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Pass Labs Pearl Hum advise/help
Pass Labs Pearl Hum advise/help
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Old 8th June 2020, 01:27 PM   #21
jamayfie is offline jamayfie  United States
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Pass Labs Pearl Hum advise/help
Quote:
Originally Posted by creed2 View Post
I don't know what type of wire previous owner used to run from ground jack on back of pearl for tonearm/turntable ground but it does not conduct a signal to ground on chassis of pearl on my ohm meter. Even touching just wire with meter no signal.
The ground post and ground wire are both the chassis ground, so there is no signal between them.

If you haven't already, you could try floating the turntable ground. But it sounds like the hum is not going to be solved without soldering. Instead, you probably need to pull out the boards and star ground the boards themselves. I would try that before moving the power supply, which has a steel divider to separate the transformer, although moving the AC out might help, too.
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Old 8th June 2020, 01:58 PM   #22
creed2 is offline creed2  United States
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I should have mentioned I have hum without turntable even hooked up in this temporary set up to evaluate problem. I did star ground input/out negitive to chassis with no luck. Why when I touch chassis with my hand hum goes way way down? Can you tell me how to pull the boards to do star ground. Where do I connect wire on boards and where do I ground them to. What is going on with touching my hand to chassis and hum is greatly reduced does that mean I could ground chassis to something other than itself like another component in the rack.
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Old 8th June 2020, 02:24 PM   #23
creed2 is offline creed2  United States
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I just noticed when I touch the positive negative wound wires going to left channel output RCA it gets extremely loud not as much on other 3 input/output RCA jacks wire.
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Old 8th June 2020, 02:32 PM   #24
jackinnj is offline jackinnj  United States
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Pass Labs Pearl Hum advise/help
Everybody needs to get a look at "Grounding and Shielding Techniques in Instrumentation" by Ralph Morrison.

A transformer with a shield is preferred to the ordinary EI or toroid variety.
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Old 8th June 2020, 08:25 PM   #25
creed2 is offline creed2  United States
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My mistake I didn't have table plugged into input. It does not make super loud hum when I touch chassis or input wires anymore since I plugged table into pearl but hum is still there.
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Old 9th June 2020, 05:57 PM   #26
jamayfie is offline jamayfie  United States
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Pass Labs Pearl Hum advise/help
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Originally Posted by creed2 View Post
Can you tell me how to pull the boards to do star ground. Where do I connect wire on boards and where do I ground them to.
You need to access the bottom of the boards. Use a screwdriver and long-nosed pliers to remove the nuts from the top of the boards. Gently lift the boards off the bolts. You may need to disconnect the boards from the power supply (release the screws on the power supply boards) and may need to desolder the RCA jacks if you need to remove the boards completely. But you might be able do all this with the boards still fully wired if you're agile.

On the top of the board, a white line annotated "Connect Grounds here with a soldered wire" connects C15 to a pad near C11. A short wire jumper makes this connection, but on the bottom side of the board. This is the ground point. You want to add a new wire from this point to the ground post. I would avoid the C15 pad because it also connects C15. Leave the jumper in place and solder the new wire to the pad at near C11 along with the jumper (you will need to use a narrow wire to fit two into the pad). Or strip the insulation from the jumper with a razor blade, gently twist the new wire around it, then solder the new wire to it. Connect the new wires from both boards together at the grounding post. Hopefully that will kill the hum.
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Old 11th June 2020, 02:25 AM   #27
hirscwi is offline hirscwi  United States
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Pass Labs Pearl Hum advise/help
Quote:
Originally Posted by jackinnj View Post
Everybody needs to get a look at "Grounding and Shielding Techniques in Instrumentation" by Ralph Morrison.

A transformer with a shield is preferred to the ordinary EI or toroid variety.
Thanks for the tip. Just ordered one.
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Old 11th June 2020, 09:40 PM   #28
creed2 is offline creed2  United States
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Thank you jam for explanation. If you could please tell me if I understand you correctly. I'm very new at this. There is a wire under the board connecting c15 to a pad by c11. Solder one wire per board to that pad by c11 or tap into that wire going from c15 to the pad by c11. Connect each new wire from each board to the ground post mounted on the back of Preamp that the turntable ground wire will be connected to. If I am correct I will open it up this weekend and give it a shot.
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Old 11th June 2020, 09:49 PM   #29
Temaad is offline Temaad  Australia
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Default Take the Trans out of the case

Hi, I had some hum problems with my Pearl, could never fix so I finally let it go. however I made a significant improvement by moving the trans, 2 meters away from the main phono amp board in a separate box. Connected together with a auxiliary cord of cause. You may get a significant reduction I you put your trans in a separate shielded box with long cord. doing the same as I did.
The fact that the hum goes away when power is turned off points to Trans noise.

Cheers
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Old 11th June 2020, 11:34 PM   #30
creed2 is offline creed2  United States
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If you look at pictures of my pearl there is a lot of excess input and output wire, original owner installed left input and output next to each other on one side of amp and right input output on other side which I've never seen done before can any of this be part of problem? Moving power supply outboard would be last resort before giving up if it's not too much trouble.
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