120V Sansui AU-G99X 530W Which transformer for 240V?

[Viczxcv]

Hello,

I have just bought this amp fro the USA. I am in the UK. Knowing little about electronics I want to run it safely with a suitable transformer. Different wattage models available and I was thinking of this one : -

https://www.amazon.co.uk/Power-Hero...sr=1-3-catcorr&keywords=step+down+transformer

an 1100 watt model/700watts for longer periods.

But I will never run the amp at half volume even, so will it be using 530 watts all the time or less depending on volume?

If less I could get a 700 watt transformer and save a bit of dough.

Any help appreciated.

 

[Sansui77]

Hello,

I have just bought this amp fro the USA. I am in the UK. Knowing little about electronics I want to run it safely with a suitable transformer. Different wattage models available and I was thinking of this one : -

https://www.amazon.co.uk/Power-Hero...sr=1-3-catcorr&keywords=step+down+transformer

an 1100 watt model/700watts for longer periods.

But I will never run the amp at half volume even, so will it be using 530 watts all the time or less depending on volume?

If less I could get a 700 watt transformer and save a bit of dough.

Any help appreciated.

Are you reading the 120V on the rear yellow sticker?

On the rear of the G99X, does your Sansui have this?

 

[Viczxcv]

Unfortunately no, it just reads 120v : 60hz. (530Watts 640VA). So, I guess it doesn't have the jumpers inside. Presumably made specifically for the USA market.
(I don't actually have it yet but the photos are good and clear of the back).

 

[JOMARK911]

Wait until you get it. It might be a multi voltage model and have the voltage selector internally.

 

[Viczxcv]

Thanks for the replies.

Yes, I had no intention of buying before receiving the item, but wanted opinions before it arrived so if necessary i will be ready to purchase.

 

[Viczxcv]

Bump

 

[Hyperion]

If the amplifier's power consumption is rated at 530W - I think this will be at full power output. However the rule of thumb when selecting or buying step down (or step up) transformers for audio (at least), is to give a very generous margin power rating wise, no matter how lightly you think you will be using the device to be powered from the 'step down'. So, I would say a 700W step down is barely adequate, and 1000W would be much better in this case.

But as Jomark911 says, "Wait until you get it. It might be a multi voltage model and have the voltage selector internally". - despite what it says on the rear panel.

BTW: Mine for 240V --->100V use was made to order by a local company, is rated at 1500W continuous, has 2 output sockets and a safety cut out, and is roughly half the size of the one pictured in your link. (but it did cost twice as much ).

Update:
The off load / on load voltages are 105 / 104 - I just checked.

 

[mbz]

I'd be a little cautious on that unit.
Suspect that it's an auto-transformer. Also, the output voltage is 110Vac/120Vac, which is it? no
selector switch. No datasheet. Need to know the no load output voltage. Mains voltage will bounce.

I'd be tempted to go for a isolated 1000VA step down for that amp

My generic post for stepdowns, added for info only,


Generally, there are 2 types of stepdown transformers. Non-isolated, autotransformer and isolated like the EI or torrodial.

From what little I know, 2 of the short comings of an auto transformer are,
- failure mode. Generally they will fail open circuit, this will (can?) cause the mains voltage to be presented to your audio device, generally means toast.
fyi, an auto transformer is a bit like a trimmer or volume pot except the wiper is in a fixed position. Variacs are auto transformers with a variable wiper.
- noise is the second issue, keep in mind some people spend money on power conditioners to reduce noise.

I recently built my own step down, after all it's just a transformer with a primary winding that must have the same rating as your mains supply. The
secondary winding must match the voltage of your audio device, eg, Primary=240Vac, Secondary=120Vac. The third part of the equation is the power
rating of the transformer, the so called VA (Volt Amps) rating. This is APPROXIMATELY equal to the number of watts of your device. A better
approximation is WATTS = V x A x 0.8 The 0.8 being called a power factor (I think) since voltage and current aren't in exact phase. Add fuses, a switch
power cord and a box and job done. I would advise against building your own unless you have very high end needs. It's cheaper to buy ready made.


Also, transformers are rated for a particular VA, so if you buy a 240Vac->120Vac 1000VA transformer, the secondary voltage will be 120Vac when
you are drawing 1000VA, which will be never. The no/low load voltage is typically 4% higher. An amp rated at 530W (consumption) will spend 99.9% of
its time consuming less than 200W, unless you dislike your neighbours, so don't over do the VA rating. Maybe someone can convince me why larger VA is
required, "on-demand" power, what ever that is...

Some equipment are switchable/configurable to different mains voltage (voltage selector at rear). Also some units can be easily rewired if they
have multi-voltage primary. Suggest open the unit up and take 2-3 hi-res photos of the transformer and immediate surrounds, however most likely
that USA models are hard wired to 120Vac, so stepdown required.

 

[Hyperion]

The no/low load voltage is typically 4% higher.

