Bass cut = high pass filter question

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars
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nunonaos
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Post by nunonaos »

Hello
I want to include a high pass filter in my les paul, i think it will be a usable tone, kind of giving it more of a strat tone.

All the schematics i've seen from high pass filters include a resistor to ground after the capacitor, like this:
https://www.google.com/url?sa=i&url=htt ... AdAAAAABAD

On the other hand, on the wiring schematics (from guitar related sites) like the reverend schematic they only use a resistor to blend the capacitor in the circuit, they don't include a resistor to ground after the capacitor.
https://www.google.com/url?sa=i&url=htt ... AdAAAAABAD

So what's the deal with this?
Can I assume that the resistor is the input inpedance on the amplifier (or effect pedal, etc) after the guitar? Or the resistor is the existing resistance in the pickups and guitar pots?

I'm confused.

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andy-h-h
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Post by andy-h-h »

If you run signal through a relatively small cap, you loose bottom end. That's a 2n2 cap which is pretty small. The pot is introducing that cap to the signal path, cutting bass as this happens (the guitar wiring schematics, not the high pass filter schem)

Maybe a a varitone type switch could be cool, have a few different size caps running from full range to a lot of cut. I like switches as you always get the same result, rather than trying to dial in a pot.

nunonaos
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Post by nunonaos »

andy-h-h wrote:
21 May 2020, 22:36
If you run signal through a relatively small cap, you loose bottom end. That's a 2n2 cap which is pretty small. The pot is introducing that cap to the signal path, cutting bass as this happens (the guitar wiring schematics, not the high pass filter schem)

Maybe a a varitone type switch could be cool, have a few different size caps running from full range to a lot of cut. I like switches as you always get the same result, rather than trying to dial in a pot.
What I don't understand is why is it that all the high pass filter schematics have a resistor to ground (that changes the frequency cutoff) and the guitar schematics don't..

I just tried with a 1mohm resistor to ground and it does affect the sound.
Also I just noticed that when I roll the pot and blend the cap I ear more hum...with the resistor and without.

I would like to check a reverend guitar to see how they do it, but at least with this guitar I don't like the result that much.
With my Les Paul using a 1n cap I ear some bass cut but also some mids cut, in fact I think I ear more volume loss then bass cut. It's more like lowering the volume a bit then changing the sound like when you use a standard tone (cut) pot.

nunonaos
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Post by nunonaos »

I think I finally understand

The high pass filter needs a resistor to ground after the cap, FACT!

On the reverend guitar they use the bass cut BEFORE a master volume, that master volume functions as a resistor to ground...

In my case, I'm using dual volumes (one for each pickup) before the bass cut, so I need a resistor to ground because I don't have any volumes after the bass cut.

Optical
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Post by Optical »

Your amp or pedals also have a resistor to ground on the input, usually 1M. So a series output cap forms a highpass filter when combined with the amp input resistor.
Read up on "RC filters"
Can calculate the cutoff frequency using the formula 1/2.pi.R.C, or just use an online calculator and input your R and C values
http://sim.okawa-denshi.jp/en/CRtool.php

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Cub
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Post by Cub »

It'll take a bit more work, but I'd like to suggest an LCR filter, such as Bill Lawrence Q-Tone. It will give you a much better guitar sound than a RC HPF.
As some say, it's as if it takes windings off the pickup. The guitar still sounds like a proper guitar, but with lighter wound pickups. How much lighter? That will depend on where you put the knob.

You don't have to sacrifice one of the four stock knobs for this. Just put it on the switch of a push pull pot with an internal trimpot and you're good to go.
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nunonaos
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Post by nunonaos »

My pickups are fairly low output, they're just a bit muddy on some amps.

But that idea of a high pass with an inductor sounds good... I'll see if I can get a inductor

nunonaos
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Post by nunonaos »

Optical wrote:
22 May 2020, 06:39
Your amp or pedals also have a resistor to ground on the input, usually 1M. So a series output cap forms a highpass filter when combined with the amp input resistor.
Read up on "RC filters"
Can calculate the cutoff frequency using the formula 1/2.pi.R.C, or just use an online calculator and input your R and C values
http://sim.okawa-denshi.jp/en/CRtool.php
Thanks for the reply, I've read a bit about the rc filters and that was the reason I didn't understand why reverend didn't needed a resistor to ground, just later I realized that it was the volume pot that was the resistor to ground

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Cub
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Post by Cub »

nunonaos wrote:
22 May 2020, 10:32
My pickups are fairly low output, they're just a bit muddy on some amps.
But that idea of a high pass with an inductor sounds good... I'll see if I can get a inductor
It's not a matter of output, but of resonance. But I suppose you'll perceive a loss of some output that way as well, as with any passive filter.

Below is a link to something very similar to what I had in my own Les Paul at one time. The biggest difference is that I had it on a push/pull pot for both pickups at once.
https://www.premierguitar.com/articles/ ... d-expanded

I found that the best way is to start by toying around with values for the cap and resistor for the neck pickup. Then, put the pickup selector switch in the middle position and find the right ones for the bridge pickup by trial and error until you hear something that's somewhere between a Strat quack and a Tele cluck.
The values mentioned in the article are a great starting point.

Keep in mind, though, that I rewired to to master tone and Q-Tone after I got Bill Lawrence's Q-Tone Filter and never looked back.
I wish I were a chestnut tree, nourished by the sun.
With twigs and leaves and branches and conkers by the ton.

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