Convert 230 VAC amp to 120 VAC?? - diyAudio
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Old 5th February 2006, 11:35 PM   #1
chuck55 is offline chuck55  United States
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Default Convert 230 VAC amp to 120 VAC??

Hello, I have a Sony SRP-P50 50wpc (8 ohm) / 75 wpc (4 ohm) power amp that I would like to convert to 120 vac.
There is a single large torroidal transformer. Can I just switch this from 230 to 120 vac?
* How do I measure the output voltage? Is there a way to do this without powering up the amp because I don't have ready access to 230 volts.
* How do I determine the VA rating?

Thanks for any help.
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Old 6th February 2006, 01:51 AM   #2
clem_o is offline clem_o  Philippines
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Go ahead and power it up; measure the output voltage of the transformer. Multiply whatever you read by 2. It won't blow up if you power it with 110V.

Determine VA rating based roughly on output power capacity and output voltage.


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Old 6th February 2006, 02:39 AM   #3
kevinkr is offline kevinkr  United States
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Are you certain that this transformer doesn't have dual primaries that can be reconfigured for 120V? (A lot of Sony's don't unfortunately, but u never know..)
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Old 6th February 2006, 02:43 AM   #4
chuck55 is offline chuck55  United States
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Thanks Clem_o.
This amp can put out 150 watts @8 ohms bridged mono. People recommend 120 VA for a 40 wpc gainclone so tripling the 150 watts gives 450 va or triplig the 75 watts @4 ohms = 225 VA for a minimum.
I checked out the 500 VA Hammond is $90 and 70 for a 225 VA and the amp is only worth $250 so guess this will not be worth it.
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Old 6th February 2006, 08:54 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
If the transformer primaries can be rewired to suit 110Vac, then go ahead.
You will not damage the transformer by under running it voltage wise.

However there may be some components that will not switch on when only receiving about half voltage e.g. relays, Zeners etc.

The VA rating of the transformer will be reduced to about half if you run it unconverted i.e. 110 into 230. But this will not be an issue since if it will switch on it will now have only about a quarter of it's previous power. The main good thing:- it will run much cooler.

The old Sonys had a switchable selector for mains input voltage.
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Old 6th February 2006, 03:41 PM   #6
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This job shoulb be done with an ATOTRANSFOMER no a transformer, autotransformer will weitgh 50% of transformer and will cost 50% too.
So you could use an autotranforfer 50% of the weigth of the trannsformer in the unit.
You may measure the size with a ruler figure out the weigth with a transformer catalog from any company and then you will have a fair evaluation of the power.
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Old 7th February 2006, 12:34 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
He meant to say that you could use an autotransformer in front of your amplifier to convert your 110/120Vac upto 220/240Vac.
Then feed the amp and use it normally.
Some spare capacity in the auto could be used to power other 230Vac equipment.
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Old 7th February 2006, 01:04 PM   #8
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Quote:
Originally posted by chuck55
Thanks Clem_o.
This amp can put out 150 watts @8 ohms bridged mono. People recommend 120 VA for a 40 wpc gainclone so tripling the 150 watts gives 450 va or triplig the 75 watts @4 ohms = 225 VA for a minimum.
The power consumption of the amp is given as 160W in the specifications, and it's dated 1996 - unfortunately there's no manual on Sony Assist, just a very brief spec.
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Old 7th February 2006, 01:22 PM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
75W+75W into 4ohms totals 150W output.
Times 1.5 gives an approximate transformer requirement of 225VA. The 160W label rating confirms something of this order. For domestic music reproduction a 160VA rating should be acceptable. What this 160W also indicates is that the Sony amp is designed to work with 8ohm speakers (50W+50W=100W *1.5 =150VA) and the collapse of output voltage into 4ohm confirms it is not optimised for 4ohm duty, but will manage and not blow up.

An autotransformer of between 200VA and 300VA should perform well. It will be quite small and cheap.

Has anyone confirmed that the Sony transformer has single or double primaries?
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