   #8
Mooly is offline Mooly  United Kingdom
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Look at this closely which shows your amp. You keep "AC10" where it is. You move AC8 to the top winding.

TURN THE AMP OFF AND UNPLUG FROM MAINS.

If you connect your meter (on low ohms range) to AC10 and measure the resistance to each of the other windings you will see the resistance gets higher and higher. For example it might read 5 ohms as drawn, 6 ohms as you measure to the next winding up, and 8 ohms as you measure to the top winding.

The 240 volt setting is the HIGHEST resistance setting. In other words all the windings together.
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Old 11th February 2014, 11:07 AM   #9
frangus is offline frangus  Australia
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Thanks Mooly, nicely explained.

It measured as you said, with the 240v Brown wire showing the highest resistance on the meter.

So now I can safely do the swap?

I'll still need to replace the fuses and connect a new plug of of course.

cheers
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Old 11th February 2014, 11:29 AM   #10
Mooly is offline Mooly  United Kingdom
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You are welcome

Yes, it should be good to go now.
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