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I am trying to figure out why a loud sweeping sound comes out of my left speaker when the PEC 100k dual pot is turned w/ or without music on in my 27 pre. Have I cooked the pot.? It was a slightly used one from my closet from other projects. Right channel is just fine. The sweeping, swooshing sound is loud when controle is turned & it is the entire range from 6:00am to 6:00pm..I have had this happen to me before, but for the life of me can't remeber what it was. I have wood chassis w/ ground buss. Smoked controle or ground problem.?
Follow Ups:
Problem solved... I installed a black 100k Alps with test clips & noise all gone, so swapped out the PEC. Now all is good. The PEC got crazy noisy on 1 channel only. I am not so happy about using them anymore.. I have some PEC's for my 26 build. I'll try em one more time..but that will be that. If they go also, I am done with PEC. Maybe I got a large dose of DC on it way back when, I can't remeber, I have done some very crazy & stupid experiements, so it is very possible I did the damage. For a mil spec pot, it sure is wierd..
It's possible the PECO pot is the cause, but it is sealed up so it means it's less likely than a pot open to contamination.The DC on the pot problem is another strong possibility.
FWIW, you can dissemble and clean the PECO pots, but you need to be real careful. And DeOxit D5 works just fine on pots too. Mike Samra says be sure it's used in a ventilated area, and that's good advice about ANY cleaning product for any job. IIRC, the carrier in DeOxit is naptha, and naptha can get to you. Use D5, use it with some ventilation, and you'll have no problems - I've used it successfully for many years.
I had just posted this issue you are having and I dont think cleaning will fix it but it may..Ian guessed what it is most likely and that is DC offset caused from a leaky coupling cap or caps.What happens is Dc spikes the grid of the preamp tubes and that causes oscillations and noise and a host of other problems..Its only in one channel I think and usually when that trouble hits with a dirty volume control,it happens in both channels.Not always but usually.Id say you have a leaky coupling cap.Also control cleaning you want to use deoxit calilube and and if you use the deoxit 5,use it only on switches and use it in a well ventilated area.
Leaving the connections to the source as they are, if you switch interconnects at the input to the pre end only does the noise change channels?
I'm wondering about DC offset. When I had that problem it was from DC going through the pot. I think some kinds of RF oscillation can cause that too but I don't have any experience with it myself. Do you have a grid stopper on the 27?
You know what ..? It could be my Mac 74 Tuner, I don't recall this problem with my DAC.I'll do a quick swap. I do not know what a grid stopper is, this is my 1st scratch build. The 27. I just have the 100k pot to pin 3 & a 22k 1w resistor to pin 2 & battery bias NiMH pin 4. I probably really fried the damn pot cuz I tried soldering a ground wire the case I could NOT do it, evev with a 40 watt gun. So I attached it under the washer in a sneaky can't see fashion. I have wood chassis , so I thought just maybe pot case needed grounded. It is grounded now, & might be helping some.I think it might be dc offset from the Mac 74 tuner. Didn't even think of that.I been having so much fun with FM mono I didn't think to change sources..The PEC pot seems fine after the fry session with soldering gun, but still has sweeping soud with Tuner. I will change sources. The PEc's are mil spec & suspect I should not have a dirty pot, as it is sealed & never had a PEC go bad..? built like tanks.
Probably just dirty. I don't know if these are sealed or not, but if not you can try some deoxit.
it might be a good idea to read Michael Samra's thread linked below
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