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



## Ostia Man (Jun 21, 2008)

is this posible? 
I was messing around in the studio, and i cut everything under 80-100Hz before any distortion(amp), beacuse i figured 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. 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


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## Emiliano (Jun 22, 2008)

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


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## eleven59 (Jun 22, 2008)

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.


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## dpm (Jun 22, 2008)

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


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## Demeyes (Jun 23, 2008)

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.


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## Scali (Jun 23, 2008)

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.


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## SplinteredSoul (Jun 23, 2008)

Ostia Man said:


> is this posible?
> I was messing around in the studio, and i cut everything under 80-100Hz before any distortion(amp), beacuse i figured 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. 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



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.



Demeyes said:


> 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.



Agreed.


(Celestion G12)


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## Ostia Man (Jun 23, 2008)

dpm said:


> 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


Cool, so it is pocible.



Demeyes said:


> 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.


 thats why I whant to cut them before the amp.


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## noodles (Jun 23, 2008)

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.


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## Scali (Jun 23, 2008)

noodles said:


> 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.


 
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.


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## eleven59 (Jun 23, 2008)

Scali said:


> 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.



So, get a better amp or set the controls better


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## Rick (Jun 23, 2008)

Hey Noodles, I like your new rep.


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## Ostia Man (Jun 23, 2008)

Scali said:


> 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.


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


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## JBroll (Jun 23, 2008)

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


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## Ostia Man (Jun 24, 2008)

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.


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## Ostia Man (Jun 24, 2008)

I promise to make before and after clips
please?


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## Scali (Jun 24, 2008)

eleven59 said:


> So, get a better amp or set the controls better


 
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.



JBroll said:


> Again, don't forget that cutting 80Hz before an amp will mean reduced content around 80Hz after the amp.


 
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).


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## dpm (Jun 24, 2008)

^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.


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## JBroll (Jun 24, 2008)

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


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## dpm (Jun 25, 2008)

So, a .0033uF cap should give a cutoff frequency of 96Hz with a 500k pot, if I've done my calculations correctly  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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## JBroll (Jun 25, 2008)

The dropoff rate is on the Wikipedia page or somewhere near it, of course that's important but I didn't feel like doing it. This has not been a happy couple of weeks and I've been slacking big time on this stuff, but if you're still interested in this tinkering in about two or three weeks I'll be in better shape.

Jeff


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## Ostia Man (Jun 26, 2008)

dpm said:


> So, a .0033uF cap should give a cutoff frequency of 96Hz with a 500k pot, if I've done my calculations correctly  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.


so you say that a .0033uF cap will have a cut of on 96Hz with a 500k pot.

how do you wire it in the guitar?
also I use 1000k pots, so what will be the value of the cap I need?
and how much is the output reduced?


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## dpm (Jun 26, 2008)

JBroll said:


> The dropoff rate is on the Wikipedia page or somewhere near it, of course that's important but I didn't feel like doing it. This has not been a happy couple of weeks and I've been slacking big time on this stuff, but if you're still interested in this tinkering in about two or three weeks I'll be in better shape.
> 
> Jeff


 
Totally understood, I'm in a similar boat here with a hell of a lot going on (and wrong) which is why my own replies have been less than ideal. I figure it'll take longer to calculate various dropoff rates than it does to simply try out a few caps. Considering we don't know exactly how Ostia Man is cutting the lows in the studio I thought it safe to mention slope. Take care man, I hope everything is back to good soon.




Ostia Man said:


> so you say that a .0033uF cap will have a cut of on 96Hz with a 500k pot.
> 
> how do you wire it in the guitar?
> also I use 1000k pots, so what will be the value of the cap I need?
> and how much is the output reduced?


 
You need to wire it between the output jack and the component before that, which will be either the volume pot or switch depending on the guitar in question. In most guitars with a master volume the best thing to do is to disconnect the output of the pot (middle lug) and connect the cap between that point and the wire you just disconnected.

For 1000k these should be the frequencies, the cap marking is in brackets

0.001uF (102) = 159Hz
0.0015uF (152) = 106Hz
0.0022uF (222) = 72Hz


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## dpm (Jun 26, 2008)

One other thing.... get some alligator leads so you can test the different cap values without having to solder them in.

Arbor Scientific Online! - Alligator Leads (Pack of 10)


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## Ostia Man (Jun 27, 2008)

thanx!!
by the way what I did was just record the guitar direct, and in the process of reamping I cut some lows with a waves eq plug-in. just goofing around.


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## JBroll (Jun 27, 2008)

Ostia Man said:


> so you say that a .0033uF cap will have a cut of on 96Hz with a 500k pot.
> 
> how do you wire it in the guitar?
> also I use 1000k pots, so what will be the value of the cap I need?
> and how much is the output reduced?



