How does an EQ work?

[GreggBummer]

Forgive me if there is an existing thread, or this post is better served in another forum.

How does an average bass amplifier's equalizer work? Does it amplify the signal in each "band" of frequencies? Or, rather, does it filter them?

In regards to a graphic EQ (Like a Peavey Tour 450) or a varible graphic EQ (Like an SWR PB-200) they work something like this: I assume, and I am probably wrong, that the EQ will amplify the frequencies when the slider is moved above the flat postion (boost). It will not amplify, and will somehow reduce the frequencies when pushed below the flat postion (cut). Is this correct? When boosting, what part of the amp is actually amplifying the frequencies? The EQ itself? The pre-amp? The power-amp?

I realize that there are many different types of EQ's out there. Is there general groups? How do they work?

I don't have a background in electronics. However, I am willing to learn. Is there a primer somewhere that I can read?

I have the above named amps and I am finding that the best way to shape tone is with the EQ. I want to know more about how it works so that I can get more control over tone.

Thank you in advance.

Bummer

[sleepytime]

Originally Posted by GreggBummer

Forgive me if there is an existing thread, or this post is better served in another forum.

How does an average bass amplifier's equalizer work? Does it amplify the signal in each "band" of frequencies? Or, rather, does it filter them?

In regards to a graphic EQ (Like a Peavey Tour 450) or a varible graphic EQ (Like an SWR PB-200) they work something like this: I assume, and I am probably wrong, that the EQ will amplify the frequencies when the slider is moved above the flat postion (boost). It will not amplify, and will somehow reduce the frequencies when pushed below the flat postion (cut). Is this correct? When boosting, what part of the amp is actually amplifying the frequencies? The EQ itself? The pre-amp? The power-amp?

I realize that there are many different types of EQ's out there. Is there general groups? How do they work?

I don't have a background in electronics. However, I am willing to learn. Is there a primer somewhere that I can read?

I have the above named amps and I am finding that the best way to shape tone is with the EQ. I want to know more about how it works so that I can get more control over tone.

Thank you in advance.

Bummer

Typically, the knobs on an amp will boost or cut, at pre-determined frequencies, with the bass and treble being "shelving" controls, that is, they boost or cut all frequencies below a certain bass frequency, or above a certain treble frequency. The midrange(s) will be "peaking" controls, having the strongest effect at their center frequency and tapering off above and below that frequency.

Graphic EQ's are all peaking style cut and boost at several frequencies through the audio spectrum.

Semi-parametric EQ adds the ability to control the center frequency in addition to the level of the cut/boost.

Full parametric further adds the ability to control the "Q" (width) of the frequency band on each control, so you can boost a wide, smooth band for tone, or cut a narrow band to control feedback, for example.

Some tone controls are "passive" and they only cut levels, though amps with passive tone controls usually are not at all flat with all the tone controls maxed.

Just play with the knobs and sliders. It should be obvious what they are doing. It's usually best to start with tone controls at 12:00 and EQ sliders centered and go from there.

ETA: EQ is part of the preamp. Generally, anything that affects your sound is part of the preamp, where the signal levels are low. The power amp section is big and stupid. All muscle, no brains.

[GreggBummer]

Thanks sleepytime.

I am always fiddling with the EQ on my amp. I know what each slider does, but not the why or how.

When I make a boost adjustment, does the EQ "allow more signal to pass through" or does it "amplify that signal"?

Sorry, I'm having a hard time articulating what I am saying through the written word.

-B

[billfitzmaurice]

Originally Posted by GreggBummer

Forgive me if there is an existing thread, or this post is better served in another forum.

How does an average bass amplifier's equalizer work? Does it amplify the signal in each "band" of frequencies? Or, rather, does it filter them?

Active EQ amplifies each band; unity gain is flat, positive gain boosts, negative gain cuts. Passive EQ filters only.

[sleepytime]

Active EQ will involve a transistor, chip or tube stage while passive is just caps and resistors.

[JTE]

Originally Posted by GreggBummer

When I make a boost adjustment, does the EQ "allow more signal to pass through" or does it "amplify that signal"?

Sorry, I'm having a hard time articulating what I am saying through the written word.

-B

With active EQ you're amplifying the frequency band the control covers. With passive, when you turn up the bass knob, you aren't boosting the bass, but allowing more to pass.

John

[GreggBummer]

So, when I cut a particular set of frequencies... the pre-amp section is no longer amplifying them... or at least isn't amplifying them as much?

However, the power amp has nothing to do with the eq... it just amplifies whatever it is given.

Thanks for your help guys. Sorry to be so obtuse.

G

[greenboy]

You don't sound obtuse to me. Some guys never do figure out much about EQ.

[Mr. Foxen]

If you wanna learn more about valve amp/passive EQ, this will help: http://www.duncanamps.com/tsc/index.html