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Old 24th August 2013, 06:27 PM   #1001
AndrewT is online now AndrewT  Scotland
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The transformer shield passes RF to the Chassis instead of, to the Secondary.

To allow this to happen effectively at RF the shield MUST be connected to the Chassis with the shortest possible wire to the nearest point right next to where the shield wire comes out of the transformer.
This may require the transformer to be mounted upside down to get that short wire connection.

DO NOT take a long wire to the Safety Earth.
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Old 24th August 2013, 08:57 PM   #1002
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I reconnected the shield wire and then ran a wire from center tap to chassis ground. No more issues.

Thanks
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Old 25th August 2013, 06:46 AM   #1003
emyeuoi is offline emyeuoi  Italy
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Default DC offset values

Today I complete and power-up the DCB1 but I am concerned about the offset values:

0,7mV and 2,5mV (?)

Those are the other values :

PSU: +10,28V and -9,81V

Vdrop across the 3 leds 5,551V and 5,546V

Vdrop across the 5 leds 9,662V and 9,198V

CCS resistor 2x27R - 1,739V and 1,697V

Any suggestion about the offset values?

Thanks,
Enrico
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Old 25th August 2013, 07:58 AM   #1004
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Much more important:
Is the output offset positive or negative?
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Old 25th August 2013, 08:46 AM   #1005
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Less than 10mV offset is usually considered OK.
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Old 25th August 2013, 08:57 AM   #1006
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AndrewT,
the output offset is +2,5 and -0,8

KatieandDad,
thanks for your reply... I go back in the thread looking for the offset values from the other builders... someone can reach 0,0mV so I suppose that somenthing is wrong in mine. Your answer make more confident on the results.

Regards and thanks on both of you.
Enrico
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Old 25th August 2013, 09:37 AM   #1007
AndrewT is online now AndrewT  Scotland
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swap the jFETs that show the +2.5mVdc offset.

You need a small negative offset to indicate that the upper jFET is passing ~99% to 100% of Idss.

If the offset is positive then that indicates that the upper jFET is passing >100% of Idss. This is reputed to be not good for jFET life and not good for jFET sound quality.
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Old 25th August 2013, 10:34 AM   #1008
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AndrewT,
you are talking about the 2 matched 2SK170 I suppose. Correct?
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Old 25th August 2013, 10:49 AM   #1009
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Unless the FETs are perfectly matched you will always get a small offset.
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Old 25th August 2013, 12:08 PM   #1010
emyeuoi is offline emyeuoi  Italy
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The 2 jfet are swapped.
Here the new reads...
The one that was +2.5 now is -1.6. The other one -0,6.
Thanks to everyone in the thread that make me in condition to realize this fantastic project.
I am finishing the F5TV2... I can't wait to earing the results!
Regards,
Enrico
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