high pass/ low pass filter

[jaibot]

hello
today I was in physics class and we learned about high and low pass filters. I was wondering if the tone control in a typical bass guitar is actually a low pass filter? If this is so, then has anyone tried a high pass filter just for fun? On the same topic are the bass/mid/treb controls on my amp just high and low pass filters?
Just looking to figure the practical applications of high and low pass filters in items i commonly use.

[bongomania]

Yes, a passive tone pot is a low-pass filter. All EQ, whether active or passive, is a filter. Bear in mind though, that there are several types of filter other than just high pass and low pass.

[jaibot]

alright! i guess i need to learn a bit more to get to the other filter types.
Have you ever heard of anyone using a high pass filter as a tone control in a bass? I might try it as a small project.

[Jazz Ad]

G&L basses have high and low pass filters in their preamp.
The high pass is widely used on live mixers to keep the lower end clean.

[line6man]

Rickenbacker basses sometimes have high pass switches.

The switch places a capacitor in series with the signal path to block lows and pass highs.

[darkstorm]

Originally Posted by jaibot

alright! i guess i need to learn a bit more to get to the other filter types.
Have you ever heard of anyone using a high pass filter as a tone control in a bass? I might try it as a small project.

I used a simple high pass filter for the neck pup of a gibson ebo3 bass long ago. So the neck pup would sound better instead of just being toneless bass thump. Though an acitve bass control with cut and boost along with a active treble with cut and boost would be much more versatile for getting your high pass sound better. Perhaps by just cutting bass some or boosting treble or a combo of these two. These can create diff sound trebly wise more efficiently and with more variety then just simple passive capacitor type filters.

You could also use a 3-5 position switch to select diff caps for high pass filter tones selection for passive version though.

[Stealth]

Originally Posted by jaibot

hello
today I was in physics class and we learned about high and low pass filters. I was wondering if the tone control in a typical bass guitar is actually a low pass filter? If this is so, then has anyone tried a high pass filter just for fun? On the same topic are the bass/mid/treb controls on my amp just high and low pass filters?
Just looking to figure the practical applications of high and low pass filters in items i commonly use.

Pandora's box there, my friend.

As bongomania explained - the tone control on a bass is a lowpass filter, where the potentiometer's sweep changes the cutoff frequency. As Jazz Ad, line6man said and darkstorm, G&Ls and Ricks (and the occasional home-modded bass ) have highpass filters, where you either have a potentiometer that changes the cutoff frequency or a fixed capacitor that sets a specific cutoff frequency.

Since most of those tone controls are made from one resistor and one capacitor, they're considered first-order pickups. More complex filters (such as second-order ones) can be made to either cut off a specific band of frequencies (band-reject filters, or notch filters if the band is extremely narrow) or pass only that band of frequencies (band-pass filters). And that's as far as you can get with passive electronics.

Okay, a bit of imagery here:

Low-pass filter, starts cutting at 1 kHz - notice that at 1 kHz you've already lost 3 dB of volume (about half of it), and the higher the input frequency the quieter the output will be.

High-pass filter, starts cutting at 1 kHz - the exact reverse of the low-pass.

Band-pass filter, wide, centered on 1 kHz, passing from about 700 Hz to 1400 Hz.

Band-reject filter, very narrow (notching), centered on 1 kHz. The notch itself actually goes to negative infinity, completely cutting off that frequency.


With active electronics (preamps, equalizers) a few more filters spring to mind:

• the shelving filter - boosts or cuts all frequencies above/below a certain frequency, the amplitude response (behavior) looks like a shelf; e.g. starts boosting at 2 kHz, hits the maximum at 4 kHz and keeps level from that frequency onward
• peaking filter - boosts a frequency and some of its surroudings, the amplitude response looks like a hump or a dip, e.g. centered on 1 kHz, gradually boosting from 500 Hz to its maximum at 1 kHz, then sloping down to unity gain (or no boost at all) at 2 kHz
• allpass filter - the amplitude of all frequencies remains the same as before the filter - however the phase (indirectly - the shape of the signal) changes. If you add an allpass-filtered signal to its original, it'll get a notch at that frequency - useful if you're making a phaser, for instance.

More imagery:

Low-pass shelf, boosting by 6 dB

High-pass shelf, cutting by 6 dB

Mid-peak, wide, boosting

Mid-peak, narrow, cutting


Any - and I mean any - of those can be used in a bass. Passively speaking, LP filters are the most common tone control, with the occasional HP or notch filter built in (usually as part of a Varitone control). Actively speaking, most preamps are either two-band with a low-shelf and a high-shelf, or a threeband with a low-shelf, high-shelf and mid-peak, sometimes with a variable center frequency for the mid.

Equalizers are usually a batch of mid-peak filters with the low and high shelves for the outermost fequencies (say, 30 Hz and 16 kHz). Phasers are made with multiple narrow-band notches that move around. Flangers have multiple narrow-band notches as well, but uniformly spread.

