cheap transformer or cheap death?

[CharlieLaub]

I have been dreaming of getting a particular 600W class D amplifier module that can operate off of up to 84V rails. I realized that 84VDC can be obtained from rectified 60VAC. I know that there are many super cheap step-up/step-down transformers that just have a 2:1 turns ratio and I could connect that to my USA power grid @120VAC to get out 60VAC, which I would rectify to get my rails. Then it also dawned on me that these might be cheap because they are actually autoformers, which don't provide any isolation. This means shock danger if there is a fault.

So, can I use a cheap step up/down transformer or should I avoid because they are autoformers? Should I just avoid step-up/down transformer (not necessarily autoformers) in general because of other reasons???

-Charlie

 

[metalsculptor]

Avoid at all costs, the ground will not be at a similar potential to the neutral, and something nasty will happen.

 

[CharlieLaub]

Well I found a web page that confirms my fears...

Never Use a Surge Protector with a Step-Down Transformer

I will definitely avoid getting a power supply transformer on the cheap by using a $19.99 step up/down transformer from Ebay!

-Charlie

 

[DigitalJunkie]

Also,assuming your amp needs +/- 84V rails,you'd be short a rail,unless you used half-wave rectification,which is less than ideal.

 

[AndrewT]

do you have 110Volt isolation transformers for safe use of 110V power tools outside?

In the UK these are 240:55-0-55Vac
Ideal for this duty. Available from 500VA to 5kVA.

 

[Th3 uN1Qu3]

He's in the US and has 120v power.

 

[ratbagp]

You might consider industrial transformers which are commonly available on ebay. They are not autoformers.

The bigger ones are naturally very heavy.

ray

 

[Enzo]

You are assuming the things MIGHT be autotransformers because they are cheap. Then you are basing a lot of things on that assumption being true. WHy not FIND OUT if they are autoformers, or not, first.

 

[semi932]

From another angle, you could look for vintage or newer high powered receivers not working from thrifts or yard sales.
I've salvaged many large high quality transformers from the like.

Not always easy to find but they are out there.
Saves bucks as we know the transformers are usually the most expensive part of DIY.