PPA:Does this sound right?
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jerry1130

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First of all I would like to thank MisterX and Tangent for helping me out with my TEPS. Now I got my PPA going, its got some issues:

1.The DC offset form IG to OG is 0mv, IG to OR is -0.3mv, and IG to OL is 1.3mv. Are these values fine or could there a problem? The amp sounds fantasic even with these values.

2.I am getting some buzzing from the amp only if no source is pluged in, the amp is dead slient if source is plugged in. The pot is grounded to ground pad so grounding is probably not a issue.

Any ideas?
 
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jasonhanjk

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The OL is a bit high. You may like to check for proper biasing of OL and is there flux residue. Most of the time it should be ok.

Did you use signal ground for shielding onto the PPA casing?
 
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Garbz

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the output offset is just fine. Anything below 0.1V is apparently fine according to Grado and they are very sensitive heapdhones.

the 1.3mV wouldn't make much of a difference at all.
 
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morsel

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Quote:

I am getting some buzzing from the amp only if no source is plugged in, the amp is dead slient if source is plugged in. The pot is grounded to ground pad so grounding is probably not a issue.


Grounding is definitely the issue. I suspect you did not tie the case to signal ground. See my notes on wiring considerations for more details: http://elvencraft.com/ppa/
 
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morsel

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duplicate, please delete
 
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jerry1130

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The PPA isn't acutally in a case right now, could it be that? Also I am using opa627/637 with gain of 11, one buffer per channel right now.
 
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IpsilonSound

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Quote:

Originally Posted by jerry1130
1.The DC offset form IG to OG is 0mv, IG to OR is -0.3mv, and IG to OL is 1.3mv. Are these values fine or could there a problem?


These values are fine, I had pretty much the same and doubt if anyone had equal values on both channels. When you apply signal, the voltage varies from - to + within several milivolts depending upon the signal.


Quote:

Originally Posted by jerry1130
2.I am getting some buzzing from the amp only if no source is pluged in, the amp is dead slient if source is plugged in. The pot is grounded to ground pad so grounding is probably not a issue.


When I assembled my first amp, without the case it was buzzing too when the input wasn't connected to the player, especially when the soldering station was turned. When I put everything into the case and grounded the common signal path, it became quiet. In your case the buzzing continues after putting it in the case, so it's probably the grounding issue, I think.
Grounding is VERY important in PPA, many DC jacks have '-' input designed so it will be connected to the case of the unit. I had to use insulation to prevent this.
What happens when you short its input, right/left to ground, buzzing goes away?
 
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