Bass rolloff cap

Discussion in 'The Pickup Place' started by Rockhead, Sep 18, 2020.

  1. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    Bass rolloff2.jpg
    Hello. I have a 5220 with the Brodtrons Pups. Love the bridge, hate the neck! I have the neck pup as low as possible which is about even with pickup ring but it is still too muddy with even the slightest overdrive. I've tried adjusting the pole pieces to no avail! Anyway, one of the suggestions is to put a "Bass rolloff" cap in series with the pickup. Is this drawing correct or do I need to put it between the switch and and the input of the Neck volume pot?

    Also, you may have noticed that the Master Tone pot is not connected to the output jack as per the normal tone pot circuit but it feeds the Master Volume which in turn is connected to the jack. I've seen this wiring here a while ago. It makes sense to me but am wondering if it would alter the sound for better or worse. Would this help with the muddy neck?

    Appreciate any insight,
    Thanks!
     
  2. drrohle

    drrohle Synchromatic

    804
    Jan 3, 2014
    Hays, KS
    Did you try raising the pup height? If it's as far away as you are saying, it will make the "muddiness" worse. Try bringing the whole pup height up some but not so close as to hit the strings with the pole pieces as you fret the last one.
     
  3. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    Yes. I have adjusted the pup height from high to low. It was more muddy when I had it close to the strings.
    The Low E and D strings are the worst offenders. Even with a little overdrive theses strings are VERY dark sounding. I have adjusted pole pieces and pup heights. Just want to now if the schematic diagram is kosher.

    Thanks!
     
  4. hcsterg

    hcsterg Friend of Fred

    Feb 13, 2012
    France
    @Rockhead ,

    Looking to your stamp-sized picture :eek: as far as I can read it :confused:, I'd say yes : you placed the HPF (High Pass Filter) cap at the right place for your neck PU.

    You will have to search the correct value for that HPF cap, given that :

    Fc=1/(2.Pi.R.C)

    where Fc is frequency cutoff in Hz, C is HPF cap in Farads, and R the pot resistance in Ohms. So as R will vary according to the PU volume pot, it will affect Fc, increasing it (less bass) when you lower the PU volume.

    How much ?

    It's a 6dB/oct. slope filter (in theory) and I wouldn't be surprised if you had to go for quite small values HPF caps... Let's consider for example only 0.003µF (= 3000pF) with the PU volume pot maxed (= at 500K) :

    Fc = 1 / (6,28.500 000.0,003.10E-6) = 107Hz.

    Meaning that the HPF cutoff point at -6dB is located at 107Hz.

    Is it enough ? Or too much ?

    I'd say that it is not a silly value to cut the muddy bass on light overdrives without killing the tone of the pickup, but you must test to confirm or tweak the value, and decide what's best for you, according to the use of your instrument... :)

    If you want a steeper slope, you can double the filter (adding a second cell) : you'll reach then 12dB/oct, the frequency being the same.

    Good luck ! ;)

    A+!
     
    Last edited: Sep 18, 2020
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  5. jarrodtaylor

    jarrodtaylor Gretschie

    383
    Mar 14, 2019
    Delray Beach, FL
    I usually wire them after the volume but it'll cut the low end on either side (master bass cut would happen after individual pickup volume anyway).

    Bass cuts are an interesting mod on guitars. Here's what I've found from experimenting:

    - Like @hcsterg said, use the right cap value. Something like .002uF and not .02uF. Since you won't be wiring the cap to ground, it's easy enough to try different values.

    - 1 Meg reverse audio taper pots seem to work best. I've tried 250k and 500k, linear and audio tapers, none of them work as well. I get them from G&L here: https://g-l-online-store.myshopify.com/collections/electronics/products/split-shaft-potentiometer

    - If you haven't played a bass cut before don't expect it to be a night and day difference. It'll add clarity by thinning out your sound but keep in mind your lows aren't the only thing overdriving.

    Sounds like that'd just make your master tone and volume interact differently.

    Those pickups shouldn't be all that muddy and definitely shouldn't be that low. Filters usually work best right up by the strings. Which pots are you using?

    Also, adjusting pole pieces is useful for balancing strings but that's about it.
     
  6. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    Thank you HC and Jarrod! Sorry for the tiny photo. I wasn't sure what value cap to use. I just copied what was in the schematic. Do you think there could be something wrong with the guitars wiring? I can't imagine it being normal but that does seem to be the complaint with the Brodtron neck pup in the 5220. The bridge on the other hand sounds great. Go figure.

    I did think about using a 1 meg pot for the neck volume but I thought it would make it worse since it would increase volume. Is that correct? I'll order some caps and see how that works just because it's easy but I will consider replacing the pot depending on how the caps work out.

    Thanks again :)
     
  7. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    The neck and bridge volume pots are whatever came with the guitar. I did change the master volume with a CTS audio taper, 500K.
     
