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avr300  
#21 Posted : Monday, October 21, 2013 5:42:52 PM(UTC)
avr300

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Try disconnecting those headphone connectors (or float them).

Remember, best use star ground schema - and if you insist grounding your chassis, do it in one spot only.

Don't mix up protective earth (PE) and signal ground.
kwhubby  
#22 Posted : Monday, October 21, 2013 7:37:30 PM(UTC)
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I can try this, I will let you know if I get any luck. I am using a star grounding scheme, but I still have trouble. With such high frequency response of these parts up to 180mhz, a multipoint grounding scheme starts to look better to me than a star grounding scheme.

The more I look at this the more I suspect stray capacitance on the input pins, since my feedback resistor is considerably higher than the original design.

kwhubby  
#23 Posted : Tuesday, October 22, 2013 8:51:03 AM(UTC)
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A quick follow up. I disconnected the headphone connectors from the chassis, and crudely grounded them to the ground holes on the "signal side" of the board (where input and output holes are located). Now the sound is at least 36db subdued but very faintly audible on the right side if everything is quiet. I would say this is entirely usable, but I think I should scope out board to make sure it isn't strongly oscillating at RF frequencies again or ringing on audio signals.
Now I need to figure out a way to isolate these metal connectors and screws from the metal chassis, I suppose electrical tape should work.
Thanks!
avr300  
#24 Posted : Tuesday, October 22, 2013 7:59:58 PM(UTC)
avr300

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What kind of headphone connectors are you using ?

I'm using one of those:

http://www.neutrik.com/e...cking-1-4-chassis-jacks/

The metal chassis of this connector is NOT connected to signal ground (no ground loops involved).
kwhubby  
#25 Posted : Tuesday, October 22, 2013 8:54:33 PM(UTC)
kwhubby

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I'm using an old style surplus switchcraft connector I got for 50 cents. It is very sturdy and solid contacts, but is quite large, open frame and grounded metal body.
I love the neutrik connectors, but they have gotten so expensive! I used to know a website that sold everything neutrik at a good price, but now everything is at least 50% more expensive. You wouldn't happen to know where to get the best deal on neutrik stuff would you?
(edit: I see you are in Denmark, neutrik may be a better value where you are)

Edited by user Tuesday, October 22, 2013 10:41:19 PM(UTC)  | Reason: Not specified

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