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.
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.
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.
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.
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.
Separating left channel from right and input from output would seem prudent in any event. You might look at shortening the twisted pairs, but first just try dressing the wires such that you have some separation and see what that does.
Connecting the board grounds to the ground post would be next. See how that does.
Oh and check the wire from the post to the chassis too.
On the power side of the unit I wonder if it might be possible to move the power wiring away from the dividing wall to separate AC from signal as much as possible?
And that dividing wall... it should be grounded to the rest of the chassis too I believe.
Good luck. I'm just getting going with my Pearl-1 build and I look forward to your success!
Connecting the board grounds to the ground post would be next. See how that does.
Oh and check the wire from the post to the chassis too.
On the power side of the unit I wonder if it might be possible to move the power wiring away from the dividing wall to separate AC from signal as much as possible?
And that dividing wall... it should be grounded to the rest of the chassis too I believe.
Good luck. I'm just getting going with my Pearl-1 build and I look forward to your success!
Yes, correct on the ground wiring.
As for the input/output wires, they could be shortened and/or possibly twisted more. I've been told the left and right channel wires should be the same length, but I'm not sure that's true. If you wanted to drill new RCA holes, you could make the wires really short, but I find the flexibility of a little extra wire helpful when I need to make changes. You can also route the wires through wire clips to keep them tight to the chassis. I usually do this, but find the adhesive type clips lose their stickiness pretty quickly and end up rattling around in the chassis.
In addition to all of the grounding suggestions by others, another change that will help reduce noise further is to rearrange the boards. Proximity to AC and transformer is always a problem, and more so with low level signals.
Presently your left board and its output is right next to the AC input and very close to the transformer. If you rotate the boards and relocate the power supply board as shown on your picture that I have drawn on, that will provide a bit more distance between the transformer/power supply and signal boards. Also, keep both low level left and right signal inputs to the extreme right side of the case would be helpful, and orient the boards with the input towards the back.
Presently your left board and its output is right next to the AC input and very close to the transformer. If you rotate the boards and relocate the power supply board as shown on your picture that I have drawn on, that will provide a bit more distance between the transformer/power supply and signal boards. Also, keep both low level left and right signal inputs to the extreme right side of the case would be helpful, and orient the boards with the input towards the back.
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I'm going to go ahead and move boards suggested by Ben Mah since board will be raised to add more ground suggested by jamayfie. I want to thank everyone for trying to help me with hum problem. Maybe this will help other people in the future with same problem. This preamp sounds to good to give up so soon. Hopefully there is enough existing wire to move boards without having to order more.
Been a little busy but going to open it up this weekend. I'm going to tap into boards for star ground and move power supply board to transformer side of chassis. If you look at pictures the power switch would be left on the side with signal boards after mod. Should I move that on transformer side or does it matter? Are there any power supply wires that need to be separated from one another on power supply side? If I'm understanding mount or point the input part of the boards closest to RCA jacks. Thanks for all help a couple weeks ago I will let everyone know if this does the trick this weekend.
Before moving boards I tried tighter wounded input wires. Put star ground coming from stock wire under board to phono ground jack. Even tried star ground again coming from negative on all RCA jacks going to chassis ground in conjunction with under board star ground. With moving power supply I believe I can do it without adding wires and just move transformer to blank spot and power supply boards to transformer spot or is that a mistake causing more of a noise problem. Easiest way to move all power to one side. Or should I leave transformer alone and add wire to move power supply boards? Looks like this last option before outboard power supply, is that correct, thanks everyone for hanging with me on this hum problem.
I moved boards around and will drill and raise boards tomorrow and wire everything back. Left channel power supply wire is long enough so I don't have to move transformer. I marked the input and output so you can see how I acquired Preamp, everything lines up but input and output rca's will be side by side. Should I lengthen left channel input wire so input rca's are on one side of amp and output left and right are grouped on other side of amp.
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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-content/uploads/2019/02/Ground-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.
http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-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.