Pseudo Balanced TVC/AVC

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gnnett

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Pseudo Balanced TVC/AVC
« on: 29 Nov 2014, 09:45 am »
Hi

TVC's have typically been used as balanced by floating the secondary windings, rather than using 2 transformers. This is not done with AVC's. My question is, if the input is already balanced, is it possible to leave the windings floating to provide balanced output using a single AVC, or will this simple not work?

Regards

Gnnett

John Chapman

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Re: Pseudo Balanced TVC/AVC
« Reply #1 on: 1 Dec 2014, 12:51 am »
Hello!

With autoformers we do balanced with 4 units rather than 2 - so it is a true balanced attenuator and not floating balanced (differential) . You can't just float one side like you describe and use 2 of them...... I did a bit of a blurb on balanced / rca connections with autoformers a while back here:

http://www.audiocircle.com/index.php?topic=118431.0

Post any follow up questions and i will do my best to reply.

Thanks!

John

Armaegis

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Re: Pseudo Balanced TVC/AVC
« Reply #2 on: 18 Dec 2015, 06:54 pm »
You can't just float one side like you describe and use 2 of them......

A bit of a thread revival, but I have a followup question(s): why can't we float the secondaries of the AVC? what exactly happens on the output? Why does it work for a TVC but not an AVC?

I can see some weirdness occurring if we shared the negative leg and connected that directly from the dac to autoformer "ground" to amp input... but what if we used a separate secondary tap as the negative output? (argh I need a picture to illustrate; it's confusing in words)

JohnR

Re: Pseudo Balanced TVC/AVC
« Reply #3 on: 18 Dec 2015, 11:40 pm »
Hi, it's because a transformer has a separate (electrically isolated) secondary winding, whereas an autoformer has only a single winding.

Armaegis

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Re: Pseudo Balanced TVC/AVC
« Reply #4 on: 19 Dec 2015, 07:24 am »
Yes, that part I get. What I want to know is what will happen if I wire up an autoformer? What kind of signal is passed?

excuse my extremely poor mspaint skills


what if the output legs are equidistant from the ends? does it retain a sense of "balance"?

what if the negative output is connected directly to the neg input? I'm sure there's still some sort of signal being generated, but what's happening and why is this not allowed?