Pot values original spec or...

Discussion in 'The Workbench' started by Seanxk, Oct 25, 2020.

  1. Seanxk

    Seanxk Well-Known Member

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    I have just changed both ch1 & ch2 volume pots on my road worn SB 100, they were measuring 1.6M & 2M and a little notched and noisy in operation.
    About 10 years ago I took them apart as the tracks were nearly worn through, I tweaked the wipers to run a few thou off the wear and thought well all is good and I will replace them one day soon. Now the day comes, I have two good pots that measure 970K the tracks are near identical in taper %, so in they go, they are smooth quiet and really positive but I seem to have lost some depth, some chewyness?.
    So my question is, what does increasing or reducing the ohmage on the volume pot do, have I increased the gain going back to specs or lost some low freq?, I really can't tell but all seems a bit thin.

    Any thoughts much appreciated.
     
  2. thetragichero

    thetragichero Well-Known Member

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    without a schematic one may never know
     
  3. South Park

    South Park Well-Known Member

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    Get the schematic and replace with the exact ones. The signal loss is what you are dealing with .
     
  4. neikeel

    neikeel Well-Known Member

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    As per my previous posts on the subject and research by others, slightly high testing pots seem to sound better esp the early AB types.
    There was plenty of discussion/trial and error on Metroamp years ago that came to this conclusion. I wish I could explain exactly why !
     
  5. thetragichero

    thetragichero Well-Known Member

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    higher value pot means there's more resistance to ground and (slightly) less loading, no?
     
  6. Seanxk

    Seanxk Well-Known Member

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    Last edited: Oct 26, 2020
  7. Seanxk

    Seanxk Well-Known Member

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    Ok, tracks removed again and this time I increased the ohms to 1.5M for each pot, re installed in the pot bodies and back in the amp, the mojo is back, don't know what it is but it seems chewy again.

    I increased the track ohmage by polishing ( jewelers rouge ), didn't fancy the scraping method. Did it face down on a rag on a flat surface, then isopropyl wash and check, continue polish & wash until desired reading.

    For ref, ch1 & ch2 are now 1.5M, and original readings for, treble 333K, mid 30K, bass 1.25M, pres 5.6K
     
  8. neikeel

    neikeel Well-Known Member

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    Sounds about right.
     
  9. Seanxk

    Seanxk Well-Known Member

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    Drifting with soul, classic Marshall
     

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