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bhjazz  
#1 Posted : Thursday, January 2, 2020 5:39:53 AM(UTC)
bhjazz

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I recently put my Ventus into a new chassis, but am getting ground noise.
The new chassis is aluminum with 1/4 inch front and rear panels.
The power ground is connected to a spot on the bottom panel where the signal ground is connected.
The signal ground has a ceramic resistor and a cap that total about .2 ohm when measured.
This is connected to isolated input RCA terminals, and from there connected to an Alps Blue Velvet volume pot.
That connection is also connected to the Blue Velvet chassis screw on it's back.
The output jack is isolated.
The left and right Ventus boards have their grounds connected together.

DC Offset:
Left board: 0.009
Right board: 0.011

I can stop the ground noise completely if I use a 1/4 to 1/8 inch converter for, say, a pair of Grados, and touch the metal of the converter plug.

I have tried connecting the chassis of the Blue Velvet to the ground of the 1/4 inch output plug, but this changes nothing.

Do I need the caps on the signal ground connection? Maybe larger caps?

Oddly enough, the noise is slightly higher in the left channel than the right.

I've tried quite a few test connections, but still have not found (or stumbled upon) the right combination. Brick wall Sortof hilarious.

Any suggestions?

Thanks!

Edited by user Friday, January 3, 2020 3:46:34 AM(UTC)  | Reason: Not specified

Brian Donegan  
#2 Posted : Monday, January 6, 2020 8:31:26 PM(UTC)
Brian Donegan

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Hi. A picture would be helpful.

The one ground you absolutely need is the power ground/Earth to the chassis.

Ground loops occur when you provide multiple paths for elections to flow to ground.

I personally like to keep my signal grounds (in low voltage applications like this) completely isolated from power grounds. I use isolated RCA input jacks, connecting them directly to the volume pot, then to the Ventus boards. If the boards share a ground, share it at the output of the power supply(s) and nowhere else. I would then route the Ventus outputs to isolated output RCA jacks.

Give that a try and see if you still have noise.


[EDIT]: It is also possible that one or both boards is missing it's signal ground (bad connection) which can also cause noise in single-ended setups.

Edited by user Monday, January 6, 2020 8:33:14 PM(UTC)  | Reason: Not specified

bhjazz  
#3 Posted : Tuesday, January 7, 2020 3:42:56 AM(UTC)
bhjazz

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Will do, Brian. Thanks for the suggestions.

I'll take a close look at my build and see where I have committed the crime! If I find that the problem is still there after some changes, I'll get a picture posted. More soon. Thanks!
bhjazz  
#4 Posted : Wednesday, January 8, 2020 5:00:41 AM(UTC)
bhjazz

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Ok, first off, I had the grounds of both boards connected to each other. That was removed.

I also disconnected the signal ground connection to the chassis ground. No dice, although oddly enough the noise which was normally in the left channel shifted to the right. That may be a clue later.

With the signal ground disconnected, the buzz/noise is slightly less, but gets worse when I touch the cheater plug. I find this interesting since it is the opposite of what I encountered when it was connected.

I removed the Alps blue velvet volume pot from the chassis as a test but left it connected to the circuit. I also removed a connection between the Alps ground lugs and the alps case. Neither change made any difference.

So the good part is that I removed some potential problems, but the bad part is none of them solved my original issue. With that in mind, I'll add some photos. I need to go find a new photo hosting site. I haven't done that in years!

Cheers!

EDIT: The only signal grounds I am using are the incoming connections from the unbalanced RCA, which are summed to a single lead and sent to the Alps input side. The Alps input and output grounds are connected together, which are then connected to the right channel Ventus board. A ground connection is then connected from the same right channel Ventus board to the output jack.

Edited by user Wednesday, January 8, 2020 5:15:17 AM(UTC)  | Reason: Not specified

bhjazz  
#5 Posted : Thursday, January 9, 2020 3:58:14 AM(UTC)
bhjazz

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Let me know if you'd like any detail photos such as the Alps connections or whatever. Maybe the backside of the boards?


The general layout
UserPostedImage

Isolated RCA inputs
UserPostedImage

Backside view of front panel
UserPostedImage

Actual board wiring
UserPostedImage




Many thanks!
BH
Brian Donegan  
#6 Posted : Monday, January 13, 2020 9:01:21 PM(UTC)
Brian Donegan

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UserPostedImage

First question: what is that filter board (with the caps)?

Second, one the board on the left, there is a signal ground at both input and output. The board on the right there is no signal ground. Where do these lead?
bhjazz  
#7 Posted : Tuesday, January 14, 2020 3:54:54 AM(UTC)
bhjazz

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Ok, I bought/won the amplifier from Nate Maher on Head-Fi in 2010. Most of the info regarding his build of the amp is there, but I can answer a few of your questions without making you read that entire thread!

Nate's post is here for reference: https://www.head-fi.org/threads/...sted-pear-ventus.513379/

Nate says, "...The amp is cap-coupled (not a part of the original design) because I wasn't comfortable with the amount the outputs tended to drift. It never went above 20mV but I wanted whomever ends up with this to be able to use it worry free and not have to make adjustments."

So in my project to move this build to a different case, I duplicated his original design. I changed the output caps (brand only, not value) and added a bypass cap since it was staring at me.


For your second question: The input ground comes from the Alps blue velvet. The output ground from the board is connected to the isolated output jack.

Earlier in this thread I had connected the input ground from one board to the other (that is, from left channel to right channel) but in removing it I had no change. I removed this in reference to your comment, "... If the boards share a ground, share it at the output of the power supply(s) and nowhere else."

Maybe I should have connected the output grounds instead of the input grounds? Still, this would not duplicate Nate's original build, so I'm probably missing something else.

Thanks!
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