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VOLTAGE REDUCTION TO OPTIMISE STEP DOWN TRANSFORMER

supercaley

Oct 6, 2021
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Hi, new here and ignorant on matters electrical but have seen some interesting threads and you seem to be a helpful bunch, so here goes..
I am UK based and purchased a vintage 1970's Japanese audio amplifier which requires 100v as opposed to the circa 230-240v from my mains supply.
I purchased a UMI 1000w step down transformer 220v - 100v (allegedly for UK travel from Japan). It has a display of the voltage output which consistently shows 110-112v output when plugged into my domestic sockets. I assume the higher output is because of the source input being higher than 220v, ie 230-240v?
My question is, rather than purchase another transformer which would be expensive given the wattage I require, is there a simple, safe and reliable way to effectively reduce the mains voltage by eg sharing the load or using a long extension cable that would enable my step down transformer to bring the voltage down by 5-10v to close to 100v?
 

Harald Kapp

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Your amplifier should be happy with 110 V - 112 V. 10 % is usually well within the tolerance of such a component.
 

Minder

Apr 24, 2015
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One none invasive way, IF you found you needed it, is a Buck-Boost transformer with a 5v or10v secondary
 

dave9

Mar 5, 2017
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While I can appreciate wanting to keep something stock, I think I'd have as soon swapped the existing transformer.
 

crutschow

May 7, 2021
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One none invasive way, IF you found you needed it, is a Buck-Boost transformer with a 5v or10v secondary
To elaborate on this, it can be done with a 220V to 10V transformer.
The 220V primary side is connected to the 220V mains, and the 10V secondary side is connected in series with the 110V output with opposing polarity to reduce the total voltage (experiment to determine the correct polarity).
The secondary output current rating of the 10V transformer should be some more than the maximum current rating of your amp.
 

Mver40

Oct 7, 2021
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Oct 7, 2021
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Hi, new here and ignorant on matters electrical but have seen some interesting threads and you seem to be a helpful bunch, so here goes..
I am UK based and purchased a vintage 1970's Japanese audio amplifier which requires 100v as opposed to the circa 230-240v from my mains supply.
I purchased a UMI 1000w step down transformer 220v - 100v (allegedly for UK travel from Japan). It has a display of the voltage output which consistently shows 110-112v output when plugged into my domestic sockets. I assume the higher output is because of the source input being higher than 220v, ie 230-240v?
My question is, rather than purchase another transformer which would be expensive given the wattage I require, is there a simple, safe and reliable way to effectively reduce the mains voltage by eg sharing the load or using a long extension cable that would enable my step down transformer to bring the voltage down by 5-10v to close to 100v?

SOLDER A RESISTOR INLINE WITH THE OUTPUT OF STEP DOWN TRANSFORMER.USE YOURE MULTIMETER TO VERIFY VOLTAGE.
 

bertus

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Nov 8, 2019
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Hello,

@Mver40 , A resistor may not be the best solution.
The voltage after the resistor will vary with variations in the load.

Bertus
 

Bluejets

Oct 5, 2014
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I purchased a UMI 1000w step down transformer 220v - 100v (allegedly for UK travel from Japan). It has a display of the voltage output which consistently shows 110-112v output when plugged into my domestic sockets

Is that under any load or just floating?
Transformer will always have a higher output under no load, especially smaller units.
 
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