  8. jarrodtaylor

    jarrodtaylor Gretschie

    383
    Mar 14, 2019
    Delray Beach, FL
    1 Meg would be for the bass cut.

    The volume should be 500k. 250k would sound dark, which is why I was asking. A higher pot value won’t be noticeably louder. It’ll be brighter.

    It really sounds like you have a 250k volume pot on your neck pickup. Could just be a crap part. I’d order a 500k audio taper pot and try that first, with the pickup back to normal height, before adding a bass cut.

    The Emerson Pro CTS pots are excellent. IIRC, CTS pots are usually +/-20% of their stated value and resellers can do custom runs with tighter tolerances. Emerson and Mojotone do that and will be closer to the stated 500k. If the guitar came with crap pots I wouldn’t be surprised to find your neck volume at closer to 300k. Or maybe because the Broadtrons are kinda sorta targeting Gibson players they could’ve intentionally used darker pots.
     
  9. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    I just ordered 2 Bournes 500k reverse taper audio pots from mouser for bridge and neck volume. I'll probably replace the tone control as well. I also ordered 24 awg 2 conductor shielded cable and just rewire the guitar while I'm at it!
     
  10. Henry

    Henry I Bleed Orange

    Apr 9, 2014
    Petaluma
    You can also try removing some of the pole pieces.
     
  11. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    which row? closer to the neck or bridge?
     
    Henry likes this.
  12. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    would replacing thetone pot with a 1 meg make any difference on the neck?
     
  13. jarrodtaylor

    jarrodtaylor Gretschie

    383
    Mar 14, 2019
    Delray Beach, FL
    Seems like the neck side would be more bass heavy.

    Possibly? A 1 Meg reverse audio taper pot works well for me specifically for a bass cut. It provides the best usable taper and range that I’ve found and doesn’t noticeably change the highs. But that’s a different thing than a normal tone pot that cuts highs. A no load pot, or simply taking the tone pot out of the circuit, would help eliminate the master tone as a possible culprit.

    Higher value pots let more highs come though. If the volume pot value is low it’ll choke off those highs. A higher value pot elsewhere won’t bring them back.
     
    Henry likes this.
  14. Henry

    Henry I Bleed Orange

    Apr 9, 2014
    Petaluma
    I haven't done it myself, but @jarrodtaylor makes sense. I've also seen it staggered like the Fender wide range humbuckers.
     
  15. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    The results will depend completely on the value of the cap. However, I don’t think that you are going to get what you want from either an in-line cap or a different pot value. Those will have an effect, but I suspect that the characteristics of the pickup are the real source of the problem. That. Broadtron is a lot closer to the characteristics of a Gibson Humbucker than it is to a Filtertron.

    Like any powerful humbucking pickup with wide bobbin spacing, the Broadtron is going to favor lower frequencies and not generate the same proportion of higher overtones as a Filtertron would. For many people, that sound is fine, and maybe even more desirable than the Filtertron sound. But a powerful humbucker with wide bobbin spacing in a hollow body is going to be darker sounding and can get pretty muddy with overdrive.

    My advice would be to look into replacing the neck pickup with something a bit more suited to your tastes.
     
  16. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    "My advice would be to look into replacing the neck pickup with something a bit more suited to your tastes."

    I did install a blacktop filtertron but it did not sound any different so I put the broadtron back.


     
  17. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    Do you play with all of the volume controls (on the guitar) turned up all the way?
     
  18. Rockhead

    Rockhead Electromatic

    49
    Mar 3, 2019
    Delaware county, PA
    Yes.
     
  19. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    It almost sounds like a treble bleed would help, but I wouldn’t stake my last nickel on it.

    FWIW, my G6122-1959 sounded wonky. I tried everything I could think of, and finally I did a treble bleed using the schematic below.

    This is sort of the opposite approach to the cap blocking lows coming off the pickup. The idea here is to pass highs around the volume control, but if you run your volume controls all the way up, it might not matter, all that much. It couldn’t hurt, however.


     
  20. ramjac

    ramjac Synchromatic

    790
    Aug 14, 2011
    Wisconsin
    I installed a bass cut on the neck pickup of my G5220. I used a .001 uF cap inline between the neck volume pot and the pickup selector switch. It drops the low end right out and makes for a biting overdrive sound.

    BUT, note that I’m using it with a T-Armond neck pickup, not the stock BT. It’s also an aggressive cut, not something I want in the circuit all the time. I made it switchable and use it mostly with both pickups on and out of phase to get a unique sound. .003uF or a bit higher might be closer to what you are looking for; .022 uF is probably too high and you may not hear a difference.

    Note also that the stock neck BT in my G5220 didn’t ever seem to get as muddy as you’re describing. Makes me wonder if there’s something else afoot in your harness/neck volume pot.
     
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