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Autotransformer or Real Transformer, the pro's and con's

Posted by Thorsten (M) on November 25, 2001 at 04:39:38

In Reply to: with my very recent exposure to non-resistive attenuation posted by snkby on November 25, 2001 at 02:06:36:

Hi,

> just yesterday i replaced the alps model with a $30 radio shack
> 11 step stereo autoformer and am blown away by the clarity and
> dynamics.

Ohhh, that thing. It's not really that great, you know....

> thorsten says autoformer is not like transformer and i dont
> remember why exactly --

Well, there are a few reasons:

1) Autotransformers do not break any ground circuits and thus do not breal the noise loops, more RFI is the usual result.

2) Autotransformers are really suited only to unbalanced systems, well designed true transformers care little if they are connected balanced or unbalanced.

3) Auto transformers offer much less isolation between source and Amplifier and offer nowhere near the level of bandwidth limiting (limiting far out of Band signlas is a GOOD thing) and resilience against RFI.

In fact, the only reason to use Autotransformers I can see is pricing. It is much easier to make a decent Autotransformer than it is to make a full Transformer of equal quality.

> but i also remember reading someone saying that autoformer might
> be preferable for same reason.

I'd say other than lower price for the same performance no reason exists.

> i think my dreams of getting a pair of the s&b transformers are
> even further out of reach now that they are repricing. :(

Hell, some people buy Penny & Giles Potentiometers or build Stereo Attenuators with $ 100 switches and overall 96 pcs of $ 5 each Vishay resistors.... Don't be too cheap.

Ciao T

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