Hi-pass/low-cut passive filter on a guitar?!

Discussion in 'Pickups, Electronics & General Tech' started by Ostia Man, Jun 21, 2008.

  1. Ostia Man

    Ostia Man SS Contributor

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    is this posible?
    I was messing around in the studio, and i cut everything under 80-100Hz before any distortion(amp), beacuse i figured:idea: I dont need it in the mix so Ill get rid of it from the start. I must say it really makes the guitar sound very well defined and it get rid of all the muddyness:hbang:. I had to cut again after the amp because the amp, for some reason, was heavy below 100Hz.
    So, if I dont need it in the mix, I dont need it live.
    Can I mod my guitars to have a passive low-cut/hi-pass filter?
    I have search in google but cant find anything
     
  2. Emiliano

    Emiliano true DJENTleman

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    you can do it, but expecially for live uses
    i'll stick with a rack parametric equalizer.

    just because as you saw in the studio an amplifier would
    still add something in that audio band, so i'll cut that after with an EQ

    m2c
     
  3. eleven59

    eleven59 None shall pass.

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    Definitely, in any mix, I always roll off everything on the guitars that would interfere with bass and kick (usually 130hz-ish and below).

    You could add an EQ live to roll that off if you want to tighten things up (it's what I use the graphic EQ on my bass amp for, as I play bass in my band), but if you're in a decent venue with a decent PA and decent sound guy, they'll be doing that for you.
     
  4. dpm

    dpm Oni Guitars

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    A capacitor in series with the signal will act as a high pass filter. I'm not sure what value you'll need, it will take a little experimentation but caps are cheap. Maybe start at .1uF?? LoC and JBroll need to chime in here, I always forget this stuff :lol:
     
  5. Demeyes

    Demeyes SS.org Regular

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    Would I be wrong in thinking that most cabinets/amps aren't going to amplify these signals anyway? They get cut off along the way.
     
  6. Scali

    Scali Banned

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    Yes, most guitar speakers will drop off at about 120 Hz, and by 80 Hz they'll be really weak.
    So they filter out most of the 'rumble' in the guitar sound.

    Filtering out bass before the distortion is a good idea. My amp actually has input filters built-in, you can engage a low-pass or a high-pass filter (or both) on the input.
    This is also what overdrive pedals are often used for. Eg the TubeScreamer is quite popular because at low gain settings and the tone wide open, it will basically be a high-pass filter aswell (often with a bit of gain boost). And Brian May uses a special treble booster device, which essentially has the same effect.
    I always use a treble booster on my lead channel (I don't use the built-in filters, because they affect all channels and can only be enabled/disabled from the front panel, not with a footswitch). I have also selected my preamp tubes to have relatively high treble response. I've used EHX for a while, and I currently use Chinese 12AX7 tubes, because they have a really tight bottom end and lots of singing/screaming harmonics, mostly because they have high gain, but mostly in the mid-high to high frequencies, and only medium bass response. Tubes with more bass response, such as JJ ECC83S don't nearly sound as tight and 'exciting' when overdriven in my amp.
     
  7. SplinteredSoul

    SplinteredSoul 7 String FTW

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    There's pleanty of effects out there that can do this. I have it in my G-System, but as for in the guitar? I'd guess you'd be looking to modify bass controls, as they're more likely to exist.

    Agreed.


    (Celestion G12)
    [​IMG]
     
  8. Ostia Man

    Ostia Man SS Contributor

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    Cool, so it is pocible.

    thats why I whant to cut them before the amp.
     
  9. noodles

    noodles <font color=#FF0000><b>I'm your huckleberry</font>

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    Honestly, doing this kind of thing live is an excellent way to neuter your guitar tone. Do you really want to clutter up your signal chain with this kind of stuff? It's better left to the soundboard, since you ALWAYS want to work with the miced signal. :2c:
     
  10. Scali

    Scali Banned

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    You can't cure muddy, fuzzy distortion at the soundboard.
    You need to eq it before the distortion. Filter out the problem frequencies before they clutter up the distorted signal.
     
  11. eleven59

    eleven59 None shall pass.

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    So, get a better amp or set the controls better :2c:
     
  12. Rick

    Rick ALL HAIL DJOD

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    Hey Noodles, I like your new rep. :lol:
     
  13. Ostia Man

    Ostia Man SS Contributor

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    exactly. similar to a clean boost with an od, without the boost, just tight.
     
  14. JBroll

    JBroll Hard-On For Freedomâ„¢

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    Okay, cutting bass before the amp and cutting bass after the amp are going to be completely different.

    If you have a stock Tube Screamer (i.e. not one that has had its bass response improved), it's going to roll everything but mids down automatically. Because of this, I'd just use a TS or similar pedal (you can build one into your guitar if you want, they can be very simple) - this is also why the big producers and a lot of bands you'll see use a TS in front of their amp... a lot of amps just don't handle bassy inputs well, and midrange is what hits these amps better. Passive filters in a guitar, though... wouldn't recommend.

