Passive Hi-pass filter for pickups

[Rock_on]

Ok, so I posted this on another forum but I don't have any answer yet so please help....

I finally found out the cause of my poor tone. I have a cheap china Strat btw.

    The bass side is so low it's almost flush to the pickguard. I don't have any money to buy a new pickup.

    What I did to find the problem is download guitar DIs and analyze it in my DAW. I saw that most have smooth roll off around 100-200hz area.

    Mine is rich in hertz on that area hahahaha. Ew! I tried putting a hi-pass filter with an eq around 150hz area with negative 12-18db roll off and suddenly the sound became clear! Crystal clear!

    So what capaictor value do I need and where? Before the Hot lug of the output jack? Or one caps after the hot of each pickup? The first one would be better if it's the the way to go since less components inside.

    I need a hi-pass capacitor that centers around 125-150hz with negative 12-18db roll off. What value do I need or how do I calculate it?

    Or if you have anything better I could do, please suggest.

After a while, I came across this website:

http://www.muzique.com/schem/filter.htm

Can I use this instead? Because it says the calculator assumes low impedance source. Pickups is a high impedance source isn't? Please correct me if I'm wrong.

I will be putting it before the hot of output jack. Will that affect how the circuit works? or the value from the results of the calculator? Because it also shows it needs a resistor after the caps...


I also need 12-18db Rolloff because that's where it sounds good... the calculator says it rolls of 6db only. Another question:

- Can i make it steeper? If not then,

- Does higher center frequency can simulate it?

[PBE6]

You may want to breadboard this as an external effect first, as you will lose some volume from your guitar.

Two cascaded passive HP filter stages (i.e. two in a row) would theoretically give you a 12 dB roll-off, although the real response will be less steep due to impedance issues. As a quick fix, try choosing a higher cutoff frequency. Extra stages may also work, but each additional stage will suck extra volume from your signal. Higher value resistors with lower value capacitors will combat this effect somewhat.

If the stages are identical, the nominal cutoff frequency is still 1/(2*pi*R*C).

[Rock_on]

Lol, what I discovered was funny hahaha

My pickups are so cheap that I need to.... wait...

So I tried to download an Eq Matching plugin for my DAW and I tried matching the DI track I downloaded with mine... it automatically tries to eq the target sound to look like the reference sound... you can emulate any pickups but not like the sustain or output... whatever...

The eq matching plugin made a roll off at 431hz! That high!

431hz Hi pass with 6db. That's how muddy my pickup is... it also changes how amps and pedals reacts to my guitar.


So for my final question... Can I use the calculator I posted? It gives me a capacitor value of 1.5nF. I would put it before the Hot lug of my output jack and after the volume to make it a global cut.

I tried putting 250,000 in the resistor input box.

[PBE6]

Yes, the calculator will work fine. I'd suggest using a higher resistor value if possible, a 1M resistor and a 470pF capacitor gives you a cutoff of about 340 Hz which is probably fine, and it won't lose too much volume. You could also try using a potentiometer/resistor combination (500k pot and 220k resistor would be fine) and a 1nF capacitor so you can sweep the cutoff from 210 Hz to 720 Hz and find which spot you like best.

[Rock_on]

What does that resistor do? Is the capacitor not enough to do the job? I've been wanting to ask this one a long time ago already :v

I tried 300-ish area... it does not satisfy me. I want 400hz area. But if that's the only way to go... why not? Rather than sticking with this muddy guitar. I'm so excited I'm about to hear the blanket mud to be removed from my guitar.

[Rock_on]

Oh I forgot, I don't want to use a pot. I want it fixed. Mud is removed around 400 and if above... I'll lose those important frequencies from my guitar.

[Ben Lyman]

What kind of pickups are they?
What kind of volume pots are in the guitar?
Would it be possible to replace the volume pot with a higher value to get a brighter tone from the pickups? Say maybe about 500k to 1M pot or something?