[greenboy]

And of course, in a passive bass the circuit includes the cable going to the preamp/head, and the preamp/head's input impedance affects their actual disposition too.

[SGD Lutherie]

Originally Posted by Jazz Ad

G&L basses have high and low pass filters in their preamp.

G&L actually uses passive tone controls. They aren't associated with the preamp at all and work in passive mode.

I had the same controls in my Rick back in '78. I got the schematic from an old Carvin pickup I bought.

Now the real fun starts with active filter that you can sweep.

Here's an example of a low pass and high pass filter:

LP/HP

[jaibot]

whoah thanks a lot guys, these circuits are cute as hell. We went over a band pass filtar today in class, which is just a capacitor and resistor in series, right? Could i use one tuned to 60 H to effectively take out 60 cycle hum? I want to learn as much of this stuff as i can so by the end of high school ill be able to build some cool stuff of my own. Any opinions on books to learn from? I already started going through newnes know it all circuit design.

[greenboy]

You really can't tune the circuit effectively without knowing the stuff mentioned in post #8 I don't think. And you'll never get the slope you need to be effective, nor be able to deal with the 60-cycle harmonics. Passive bass circuits are pretty hit-or-miss.

There is always good shielding, and humbucker techniques, however ; }

[jaibot]

ah that makes a lot of sense. Plus with the =- 20% of capacitors it would be hard to get the precise 60hz out of the signal. I actually have my bass shielded (did it myself and i think i did a decent job) but it still buzzes a ton when front or back of the bass is facing the amp. When the side of the bass is facing the amp the hum goes away.

[bongomania]

Originally Posted by jaibot

Any opinions on books to learn from?

Buchla & Floyd's "The Science of Electronics" is a good intro textbook, relatively easy to read. Also check out all the "Rane Notes", that is, tech notes published by audio company Rane. They are among the best resources anywhere, and all their papers are free online. Here's one that should be committed to memory: http://www.rane.com/note110.html

[line6man]

Originally Posted by jaibot

whoah thanks a lot guys, these circuits are cute as hell. We went over a band pass filtar today in class, which is just a capacitor and resistor in series, right? Could i use one tuned to 60 H to effectively take out 60 cycle hum? I want to learn as much of this stuff as i can so by the end of high school ill be able to build some cool stuff of my own. Any opinions on books to learn from? I already started going through newnes know it all circuit design.

"Cute as hell?"

There are two problems with removing 60Hz.

First off, 60Hz is only the fundamental. There are also upper harmonics that contribute to the hum you hear.

Second, decreasing the amplitude of the 60Hz frequency band also affects your signal, not just the hum.
You will lose a lot of bass.

[synaesthesia]

You want to read this:

http://www.amazon.com/Active-Filter-...2535997&sr=1-1

[SGD Lutherie]

Originally Posted by line6man

"Cute as hell?"

Reminds me of something my wife would say... I was wiring up a circuit board the other night and she came over, looked like a dear in the headlights, and said "you enjoy doing that stuff, don't you?" I think the very thought gave her a headache!

There are two problems with removing 60Hz.

First off, 60Hz is only the fundamental. There are also upper harmonics that contribute to the hum you hear.

Second, decreasing the amplitude of the 60Hz frequency band also affects your signal, not just the hum.
You will lose a lot of bass.

Yeah, you mostly hear the rectified 120Hz buzz. Filters wont help with single coil hum without also removing notes in that range.

[line6man]

Originally Posted by SGD Lutherie

Reminds me of something my wife would say... I was wiring up a circuit board the other night and she came over, looked like a dear in the headlights, and said "you enjoy doing that stuff, don't you?" I think the very thought gave her a headache!



Yeah, you mostly hear the rectified 120Hz buzz. Filters wont help with single coil hum without also removing notes in that range.

Actually, it reminds me of something my 5th grade teacher would say. She thought it was so cute that I was obsessed with electronics when I was 12. I actually wrote a short story about how funny I thought it was that I accidentally wired a component backwards and it exploded.

[xaxxat]

Tone stacks can be interesting, and cute too. You can find a tone stack calculator here:

http://duncanamps.com/tsc/index.html

It's geared for amps but is a good way to observe the response curves.

[lowfreqgeek]

Originally Posted by jaibot

Any opinions on books to learn from?

The Mother of all Electronics books: The Art of Electronics by Horowitz and Hill. I keep about 3 copies around (between work and home) and refer to it all the time. It was a text book in college, but 10 years later it's my go-to source. It starts with the fundamentals and builds from there.

[lowfreqgeek]

Originally Posted by bongomania

Buchla & Floyd's "The Science of Electronics" is a good intro textbook, relatively easy to read. Also check out all the "Rane Notes", that is, tech notes published by audio company Rane. They are among the best resources anywhere, and all their papers are free online. Here's one that should be committed to memory: http://www.rane.com/note110.html

Speaking of Rane, this is the best data sheet in the history of data sheets, IMO, of course.

Rane PI-14