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In Reply to: RE: PAS-3 right channel hum posted by petercapo on January 17, 2017 at 16:22:37
So would the goal of these changes be to even the hum out to both channels or eliminate it?
And when you say move the wire from the top of 8 to the top of 1, do you mean underneath 1, where there are 3 wires already connected?
I can open it back up and see where the wires underneath go to.
Follow Ups:
As I mentioned, you have [apparently] undocumented changes to your PAS. It is not in the original configuration, which can present additional challenges for remote troubleshooting.The changes I suggested would be an attempt at making the hum more even in both channels, along the lines of the old post with Bill Thomas. My procedure is a little different from what Bill did, but it is also consistent with a change I see in the development of the PAS manual over the years that I think may have been implemented to deal with this very problem.
If the way I am suggesting doesn't work, then you can try to do it more closely to the way Bill Thomas described, though it might be more involved. Part of the reason why I am suggesting my particular way of doing it is because it should be relatively straightforward.
However, given the way your PAS is currently wired, all bets are off. In other words, there's no guarantee that either way will work, though one might. Hence, I recommended that you take note of the changes you make so that you can put things back to how they were, if necessary.
To achieve a more overall reduction of the hum [in both channels] would be more involved.
When I suggested moving the wire at the top of 8 to the top of 1, I meant just that. You have to be careful, because the bottom of 1 has other wires soldered to it - you don't want them to become disconnected. I understand that this is may be somewhat challenging. If you find it easier to run the wire to the underside to connect to 1, then go ahead. Just make sure that there are no shorts to adjacent circuitry.
Edits: 01/17/17 01/17/17 01/17/17
Well, I dropped the unit back off at the local guy who took a crack at the PAS earlier with your recommendation as well as the one from Bob years ago. He's going to give them both a try and see if either work.
Let me ask you this: would changing the PC5 board make a difference? Like maybe upgrade/change to Tube Nirvana Z-Mod or the PAS3 Aikido?
If your tech is going to be diving into it, he might want to think about eliminating what appear to be a number of ground wires that might not be necessary. It might not be possible to implement Bill Thomas' fix the way he did if you have more ground wires than he did. This is another reason why I wanted to offer you a simpler approach with moving just the one wire (and also removing the wire from eyelet 8). Of course, my idea might not help depending on all the other stuff going on in your preamp.I suggest you get your tech a copy of an original Dynaco PAS manual along with its corresponding pictorial diagrams. With regard to ground wiring, I suggest a later PAS manual, such as for the PAS-3X, though it may not be appropriate for certain other aspects of troubleshooting, especially since your PAS is not in any standard Dynaco configuration.
With regard to changing to a different PC board... keep in mind that with the nonstandard and possibly redundant grounding scheme you have now (that could be causing ground loops), your existing line board isn't really getting a fair chance. That's not the original line board, anyway. It is a newer, fiberglass board, so it has already been changed-out. It's the ground wiring that is causing your hum problems. Switching to a different circuit board design may or may not help the hum, depending on how it integrates into your existing grounding system of wires.
I offered the suggestions that I have in the hope that it might alleviate the hum imbalance. But, what your PAS really needs is a complete reworking of the grounding by someone who is very familiar with both the original PAS and the grounding needs you now have with the tubenirvana cap board. If it were my PAS, I'd just remove every ground wire there is and start from scratch.
Edits: 01/18/17 01/18/17
I've sent all of this to my tech, so we'll see what he comes up with. He's a sharp dude, so I'm hopeful.
About that wire at 8... I suggested removing it because there ought to be a different wire grounding the tubenirvana cap board more directly to the chassis. But, if there isn't, then you might need to keep the wire at #8. Again, perhaps not the best way to do things, but we're trying to find something that might help short of tearing the whole grounding system apart.
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