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No attenuation after major mess

delta1

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Re: No attenuation after major mess

Postby OliverD » February 5th, 2019, 5:13 am

I was measuring against the analog side.

Edit:
What I did find out is that this voltage somehow originates from the second s22 and always appears between chassis and input ground of the respective b22 board it is powering. Even when the delta1 is completely disconnected. The only difference between those two s22 boards would be the fact that one uses isolation pads on the MOSFETs while the other one doesn't.
Could this be the whole reason for this issue?

I will try to find some isolation pads, install them an recheck, but I might not have any at home.
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Re: No attenuation after major mess

Postby OliverD » February 5th, 2019, 12:02 pm

Okay, I have narrowed it all down to one b22 board. However I switch power transformers, cables and s22 around, it is always this one that I do get the 9V DC between chassis and input ground on the board itself.

Although this board passes the initial check and setup procedure and I cannot for the life of me find any shorts. I will revisit this board extensively on the weekend and then open a new thread in the b22 forums.
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Re: No attenuation after major mess

Postby amb » February 10th, 2019, 12:48 pm

When it’s all wired up, the input ground should be tied to the chassis at the Input jacks, if you followed the wiring diagram for a 2-chassis configuration. If they are indeed connected, then there shouldn’t be any voltage between the two points.
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Re: No attenuation after major mess

Postby OliverD » February 12th, 2019, 3:38 am

Yeah my bad, I suck at describing my problem. Sorry about that.

What I was trying to say was, that I can measure voltage between the ground plane of the b22 board and the chassis even when nothing's wired up except the power supply. Once I wire everything up correctly the transformer of the power supply for the problematic board starts humming very loud and gets hot (as were the ground loop breakers).

I must admit that I was only looking for shorts last time and like I said I didn't find any 0Ohm shorts... The b22 boards are all mounted to a bracket which in turn is mounted to an offboard heatsink, three of the boards are working perfectly while the fourth actually works when music is played through it to headphones, since the problem is all about the ground plane.
Well turns out that the bracket mounting was done sloppy or something else since there would not be about 26MOhms between the ground plane of the board and the heatsink/chassis as well as 26MOhms between chassis and the minus side of the power supply. Additionally there is 42MOhms or 12MOhms between chassis and plus side of the power supply (depending on which probe touches the chassis) which is especially weird to me. I will take this whole thing apart and try to find any scratches or other ways that there could be a connection between the boards ground plane and the chassis.

I keep getting the sense that I am in way over my head on this build and once this is fixed I will stick to reference builds instead of using my custom ideas ;-) Especially the offboard heatsinks of my Hifi2000 case were a bad idea for someone with zero experience in metalwork...
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Re: No attenuation after major mess

Postby OliverD » March 9th, 2019, 1:38 pm

Okay, just to give feedback on the whole thing:
Everything was indeed related to weird "pressure activated shorts" or in german "wackelkontakte" of sorts. The mounting brackets used to adapt the b22 output mosfets to kept getting shorted to PSU ground which in turn was responsible for the voltage on the input ground that fried the relais the same way it previously fried my HD650...

I have now waited until I had lots of free time, very carefully examined and isolated everything and it finally plays music again with working attenuation :-)

I can finally enjoy music on it again, but boy was this some costly overestimation of my abilities to handle metalwork and non reference builds... then again, mistakes is how we learn.
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Re: No attenuation after major mess

Postby amb » March 9th, 2019, 2:56 pm

I'm glad you got it all sorted out. :)
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