I'd aim for a higher cutoff, like 300-400, and work down from there if it seems too thin. The amp will add plenty of bass later, you'll be fine. Hell, the guys on the records you hear are using Tube Screamers before their amps, and basically if something's not 700-800Hz it's losing gain.

Just look at the Wikipedia diagram, and cut the value of the caps in half. As for output... can't say, as there's the technical dropoff and then the apparent dropoff.



dpm said:


> Totally understood, I'm in a similar boat here with a hell of a lot going on (and wrong) which is why my own replies have been less than ideal. I figure it'll take longer to calculate various dropoff rates than it does to simply try out a few caps. Considering we don't know exactly how Ostia Man is cutting the lows in the studio I thought it safe to mention slope. Take care man, I hope everything is back to good soon.
> 
> 
> 
> ...



No, you can just take a calculator or spreadsheet and put the function in one cell, and then have two columns - one with cap values, the other with the function of the cap values - to compare caps and dropoff rates.

Jeff


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## luca9583 (Jun 18, 2013)

Still related to this topic..would it be possible to do the following in order to achieve a specific 1-2k boost for a _single string_ only:

- install a single string pickup under the lowest string between the bridge and the bridge pickup

- install two caps to filter out everything below 1k and everything above 2k

- install a blend pot to "mix in" the 1-2k boost with the bridge pickup's main signal


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## InfinityCollision (Jun 18, 2013)

Possible, yes. What you want is called a band-pass filter. The exact design would depend on the results you're seeking. Out of curiosity, how would you intend to use such a design? That's quite a bit of range you're attenuating, even with the electric guitar's typically limited signal (which usually drops off significantly below 80-120 Hz and above 4-5kHz).


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## luca9583 (Jun 18, 2013)

InfinityCollision said:


> Possible, yes. What you want is called a band-pass filter. The exact design would depend on the results you're seeking. Out of curiosity, how would you intend to use such a design? That's quite a bit of range you're attenuating, even with the electric guitar's typically limited signal (which usually drops off significantly below 80-120 Hz and above 4-5kHz).




It's a guitar with a 34" scale..tuned to low B0. I want to be able to apply that 1-2k boost on the lowest string only..to get more bite out it to match the other strings. So the guitar's normal pickup would be on as normal, while the heavily filtered single string pickup would be blended with the normal pickup


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## InfinityCollision (Jun 18, 2013)

Hmm.. The thing about simple band-pass designs is that it's not really a boost as such (can't be with a passive design). They will attenuate signals outside the passband, with signals further from the passband experiencing progressively greater attenuation. Thus the impression of a boost at the frequencies within the passband. If that's fine (which it may be with the blend, especially if you're using lots of gain downstream; the fundamental and lower overtones would come across slightly "cleaner" than the upper harmonics) then you could go band-pass, otherwise you may want to stick an EQ in instead, prior to blending the signal with the other strings. If you want a comparison prior to doing any wiring, run that string through a Tubescreamer with the gain all the way off and the tone knob dimed. The result is fairly close to what you'd get with a filter, though with any potential volume boost from the pedal present and a slightly wider "hump" that's centered a bit higher, but still covers your specified range pretty well. Shouldn't be all that different with such a low fundamental.

If you do try that Tubescreamer test, see if you prefer the sound with the tone knob dimed or if you're getting the results you're after with it rolled off a bit (which moves the hump progressively lower, to around 500Hz when set to minimum). You don't break 1kHz on the open B0 until the 33rd harmonic... even the octave B1 won't break 1kHz until the 17th harmonic. Not a lot of signal content that high up the harmonic sequence, particularly for thick strings, so you may find a boost centered slightly lower (700-1.5kHz range perhaps?) is what you want.


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## luca9583 (Jun 19, 2013)

Cool. Yes that's what i was thinking. To fine tune the frequencies
to boost for this string, i think an onboard active eq
is the way to go. The Ibanez LF7 seems like it could
be perfect..it has two adjustable cut off controls, drive and level.

The level control would be useful because it could compensate for
having to reduce the volume of the main pickup too much
when blending


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## saxman42 (Jun 22, 2013)

dpm said:


> 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



You can use this circuit:

File:High pass filter.svg - Wikipedia, the free encyclopedia

and this calculation:

f=(2*pi)/(RC)

Let's supposed you're using 500k pot/ resistor:

100 Hz = (2*3.1415)/(500k * C)

solving for C: C= 125.66 nF (0.12566 uF)... Damn good guess dpm!
This can be done with a switch or normal tone control. The switch would be more precise, but a tone control would give you the ability for tweaking.


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