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Pots - 500k vs 1 meg....

Discussion in 'Pickups & Electronics [BG]' started by Cieran, Apr 14, 2010.


  1. Cieran

    Cieran

    Aug 24, 2009
    UK
    Am i right in thinking that a 1 meg pot (audio/log) will act the same as a 500k pot when turned down 1/2 way? By the same token would this mean that the same 1 meg pot will act the same as a 250k pot when turned down 3/4 of the way?

    From what i understand from line6man in another post:

    "When you turn your volume knob all the way up, there is no resistance from input to output, but there is a resistance from your signal to ground. So even with a pot all the way up, some of your signal will still bleed off to ground, and cause you to lose some of your brightness. The greater the resistance, the less of your signal bleeds thru to ground, so thats why a higher value pot has a brighter tone."

    Is my understanding correct?
     
  2. With an audio taper 1M pot, 500K should be around 4/5 of the rotation, not halfway.

    You aren't accounting for the resistance series to the signal.
    If you turn a 1M pot down to 500K, that's a 500K resistance to ground, but also a 500K resistance between the input and output that would not exist on a 500K pot turned all the way up.
     
  3. Cieran

    Cieran

    Aug 24, 2009
    UK
    Thanks line6man - as informative as ever. I did actually mean a linear pot but wrote audio by mistake. Presumably this would make it a 1/2 turn as i originally proposed?

    In regards to input/output & signal/ground - if i were to turn a 1meg pot to half way (effectively creating a 500k resistance) would this have the same tone/volume as a 500k pot turned all the way up with 0 resistance?
     
  4. Yes, with a linear taper pot, 50% rotation equals 50% resistance, so halfway is 500K.

    No, it wouldn't have the same volume as a 500K pot on full.
    It would be the equivalent to running a 500K pot on full, with a 500K resistor between the pickup and the input of the pot.
     
  5. Cieran

    Cieran

    Aug 24, 2009
    UK
    Ahhh ok. The reason i ask is that I have hooked up my Gretsch G2202 (1 x humbucker) with a 1 meg volume pot which definitely made an improvement as it was very quiet, but when it came to the tone pot i was undecided between a 500k or 1 meg. I am fairly new to all this so it was hard for me to tell the difference in sound.

    In the end i settled for a 1 meg tone pot as it was a quite muddy sounding bass (due to it's short scale) and i assumed that if i found it too bright i could always turn the tone down to resemble something like a 500k pot. That was my logic anyway coming from the perspective of a newbie.

    I know this sort of thing is subjective but do you think this was the best thing to do - all things considered? Or is there another better way i could have gone about things?

    Thanks
     
  6. Well, if you're talking about a tone control, a 1M pot turned down to 500K is the same thing as a 500K pot on full, because the pot is only being used as a variable resistor between the capacitor and ground. The third terminal is open.

    However, 1M is quite bright for a tone control, especially considering that linear taper pots don't work well as tone controls. They have little effect until toward the end of the rotation.
    I would imagine a 1M tone control to be fairly useless throughout most of it's rotation, regardless of the taper. Was this the behavior you observed with the tone control, or have you not installed it yet?

    Have you considered a bypassable tone control instead?
     
  7. Cieran

    Cieran

    Aug 24, 2009
    UK
    I originally set myself up with 500k audio & linear pots as well as 1 meg audio & linear - i didn't go any lower as the stock pots were 500k and it already sounded quite muddy. I then went about testing using alligator clips and tried these combinations:

    500k/500k
    1meg/500k
    500k/1meg
    1meg/1meg

    Eventually i came to the conclusion that either the 1meg/500k or 1meg/1meg combination sounded best - tho the 1meg/1meg option sounded the least muddy. I also decided that linear sounded better for volume and audio for tone - although i managed to fry my only 1meg linear pot when soldering so had to use a 1meg audio pot for the volume instead.

    The taper of the 1 meg audio tone pot isn't as bad as you would think. I tend to prefer the tone pretty much exclusively between 7-10 on this bass so it works for me.

    It was realy a case of trial and error and alot of patience with the testing to get to this current setup - i found that because of the single humbucker it tended to sound quite muddy which is why i tried to compensate with the higher value pots.

    What is a bypassable tone control? Is that where you leave the tone pot out of the equation so the signal has no tonal resistance?
     
    Killed_by_Death likes this.
  8. A bypassable tone control would be a tone control with a switch to remove it from the circuit.

    Fender makes a 250K pot with a switch at the end of the rotation that "clicks" off.
    Or, you can use a push/pull pot to bypass the control when you pull up on the tone knob.
     
  9. Cieran

    Cieran

    Aug 24, 2009
    UK
    Thanks for the info - much appreciated.

    I only finished soldering the electronics 4 days ago so i will see how i get on with it for a while before i decide to add any further mods. Good to know i have other options.....

    Cheers
     

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