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miklau  
#1 Posted : Tuesday, October 20, 2020 12:11:47 PM(UTC)
miklau

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HI TPA.

I have a slight DC offset on my IVY analog stage. It is not that much but after amplification in my class A amplifier i do have a DC offset. The offset is greatest on the left channel and when measuring on the balanced output. Very little on SE.The DAC is a COD and the source is from Ian FiFoPi. The I2S is wired through a OTTO1 selector switch (2nd input is your S/PDIF Transceiver module ).

Is there any way to correct this on IVY analog stage? Better match components or ad capacitors?

I used 0.1% resistors, wima capacitors and Nichicon electrolytic caps. OPA1632 and LME4562 are used. All parts are from digikey or farnell.
I have not fitted these components according to recommendation from Russ: IVY and COD SQ improvements
The IVY stage is powered by a Salas Ultrabib 1.3. This is trimmed to within 1 mV (+/- 15v). No ground loop found.

Best regards Mikkel

Resized_20180319_104706.jpg (166kb) downloaded 15 time(s).
Brian Donegan  
#2 Posted : Tuesday, October 20, 2020 1:38:02 PM(UTC)
Brian Donegan

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How much DC offset are we talking about? There will always be some.
miklau  
#3 Posted : Tuesday, October 20, 2020 5:07:29 PM(UTC)
miklau

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Hi Brian

Thanks for your reply.

DAC with no XLR cables connected:
Left: (+) 2 mV & (-) 3,3 mV
Right: (+) 3,8 mV & (-) 6,6 mV

Amplifier (Nelson Pass A75) with no XLR cables connected:
Left: 1 mV
Right: 3 mV

DAC connected to A75 with XLR (measured on the output of A75):
Left: 13 mV
Right: 74 mV
Playing Music:
Left: 65 mV
Right: - 3mV

Not sure why the small offset change when music is played and from right->left...?

All the measurements are pretty stable and verything is in working temperatur.
All XLR connectors are isolated from the chassis, both on the A75 and DAC.

Best regards Mikkel
Brian Donegan  
#4 Posted : Tuesday, October 20, 2020 6:39:26 PM(UTC)
Brian Donegan

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Those all look like very small (reasonable) values for both the IVY and the amp.

The values when connected are higher, still reasonable. You *could* try disconnecting the XLR ground to see if it helps, but nothing looks like it's out of place.
thanks 1 user thanked Brian Donegan for this useful post.
miklau on 10/25/2020(UTC)
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