capacitor confusion

Discussion in 'Marshall Amps' started by hotpockitrockit, Feb 17, 2020.

  1. matttornado

    matttornado Well-Known Member

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    I have a 74 also with the cap removed. I often thought about trying a 100pF or 250pF.
     
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  2. neikeel

    neikeel Well-Known Member

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    I personally find anything in the 180 to 1000pF range a bit spiky with a 1M log pot until you get to around 7 on the dial.

    idealy make a cap box with a dual and a dozen values then croc clip the ends in place and work back and forth until you find what works best for you.
     
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  3. AlvisX

    AlvisX Well-Known Member

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    I've never been too fond of the .005uf brite cap
    But again, for me it's the 500pf peak cap over the mixer resistor that makes the thing unbearable .
    A lot of times what'll happen is , I'll take that peak cap off and put that across the pot ,rather than the .005
    Generally , I use somethin between 250pf & 500pf
    My Teles N Strats are twangy and Les Pauls ,fat




    ^ That 's it ,like an outboard Orange FAC
    I find that certain amps like certain values better ...for instance combos VS heads
     
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  4. hotpockitrockit

    hotpockitrockit New Member

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    Where is that located on the pcb??
     
  5. AlvisX

    AlvisX Well-Known Member

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    If you mean the 500pf cap....
    On a pcb amp ,it's next to the 470k mixer resistors IIRC
     
  6. South Park

    South Park Well-Known Member

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    The type and size cap also determines how the the pot responds and how steep it drops off
     
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  7. hotpockitrockit

    hotpockitrockit New Member

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    so, I bought a capacitor kit with caps ranging from 100pf to 10000pf. I tried all caps at "2" (in the ice pick range so I know the cap is doing what it should and the presence and treble all the way up for max ice pick) and input on vol 1 high
    first, I tried the 4700pf cap (stock value) and it didn't sound that bad. so, next I tried a 10000pf just for kicks, and same thing.. not too bad. I noticed the volume with the higher value caps rolls on almost instantly; like no gain to a lot of gain.
    next, I tried a 681pf and it was ICE PICK! allll the treble .
    next up, 100pf (a fan favorite on the forums) and it didn't sound that great.
    330pf was next, and it too was too bright. (as a reference I would play back to back without the cap to "cleanse my ear palate"
    1000pf was up next and it also was too trebly.
    2200pf was a little better, somewhat bright
    220pf was up next, and sounded ok.

    I then went back to 4700pf to compare and did a back to back with and without it. without it was a smoother distortion and less gain for the same volume (2). when volume was at or above 6.5/7 there was a lot more low frequencies, when vol was rolled back (cap in place) it didn't affect the distortion as much as the lower frequencies rolled off.

    is this a similar experience with you guys??
     
  8. hotpockitrockit

    hotpockitrockit New Member

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    did some experimenting today
     
  9. hotpockitrockit

    hotpockitrockit New Member

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    just did that! works great
     
  10. mickeydg5

    mickeydg5 Well-Known Member

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    Fender used 100pF in Bassman amplifiers. Marshall used the same in early amplifiers.
    Anything close to that should be similar.
    Marshall used 4700pF or 5000pf (.005uF) later on which is a lot and brings on a lot of signal at low volume settings as you noticed.
    Anything above that is almost like shorting the top half of the volume potentiometer in these amplifiers.

    The function of the "bright capacitor" is to provide some brightness at low volume settings on the potentiometer control.
     
  11. hotpockitrockit

    hotpockitrockit New Member

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    like a treble bleed on a guitar
    why is it that 5000pf had less harshness than 681pf?
     
  12. mickeydg5

    mickeydg5 Well-Known Member

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    First, what is the brand and model of both the 5000pF and the 681pF?
    Second, how were all of the amplifier's controls set?
     
  13. hotpockitrockit

    hotpockitrockit New Member

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    I used a high voltage ceramic disk, and after tweaking a bunch I now see why it seemed that way.. with the higher values, it lets a lot more signal through a lot faster. I ended up choosing a 100pf as it kept some of the character of the .005, and not too much high end
     
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  14. mickeydg5

    mickeydg5 Well-Known Member

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    Exactly why Fender used that value and why so many turn to similar values for that job. :yesway:
     

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