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Nihilist 9th May 2009 09:03 PM

OPT grounding question
 
Is it necessary to connect the "negative" terminal of the OPT secondary side to chassis ground ? Seems as though the isolating properties of the OPT (isolating the load from the driver circuit) would be reduced or even eliminated.

Would it be OK to run the OPT's secondary connected only to the driver/load ?




Thanks for answering what will probably be a stupid question.




...............................Blake

SY 9th May 2009 09:35 PM

It depends. If you take feedback from the secondary then, yes, you need to ground the other end. If you're running open loop, no particular need.

Geek 9th May 2009 10:45 PM

If you're running open loop though, you'll still want a 1M resistor or so from one secondary leg to chassis to bleed the charge that develops from the inter capacitance of the windings.

Cheers!

Nihilist 9th May 2009 10:52 PM

I'm running open loop, triode tied 6V6's. FYI.


Geek said "If you're running open loop though, you'll still want a 1M resistor or so from one secondary leg to chassis to bleed the charge that develops from the inter capacitance of the windings."

Is this for safety reasons, as when handling the amp for servicing , or for performance reasons ?



Thanks guys...........................Blake

JandG 10th May 2009 12:05 AM

I am fairly sure if you try UL you need to slam the secondary ground to something. I supose UL is feedback of some sorts anyway. I remember some sqeal fests when doing some UL experiments when ground was not attached.
Joe

Geek 10th May 2009 10:49 AM

Quote:

Originally posted by Nihilist
Geek said "If you're running open loop though, you'll still want a 1M resistor or so from one secondary leg to chassis to bleed the charge that develops from the inter capacitance of the windings."

Is this for safety reasons, as when handling the amp for servicing , or for performance reasons ?


Safety.

I've received a nasty shock from equipment without it, even ones with top of the line trannies.

Not even servicing... just speaker wire in one hand, chassis in the other.

Cheers!

zigzagflux 10th May 2009 12:15 PM

When running open loop, I've seem some designs that wire equal resistors from each end to ground, kind of like a balanced system.

hemgjord 10th May 2009 10:54 PM

Safety!
 
If for some reason you have a insulation breakdown between pri and sec you will in most applications have B+ at your speaker terminals.
I strongly recommend grounding the secondary, that way you will blow a fuse or something else before you blow your self, your children, pets etc.

/Olof

Nihilist 12th May 2009 12:26 AM

Thanks for all the input .


Olof,

Do you recommend grounding the secondary directly to the chassis, or with a resistor ?





............................Blake

hemgjord 12th May 2009 09:09 PM

I normally ground the opt directly to the central star ground point, no resistors to ensure that you trip the fuse in case of failure. I generally don't think it matters much exactly where you ground it since it is not low level circuitry. Others may think differently.

/Olof


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