LPF vs. Shelving -dB treble EQ

[Nyarlathotep]

Found some schems online for an LPF, and am about to look for some shelving type -dB treble EQ ones:

http://www.discovercircuits.com/PDF-...wPassFilt1.pdf

Anyone know how to change the values/add pots to change the cutoff freq?

Oh, and is there any diff between an LPF and shelving treble EQ?

This page has some treble/bass shelving schems: http://www.headwize.com/projects/sho...=equal_prj.htm

[rcubed]

All you need is a capacitor and a resistor to make a simple LPF. You can figure out the cutoff frequency here: http://www.muzique.com/schem/filter.htm

[dannybuoy]

LPF's tend to have a steep dropoff at the selected frequency. The further up you go past the cutoff frequency, the steeper the rolloff, on a graph it would look like a cliff edge. Shelving EQs (if set to cut and not boost) will have a similar rolloff up to a point but will then plateau out so that all fequencies above that point will be reduced by the same amount of dB. On a graph it'll look like a straight line, or a shelf.

[slyjoe]

Try this for determining values:
http://ourworld.compuserve.com/homep...wden/opamp.htm

[Nyarlathotep]

Originally Posted by rcubed

All you need is a capacitor and a resistor to make a simple LPF. You can figure out the cutoff frequency here: http://www.muzique.com/schem/filter.htm

Interesting..... So you can change the resistor or the cap.... *evil laugh*

Thank you very much

quick edit: I noticed that its for a 6db/oct filter. Any sites for stuff higher, like 15 or 30+?

I'd look it up myself, but I gotta go to work. And tomorrows 4:20......

[slyjoe]

The muzique site linked shows a low pass and high pass PASSIVE filter. And they are NOT the circuit used in instruments due to the interaction with other elements such as volume controls and coils in the pickups.

15 or 30 dB high and low pass filters are going to take a lot more components - it seemed from the original post you were looking at active???

[dannybuoy]

Most basses have a passive LPF built into them - that's basically what your tone control is!

[JimmyM]

Originally Posted by dannybuoy

Most basses have a passive LPF built into them - that's basically what your tone control is!

I was just about to say...does nobody use knobs anymore?

Last night I had a gig where I thought I was too trebly...turned down the tone knob on the bass about 1/3...perfect!

[slyjoe]

The tone control in a passive bass functions as a low pass filter (with some nuances) as danny and jimmy said, but the circuit is not configured as a LPF as illustrated at the muzique site.

The LPF shown has a series resistor with a shunt capacitor. Tone circuits in instruments have a resistor (variable) in series with a capacitor; they are both shunted across the output. The only time they are equivalent is when the resistance = 0.

Put that LPF circuit in your bass and you will get a much different response than a typical tone control you are familiar with.

[JimmyM]

Originally Posted by slyjoe

The tone control in a passive bass functions as a low pass filter (with some nuances) as danny and jimmy said, but the circuit is not configured as a LPF as illustrated at the muzique site.

The LPF shown has a series resistor with a shunt capacitor. Tone circuits in instruments have a resistor (variable) in series with a capacitor; they are both shunted across the output. The only time they are equivalent is when the resistance = 0.

Put that LPF circuit in your bass and you will get a much different response than a typical tone control you are familiar with.

It isn't going to make a lick of difference to me when playing "Blue Moon"

[slyjoe]

Originally Posted by JimmyM

It isn't going to make a lick of difference to me when playing "Blue Moon"

HAH - you're right. Unless you're putting that circuit into your bass.

[Nyarlathotep]

Originally Posted by slyjoe

15 or 30 dB high and low pass filters are going to take a lot more components - it seemed from the original post you were looking at active???

Sorry for not replying yesturday (the earliest I could get on after you posted).... but it was 420....

Anyways, yes Im looking for a schem for an adjustable freq sharp slope LPF. Im guessing thats active

There was a schem for a 36dB/oct LPF @ 1Khz in the PDF I linked. Im wondering what resistors I could switch out for pots, or resistor+pots, to get a range of freqs on it. Im thinking something like 20-2000Hz for the corner freq.

[HogieWan]

LPFs cut out everything above the selected frequency (after a somewhat steep dropoff), but a shelf cuts (or boosts) everything above that freq equally. Think hill vs plateau.