No more 60 Hz hum in a PL2000 preamp.

Joe, yes indeed, and I find it annoying that the values are so far off. I understand it can be dialed in, still, seems it should be more accurate. Anyhow, I have a couple of those cheap 24 step 50k attenuators with Dale resistors ordered from China. Will give those a try. Appears they even have the correct shaft and will fit. We'll see.
Work week begins tomorrow. Later!
 
Wouldnt take long at2.50 a pop for those IRC's to get a pricey attentuator. Course the last time I priced the Alps pot used in a Spec 1 it was north of 475.00....
 
Gepetto said:
That's why the 2000 has a balance pot George :)
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Joe, another pearl of wisdom from you!
I couldn't see it!
The balance pot fine tunes the volume pot!
So, I have a dual channel signal generator and a dual channel scope. On the bench, the preamp can be fine tuned for perfect output balance.
Then the balance pot can be tightened down for accurate indexing. That's why they mounted it with pigtails rather than directly to the board!
As long as the scope shows even waveforms at 1/4, 1/2, 3/4 volume, it's good. The carbon tracks of the dual pots don't need to be absolutely equal.
 
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George S. said:
Joe, another pearl of wisdom from you!
I couldn't see it!
The balance pot fine tunes the volume pot!
So, I have a dual channel signal generator and a dual channel scope. On the bench, the preamp can be fine tuned for perfect output balance.
Then the balance pot can be tightened down for accurate indexing. That's why the mounted it with pigtails rather than directly to the board!
As long as the scope shows even waveforms at 1/4, 1/2, 3/4 volume, it's good. The carbon tracks of the dual pots don't need to be absolutely equal.
Click to expand...
Glad that I connected some neurons for you George... :-)
 
laatsch55 said:
Wouldnt take long at2.50 a pop for those IRC's to get a pricey attentuator. Course the last time I priced the Alps pot used in a Spec 1 it was north of 475.00....
Click to expand...
Don't even wanna know the price of the pots for my Pioneer D23 if i can get them.
 

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So, what did I find really bad in the CTS balance and volume pots beside dirt and green copper (sulphate?) on the contacts? The wiper slip rings have deposits that alcohol will not remove, and they need to be absolutely clean before lubing them, the carbon tracks, the contacts, and shaft and barrel with DeoxIT DFG-213 grease.
Tried a Dremel nylon brush wheel, soft brass brush wheel, and settled on a well used steel brush wheel carefully used to polish the deposits off what appears to be silver plating.
Low speed setting, careful use in regard to plating and potentially snagging a contact, and they're clean and polished.
These were extra, unused pots. I'll do the pots in my two PL 2000 S2 preamps in use. Take noise measurements, then install the 24 step attenuators, and take additional noise measurements for comparison, and see if there's any difference.
 

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The 50K Ladder pots arrived. They look very good on the ohm meters in regard to resistance matching.
The "D" shaft stub will need shortened and the flat "flattened" slightly more. Should be a very good fit.
Going to be awhile before I get them installed.
 

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My 2000s2 Z3 went bad causing my hum recapped only way I could get rid of it was with that birddog thing you talked about stock z3 all had same problem so the birddog solved my hum.
 
GaryCooper said:
My 2000s2 Z3 went bad causing my hum recapped only way I could get rid of it was with that birddog thing you talked about stock z3 all had same problem so the birddog solved my hum.
Click to expand...
Ah yes, the BrownDog adapter. Thanks to Lee and Joe for turning me on to those, they're great!
Watch this thread as I have a pile of bypass caps to test on those BrownDogs. (If I ever get any free time!)
Gary, I'm glad your repairing and enjoying your PL gear. Excellent!
 
Going to open the Alps tone pots and clean and grease them. Then install the 50K volume and balance ladder pots.
 

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The 100K Alps tone potts have limited serviceability unfortunately. Staked construction and unable to disassemble them further.
Alcohol bath and careful greasing will be all I can do with these.
 

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Got the Alps tone pots done. The look really good on the ohm meter.
Going to disassemble, clean, and grease a extra switch pack I have. I'll soak strips of coffee filter paper in DeoxIT and pull them thru the contacts.
Will try to polish those chromed plastic buttons.
 

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The ladder pots barrel is slightly smaller than the original, but fits well. The D shaft needs shortened and flat depth added. Not bad, considering all.
 

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