[Rock_on]

Nope. Stock pickups with 250k pots. Higher pot would just mask those garbage. If you'll look at the frequecy analyzer you'll see the frequency spectrum is almost flat. 100-200hz area is almost the same with mid frequency. Cutting that would focus on my mids.

I already tried it in my DAW. It sounds similar now to other guitars... lol it's funny that I did not know that is what a guitar is supposed to sound like... but hey I do not know anyone who has a good guitar here. I thought my guitar just have some balls... more than what humbuckers could give 😂😂😂😂

[PBE6]

If ~400 Hz is the right cutoff for you, go for it.

Taken together, the series capacitor and resistor to ground form a voltage divider. The output of this divider is taken at the junction, and the voltage here is given by:

V = R / (R + Zc)

where Zc is the frequency dependent impedance of the capacitor. We can modify this slightly to show the effect of the upstream impedance (e.g. from your pickup and controls) on the output voltage:

V = R / (R + Zc + Zpickup)

As Zpickup increases, V decreases and you get less volume at the output. Having a higher value resistor will minimize the effect of Zpickup on the output volume as the denominator becomes dominated by the R value.

For example, at 1kHz with Zpickup = 10k, R = 10k and C = 47nF, we have V = 0.43. If we change to R = 100k and C = 4.7nF, we have V = 0.70. Changing to R = 1M and C = 470pF, we have V = 0.74.

It is possible to change the low frequency content of a signal using just a capacitor and no external resistor, but what's really happening is that the upstream impedance Zin is interacting with the capacitor and whatever else downstream to form a frequency dependent voltage divider. In other words, there's ALWAYS a resistor there somewhere, it just might be hidden.

[Transmogrifox]

PBE6 has pointed out the difficulty doing this with a passive network.  Turn on a stompbox with a different input impedance than the rest, and it all changes.   If you design it for a nominal 1 Meg input impedance to something, then you can calculate the capacitors based on the resistance of your volume pot.  But it's still interactive with the tone control.

If you put the passive high pass AFTER the pot and tone, then if you roll off tone or volume, the network looks back into a higher impedance, and makes the cutoff go lower.

If you put the passive high pass filter right after the pickup, that is your best bet.  Cut-off will go higher if you plug it into a low impedance stompbox or amp.

I tried an LTSPICE simulation using a guitar pickup impedance model coming from some measured guitar PU impedance curves.

To get a -3 dB point on a 12 dB/octave HPF (-3 dB relative to the sim run without a filter), I get the following:
Guitar PU --> 8nF cap --> 470k resistor to ground --> 10 nF cap --> 250k Vol Pot --> 250k Tone series 22n cap --> 20 ft cable (220pF) --> 1Meg load.

It's not a straight-forward implementation.  Best thing with a passive is to use your ears.

Most reliable implementation is an active filter buffered on the input and output.  It can be a box on the floor which will be the first thing your guitar plugs into.

In this configuration you can approximate the -3dB cutoff by viewing it as though the 2 capacitors are in series and all resistors are in parallel:
Req = 1/[1/Rfilter + 1/Rtone + 1/Rvol + 1/Ramp]
Ceq = C1*C2/(C1+C2)

f3dB = 1/(2*pi*Req*Ceq)

This approximation calculates very closely to my simulation so I think it will be of some value if you need to use other capacitor values or a different resistor value.

[Rock_on]

I understand what PBE6 said amd how the formula works, the problem is I don't know what is the impedance and to be specific... impedance right before the hot of output lug.

Or just give me a closer hypothesis answer

-6db at near 400hz please. Both resistor and capacitor value

[Rock_on]

From volume min to max I would want a sweep from 300hz to 400hz. Tht would work for me.

[Rock_on]

I used the calculator again and put 1M in the resistor input and 390pF capacitor and it shows 400hz cut.

Can I use this? Will playing with my volume change the cut frequency?

[DavidRavenMoon]

You can't really pick the frequency the cap will work at unless you factor in the inductance of the pickups. And if you switch two pickups on together the frequency will change.

Different pickups is the better way to do it, but just try some caps in the .047 to .0047 range. The smaller the value, the higher the hi-pass roll off.