    If you read High-pass filter - Wikipedia, the free encyclopedia, you can figure out a resistor-capacitor pair that'll do the job, but I would strongly consider just building a tiny TS-clone and shoving that in the guitar. Yeah, you'll have to change your batteries once in about every three blue moons, but oh well.

    Again, don't forget that cutting 80Hz before an amp MIGHT NOT (Fixed: I'm a twit. - JBroll) mean reduced content around 80Hz after the amp. I'd just leave the job of EQing the output to the board, this sort of thing will only tighten the tone up and get rid of some of the 'flub' in the input signal.

    Jeff
     
  15. Ostia Man

    Ostia Man SS Contributor

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    I know nothing about electronics, I read the wikipedia, but the only thing i could get was the cap in series and the resistor parallel, but how do I find the values I need to cut 80-100Hz?
    I dont want to cut the rumble after the amp, I can cut that in the mix. I just want to make the guitar a little bit tighter in clean and in lower to medium gain settings, hi gain is almost alway with a ts, mxr ZW or some kind of boost.
     
  16. Ostia Man

    Ostia Man SS Contributor

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    I promise to make before and after clips:hbang:
    please?
     
  17. Scali

    Scali Banned

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    It doesn't work that way, sadly.
    There is only one line of amps that I know of that allows you to eq before and after distortion, and that is the Mesa Mark series.
    Nearly all other amps have only one eq, which is either placed before (Fender style) or after (Marshall style) the gain stages that provide (most of) the distortion.

    So in other words, aside from the Mesa Mark series, there is no way to "set the controls better", because the controls you need simply aren't on the amp. So you add a pedal or rack effect to fix that.
    I have a Marshall 6101, which has the eq after the distortion, so I use a treble boost before the distortion. Problem solved.

    The worst of it all is that different channels require different amounts of pre/post eq.
    Some multi-channel amps have only one set of controls, so you can make at most one channel sound perfect at a time, and have to readjust everytime you switch.

    Then there are multi-channel amps that do have individual eqs for every channel, but often they still share part of the preamp, which means that whatever filter the amp has on the input, is only 'tuned' for one channel at most.
    This is the reason why so many 2/3-channel amps have great hi-gain sounds, but really poor cleans and crunch sounds.

    Only the most expensive amps actually have almost completely separate preamps for each channel, and don't sacrifice one sound for the other (I am one of the lucky few to have an amp with classic Bassman/JTM45 cleans, Plexi/JCM800 crunch and Bogner-like hi-gain, all rolled into one). But even then, an all-tube sound is different from a tube distortion boosted by a solid-state pedal... so still some people prefer to boost their signal. The solid-state boost will give you a tighter attack.

    Not necessarily true.
    If you use a lot of gain, the tone will be highly saturated/compressed, so the actual level of signal output won't change if you cut a bit of input.
    The primary effect is that it will saturate differently, giving a more 'transparent' tone, where you can hear more sonic detail... but that doesn't mean the frequency response is drastically different. In fact, the bass output might become more powerful/dynamic because it is compressed less (which is why it sounds tighter).
     
  18. dpm

    dpm Oni Guitars

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    ^what Scali says is exactly right.

    EQ'ing pre-distortion is vastly different to EQ'ing post distortion.

    JBroll, question for you....

    I just tried numerous caps in line with the signal, without the resistor, and successfully removed bass from the guitar signal. Does the coil and volume pot resistance take the place of the resistor? I was surprised at the cap value range, .001uF is a good starting point IMO. I didn't do anything scientific, just a quick cycle through various values comparing them to the un-filtered signal. As expected the level hitting the amp is lowered, but I didn't find it bothered me too much. Certainly something I'm interested in experimenting with more as I'm not really a TS kind guy, I just can't get into them, but I do like to tighten things up pre-gain.
     
    Last edited: Jun 24, 2008
  19. JBroll

    JBroll Hard-On For Freedomâ„¢

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    Oh, balls, I got that backwards. Yeah, reducing 80Hz beforehand doesn't necessarily mean reducing 80Hz on output, I was trying to avoid a double negative and wound up without a negative at all. Fuck me running, that was silly.

    Anyway, dpm, the volume pot does act as a resistor. The cutoff frequency there, assuming a 500K pot, would be

    1/(2*pi*R*C)

    = 1/(2*pi*[5*10^5]*[1*10^-9])

    ~~ 318Hz

    so that's not unusual... although EQ circuits are occasionally counterintuitive, it's pretty clear that you've low-passed your signal well enough.

    Of course, you lose gain with these, but seeing as how we have gain knobs in this day and age that's not too relevant.

    Jeff
     
  20. dpm

    dpm Oni Guitars

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    So, a .0033uF cap should give a cutoff frequency of 96Hz with a 500k pot, if I've done my calculations correctly :scratch: Seems the safest bet would be to try caps from .0047 - .001 (marked 472, 332, 222, 102) and see what works best, keeping in mind that such a simple filter likely has a more gentle slope than other methods.
     

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