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Fostex 6301 transformer balanced vs electrically balanced

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Fostex 6301 transformer balanced vs electrically balanced

Postby Uncle Freddie » Thu Feb 07, 2019 7:58 am

Hi,

I'm in the market for a Fostex 6301 monitor speaker.

https://www.fostexinternational.com/doc ... ries.shtml

They offer 4 types:

1. Transformer-balanced XLR input
2. Electrically-balanced XLR input
3. Unbalanced 1/4-inch TS input
4. AES/EBU XLR input

I don't need type 3 or 4, so it's down to type 1 or 2.

Is there an advantage to transformer balancing over electrical balancing?

(Wording question: I know "electrical" balancing as "electronic" balancing. They're the same thing, right?)

Thanks,
Fred
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Re: Fostex 6301 transformer balanced vs electrically balanced

Postby ef37a » Thu Feb 07, 2019 9:17 am

You are quite right in choosing a balanced input. The only real advantage of a transformer input is that it is likely to be more RFI proof than electronic balancing but unless you experience RFI problems in your area or are likely to travel to one such problems are unlikely.

The speaker uses a 3 pole IEC mains connector so the metalwork will be earthed. One other advantage of a transformer would be if the XLR were totally "earth free" but I bet pin one goes direct to earth (as it should in fact) and so that advantage, avoidance of hum/ground loops is lost. You can as easily disconnect the shield (NEVER MAINS EARTH!) wire for an electronic input as transformer.

Audio transformers are never quite as transparent as good electronics and these days are only used when absolutely necessary for RFI or ground loop isolation as mentioned but I doubt the shortcoming would be noticed in this application.

Dave.
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Re: Fostex 6301 transformer balanced vs electrically balanced

Postby Hugh Robjohns » Thu Feb 07, 2019 9:54 am

Both options 1 and 2 are 'electrically-balanced' because the signal is passed as an electric voltage in both cases... ;-)

The correct term in this context is 'electronically-balanced' -- it uses an active differential input amplifier to receive the balanced input signal rather than a transformer.

As Dave says, the transformer option potentially provides better RFI (interference) immunity and common-mode rejection, and can be used to provide galvanic isolation if the connecting cable is wired appropriately -- all things which can be of use in very difficult operating environments and it's a feature that some broadcasters would insist upon.

The downside is that the transformer adds weight and cost, and potentially also some slightly increased distortion...

The electronically-balanced alternative is cheaper, lighter and will have lower distortion, and while the RFI and common-mode specs won't be quite as good they will be more than good enough for 99% of normal applications.

Personally, I'd go for the electronically-balanced version without a moment's hesitation.

H
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Re: Fostex 6301 transformer balanced vs electrically balanced

Postby Uncle Freddie » Sat Feb 16, 2019 1:57 pm

Thanks Dave and Hugh.

-Fred
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