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Pass Labs Pearl Hum advise/help
Pass Labs Pearl Hum advise/help
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Old 28th June 2020, 04:26 AM   #41
Ben Mah is offline Ben Mah  Canada
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Pass Labs Pearl Hum advise/help
It is better keep the input wires together and the output wires together to minimize loop areas. For the output wires, keep the twisted left and twisted right wires together from the board output to the RCA jacks.

http://hifisonix.com/wordpress/wp-co...ound-Loops.pdf

This is an informative article on Ground loops. It is aimed towards power amplifiers but the principles apply to preamps too. Loop area is discussed and there are practical tips at the end, including examples of loop area.
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Old 28th June 2020, 04:49 AM   #42
creed2 is offline creed2  United States
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Will blue and yellow power supply wires cause a problem passing by the input and output wires and rca's as you can see in picture? With there length being as they are that is the only way I can route them unless I add more wire and run them away from rca's and run them behind boards or along front face plate.
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Old 28th June 2020, 05:22 AM   #43
Ben Mah is offline Ben Mah  Canada
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Pass Labs Pearl Hum advise/help
The DC power supply wires crossing the signal wires should not be a problem. See page 63 of the article that I referenced which shows signal wires and DC power wires in close proximity. It actually minimizes loop area.

AC wires and transformer close to signal wires and circuitry are problematic.

Also note that sometimes the orientation of the toroid transformer may affect noise. Rotate to find minimum noise orientation. Also use your ohmmeter to make sure that the ground of the RCA jacks are not in contact with the chassis.
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Old 28th June 2020, 03:29 PM   #44
creed2 is offline creed2  United States
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Boards are drilled and mounted just need to solder back. Do I need to use star ground from ground wire under board or star ground fron RCA negative inputs like before trying to stop noise? Ben Mah when I put volt meter on negative of RCA jack and preamp chassis it is making a connection. What problem can this cause noise? What is best way to stop contact if that's what needs to be done?
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Old 28th June 2020, 09:40 PM   #45
Ben Mah is offline Ben Mah  Canada
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Pass Labs Pearl Hum advise/help
The RCA wires should connect to the boards as shown in 6L6's build guide:

Pearl (one) Build

As far as the RCA jacks, check continuity before wiring them up. With no connections, the RCA jack ground should not have continuity with the chassis. There should be plastic washers on both sides of the chassis to insulate the RCA jacks from the chassis.

As for grounding to chassis, please check 6l6's build guide, and perhaps others can help you. I do not have a Pearl so I do not have any direct experience.
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Old 29th June 2020, 02:12 PM   #46
creed2 is offline creed2  United States
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Hum is greatly reduced, at volume at 50% you need to put your ear up against speaker to hear hum. Before at 30% you could hear it at 6 feet away. After switching power on one side of box left channel had no hum but right still did so I reconnected star ground from bottom of board and hum disappeared. I'm just wondering if reconnecting star ground off of negative RCA jacks might make it even quieter. I'm still considering moving power supply to its own box to maybe get that last bit of hum out. Thanks everyone for there time and effort helping me reduce hum could not have done it without everyone's help, this is really a great place for someone like me getting there feet wet in DIY electronics, thanks again everyone.
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Old 29th June 2020, 02:27 PM   #47
mhenschel is offline mhenschel  Canada
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That's great.
I'm planning a remote PSU for my Pearl build. I think it's the right approach.

Pics?
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Old 29th June 2020, 02:34 PM   #48
Ben Mah is offline Ben Mah  Canada
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Pass Labs Pearl Hum advise/help
creed2
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Old 29th June 2020, 02:53 PM   #49
mhenschel is offline mhenschel  Canada
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@ben mah
Thanks for ground loop presentation. Good stuff.

I had two questions:
On page 63 would the loop area be better or worse if the transformer and rectifier section were flipped (ie like my Hafler DH-200)?

On page 71 I'm not sure why the turntable is not in the loop area like it was in the diagram on the previous page. Or, conversely, why the loop between AC cords to the preamp and power amp remain.
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Old 29th June 2020, 03:24 PM   #50
Ben Mah is offline Ben Mah  Canada
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Pass Labs Pearl Hum advise/help
page 63: Transformer at the front and power supply at the back is the usual arrangement for First Watt amps. I believe that this arrangement has advantages. It keeps the transformer away from the back of the amp where low level audio signals enter. Transformers emit strong magnetic forces that are bad for audio. AC wires are bad too so they should enter at the middle of the case in stereo amps and kept to the centre of the case on its way to the transformer.

page 71: I believe you are correct. The loop area should still be there, albeit much smaller. The thing to do is to group the AC cords together as much as possible.
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