[Rock_on]

I followed the advice, I got 950k and 390pF capacitor.

So I only need to put the caps in series with hot right? Going to the hot lug of jack?

Then the resistor from the hot jack to ground of jack?

I understand I can't really pick the exact frequency, but the closer the better. Just say what I said is the right way I'll go do it right away... if not, then... lol i dunno xD

[PBE6]

Yes, give it a try. It's easily reversible if you don't like the sound.

[Gus]

Have you looked for the G&L Comanche or s500 wiring diagram?

[Rock_on]

Have you looked for the G&L Comanche or s500 wiring diagram?

Looks cool but I need a permanent cut cause you wouldn't want to hear those nasty garbage frequencies again

[Rock_on]

(Link at the end so PLEASE READ FIRST...) Okay, I've done it... SUCCESS!!! WOOOHOO!

But for every action there will always be a reaction and that reaction is:

- I've got a massive (I dunno... you tell me) volume drop. Usually my gain on my interface is just about 9 'o clock to 10.30 but now it's on 12.30 to 1 'o clock. If I did this in a real amp I can determine if it's a big drop. I don't even know how much gain my interface add from 9 'o clock to 1 'clock.

- Okay now that I have set the right amount of gain, I can clearly hear the difference in my DAW. My guitar suddenly sounds like an HD guitar HAHAHAHA but I dunno if it's too much but I'm pretty happy with it. I listened again to my reference DI and eq match it... the bass now is similar and not SAME. I have a bit or medium amount of high and no wonder cause I still have my bass side almost flush to the pickguard and this is a STRAT duh :v I'll just try to balance it again OR find a bit bigger value capacitor. I used 390pF.

- I can now sound like my reference pickup sound but I need to rollback the tone knob to about 4 - 5 (Log pot) and again, it causes the volume to drop off a bit... the sound wave in my DAW may not be that accurate (I dunno again :v lol)


So another question again, what will be the side effects if I will be using greater than 1M value? Will that bring my gain back to considerable amount also? I want to bring back my gain a bit higher... well if I'll just be using my interface and an amp sim... no problemos but for other situation :v :v :v


Listen to this:

1st is the original sound
2nd is the new sound
3rd is the new sound with the tone knob at 4-5
4th .... YEA! \m/ my reference cool pickup sound! It just have a bit more mids or balls considering it's a humbucker (I guess cause it's metallic. EMG maybe? Lol I don't know anything about pickup, I just see them on the internet)

https://www.dropbox.com/s/prje1uneqb6b8cc/Pickups%20Comparison.wav?dl=0

[Rock_on]

If ~400 Hz is the right cutoff for you, go for it.

Taken together, the series capacitor and resistor to ground form a voltage divider. The output of this divider is taken at the junction, and the voltage here is given by:

V = R / (R + Zc)

where Zc is the frequency dependent impedance of the capacitor. We can modify this slightly to show the effect of the upstream impedance (e.g. from your pickup and controls) on the output voltage:

V = R / (R + Zc + Zpickup)

As Zpickup increases, V decreases and you get less volume at the output. Having a higher value resistor will minimize the effect of Zpickup on the output volume as the denominator becomes dominated by the R value.

For example, at 1kHz with Zpickup = 10k, R = 10k and C = 47nF, we have V = 0.43. If we change to R = 100k and C = 4.7nF, we have V = 0.70. Changing to R = 1M and C = 470pF, we have V = 0.74.

It is possible to change the low frequency content of a signal using just a capacitor and no external resistor, but what's really happening is that the upstream impedance Zin is interacting with the capacitor and whatever else downstream to form a frequency dependent voltage divider. In other words, there's ALWAYS a resistor there somewhere, it just might be hidden.

I got how it works and what you mean but I can't compute it myself. What unit should I use for Zc? Farads? uF? nF? pF?


I'm thinking about using 10M as a resistor and a capacitor that would cut at 400hz area. Is there any bad side effects of exaggerating resistor value? Aside from the capacitor may not be available? Of course I would get the nearest value.