Update:
The off load / on load voltages for my example are 105 / 104 - I just checked.

I did see an explanation for the 'generous power rating' suggestion, but I can't remember the reason now.

A search finds this:-
"For instance, your imported oven toaster is rated at 1500 watts and runs on 110V power supply. If it’s rated in amperes, you’ll just have to do the math of conversion. Usually, the safest allowance of the transformer you can give is 3 times the wattage rating of your equipment. So the safest transformer that can support your oven toaster is a 5000 watts step-down transformer, step-down because MERALCO supplies us 220V and you have to transform it into 110V."

And
"This allowance is for safety purposes like in-rush currents".

And
https://www.tortech.com.au/choosingrightstepdown

There is a calculator here - entering 530W load, outputs 1000W as the correct step down transformer rating.

 

[Viczxcv]

Thanks for the replies guys.

Loads of transformers available but not many advertised specify whether they are isolated or not, or auto-transformers,etc..

I have been unable to find a datasheet on it. Always disappoints me when people want to sell things without giving full informaton on what it is they are selling.

Mbz you have me a little worried re auto transformers. I assume, from your post, that all torroidal transformers are isolated - so have been looking for one.

Even saw transformers, on a large chinese website, advertised as torroidal and then the same ones described as auto-transformers in other adverts! That website is notorious for misinformation.

Thanks for the info Hyperion. From what i can see double the appliance wattage is recommended generally; but triple is recommended for power tools and appliances with motors that may have a 'spike'
on switch on/off.

Not sure if it is allowed for me to post links to adverts (must read the rules) but I have found a torroidal 1000W at a reasonable price (£58 - $80) that is also smaller than the one I linked above. - Goldsource 1000W marked as
having 'Korean Technology' (on a well known auction site) that it states is also designed for continuous use (unlike the one liinked above). So, if i can't switch the receiver when I get it, I will probably go with that.

 

[restorer-john]

Buy another AUG99X and run the two primaries in series.

Seriously, get a stepdown that is isolated. Autoformers are not my idea of safe in the long term.

That said, an isolated secondary means your ELCB/RCD/Safety switch on your meter board is out of the picture in certain circumstances.

I'd go with a tightly regulated 1000VA- lots of copper and iron. Make very sure it is quiet when operating. Some are so noisy (buzz) that you can't use them in a quiet room.

I have a monster one here that I use for 100/120V repairs with 4 tappings on each side, but it rather noisy (buzz) . Can't forget to turn it off at least.

 

[mbz]

The no/low load voltage is typically 4% higher.

Update:
The off load / on load voltages for my example are 105 / 104 - I just checked.

Maybe I shouldtry to clarify.
Using a 1000VA 240 to 100Vac stepdown as an example.
The no-load voltage will be typically 4 percent higher, ie about 104Vac, this is to cover the iron losses etc shown in the datasheet.
4 % typical for torroidal, EI types slightly higher.
The stepdown is designed to deliver rated voltage at rated power, that is it will deliver 100VAC when drawing 1000VA.
Voltage will be higher if you don't draw rated VA because of lower current and IxR volt drop

Mbz you have me a little worried re auto transformers. I assume, from your post, that all torroidal transformers are isolated - so have been looking for one.

Autotranformers work ok, you might be lucky, someone is about to chime in saying they've used a 2KVA auto transformer for 20 years...
If the amp was precious to me (that one looks better than anything I've got) I would use an isolated type.

Sadly being torroidal does not mean isolated, some may be auto transformers. You need to check for the phrase dual winding.

And
https://www.tortech.com.au/choosingrightstepdown

I've seen the tortech site, there is some good info there. They have
two model types, their economy type eg, SD110-1010A (A=autotransformer) and their isolated type SD110-1000.

I would agree to wait until the amp arrives, open it up and check for any voltage selection options/switch or any capped transformer windings.
However US market are normally hard wired.

Basic questions,
does the stepdown have a single or dual winding (or is it an auto transformer)
what is the rated input voltage, many are 230Vac with 240Vac being within tolerances
what is the no load voltage, a 230Vac ->100Vac connected to 240Vac could be running at 112-114Vac, that's why this question is important.

 

[Viczxcv]

Buy another AUG99X and run the two primaries in series.

Seriously, get a stepdown that is isolated. Autoformers are not my idea of safe in the long term.

That said, an isolated secondary means your ELCB/RCD/Safety switch on your meter board is out of the picture in certain circumstances.

I'd go with a tightly regulated 1000VA- lots of copper and iron. Make very sure it is quiet when operating. Some are so noisy (buzz) that you can't use them in a quiet room.

I have a monster one here that I use for 100/120V repairs with 4 tappings on each side, but it rather noisy (buzz) . Can't forget to turn it off at least.

Well, would love to have another AUG99X - but don't seem to appear that often, at least here in the UK.
Still waiting for it's arrival.
If I end up with a noisy transformer at least I can put it on when the mother-in-law comes around.