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Post by thedoc735 on Jul 30, 2020 17:13:41 GMT -5
OK, So, yesterday I replaced a volume pot with a Vintage Inspired pot which cost A LOT of cash for international delivery + customs/import charges! (to UK) …
It worked great first day! - …but now (day two), it is very scratchy with interference! When I wriggle/rattle the shaft (which has a slight amount of ‘play’) the volume jumps up and down very noticeably! Also, if we call zero as silent and 10 as maximum volume; at 0.5 the volume goes silent but then as it is reduced to ‘0’ it comes back ON to about ‘1’? At the other end it reaches max. vol. at about 9.5 but then at ‘10’ the volume drops off to about ‘3’ish?
Any ideas please?
On day two I had slackened off the retaining nut and later forgot to re-tighten it securely! The control cavity is shielded with black carbon paint and grounded to earth! Would that make a difference to the volume pots performance as the pot has its own grounding from its casing to earth? i.e. poor/intermittent control cavity contact?
Many thanks!
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Post by JohnH on Jul 30, 2020 17:27:48 GMT -5
Unless 'Vintage Inspired' means designed to replicate a scratchy worn-out old pot from a 1950's radiogram, Id suggest to look for any solder joint on the pot that may be not quite good, like its maybe acting intermittently, or maybe some whisker of wire getting over to the grounded paint or another wire.
You can also learn a lot from measuring resistance of the whole guitar while sweeping the volume pot. Set meter to 200k scale, clipped with the meter wires onto tip and barrel of a guitar cord, then select a pickup and sweep the volume from max to min.
At max, it should read a few k, being the pickup resistance. As you turn down, it should rise to 1/4 of the volume pot resistance (actually 1/4 of pot plus pickup), like around 130k for a 500k pot, This happens at around 6 on 7 on a log pot. Then as you go lower, it should reduce to zero. (side note: this is also a great way to figure out the pickups and volume pot on an unknown guitar)
But if it doesn't happen like that, it gives a clue, maybe it goes off scale, indicating a disconnection, or maybe a zero indicating a short somewhere.
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Post by thedoc735 on Jul 31, 2020 11:29:15 GMT -5
Unless 'Vintage Inspired' means designed to replicate a scratchy worn-out old pot from a 1950's radiogram, Id suggest to look for any solder joint on the pot that may be not quite good, like its maybe acting intermittently, or maybe some whisker of wire getting over to the grounded paint or another wire. You can also learn a lot from measuring resistance of the whole guitar while sweeping the volume pot. Set meter to 200k scale, clipped with the meter wires onto tip and barrel of a guitar cord, then select a pickup and sweep the volume from max to min. At max, it should read a few k, being the pickup resistance. As you turn down, it should rise to 1/4 of the volume pot resistance (actually 1/4 of pot plus pickup), like around 130k for a 500k pot, This happens at around 6 on 7 on a log pot. Then as you go lower, it should reduce to zero. (side note: this is also a great way to figure out the pickups and volume pot on an unknown guitar) But if it doesn't happen like that, it gives a clue, maybe it goes off scale, indicating a disconnection, or maybe a zero indicating a short somewhere. Recap: first day the pot worked fine, the second day it didn't! I said I had slackened of the retaining nut to do a little job but forgot to re-tighten it afterwards! The control cavity is 'active' for ground shielding and I wondered if the intermittent contact between the pot and the cavity could result in weird behaviour? Well, without doing any of what you suggested above (so far), I nipped up the pot's nut securely and squirted a little studio fader DeoxIT into the pot, and guess what(?) - it works great again! There were no bad solder joints anyway. So, odd behaviour solved for now! And the above advice may serve me and others in the future. Many thanks! |
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