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Old 11th July 2003, 04:46 PM   #1
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Default Grounding OPT secondaries?

Yes? No? Are there sonic pros and cons? Are there safety issues? Does it depend on whether the amp uses a negative feedback tap from the secondary or not? Does it differ for PP vs. SE? Does it matter which secondary lead is grounded?

I've seen some SE schematics that ground the OPT secondary, and some that don't. So, there doesn't appear to be a hard-and-fast rule about how to do this. I'd appreciate any advice on the different factors that would influence this decision.

Thanks,
Saurav
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Old 11th July 2003, 05:17 PM   #2
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Let's look at two cases:

1. No loop feedback from the secondary. It won't matter much whether or not one side is grounded.

2. Loop feedback from the secondary: Either one side is grounded or the center tap is grounded. The latter is the preferred way for fully balanced and quasi-balanced circuits.
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Old 11th July 2003, 05:24 PM   #3
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OK, my amp doesn't have a feedback tap from the secondary. When you say "it won't matter much"... I guess that means I could try grounding the secondary to see if it makes a difference? Can it make any difference with noise issues? And the CT on the secondary, that would be the tap that gives me half the impedance, right? Or the middle tap, assuming the impedance values are evenly distributed across the taps. I could try grounding that too.
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Old 11th July 2003, 05:40 PM   #4
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If your transformer has the usual 16, 8, 4, C taps, the 4 ohm is the center tap.

Noise issues in speaker cabling can happen, but it's pretty rare. It never hurts to try a couple grounding schemes and see if one is better than the other.
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Old 11th July 2003, 06:01 PM   #5
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Thanks.
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Old 11th July 2003, 07:03 PM   #6
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If the transformer isn't very good, there can be P-S leakage, and without a load on the secondary, it can be charged to high voltage! Never hurts to ground it.

Tim
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Old 11th July 2003, 07:12 PM   #7
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Since O/P transformers have interleaved primary and secondary windings, a grounded secondary is effectively an E/S screen between different sections. Why not apply a square wave and look at the leading edge to see whether grounding the secondary makes a difference, and whether it's benign or malignant?
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Old 11th July 2003, 07:28 PM   #8
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Default grounding

Thread from a couple days ago by K.Strain


http://www.audioasylum.com/forums/tu...ges/33386.html


Cheers
Craig Ryder
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Old 11th July 2003, 07:41 PM   #9
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I saw that AA thread when I was searching for info on this topic yesterday.

I need to pick up a cheap function generator. I checked my local electronics surplus store a few days ago, and all they have is something that's accurate out to 2MHz, and costs $250. I've seen some on eBay for $30 - $50, but there weren't any on there yesterday. I have a scope and I've used it a few times, a function generator is next on the list.
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Old 11th July 2003, 07:46 PM   #10
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Crikey! $250 for a function generator? $150 for a new one. I paid 80 for mine.
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