active and passive?

[musicofthemind9]

what is the difference between an active and a passive pickup? i probably already know the answer and i just dont realize it, but im not sure. thanx.

[hoerni]

Originally posted by musicofthemind9 what is the difference between an active and a passive pickup? i probably already know the answer and i just dont realize it, but im not sure. thanx.

 

The simplest definition is that active requires a power source (battery) and passive doesn't. The battery is required because active pickups include preamps (often built into the pickup casing but not always)

[musicofthemind9]

hmmmmmmmmm.....i thought it would be a little more complicated then that.

[Bacon86]

mmmmm, active pickups

[walfordr]

Active pickups are the same as passive pickups except they have a cheap, battery powered, solid state pre-amp added to your guitar.

 

Why anyone would want that is a mystery to me! Can anyone explain?

[eeka-chu]

Active pickups actively boost or buffer the signal that's being generated on their coil.

 

Like a tiny gain stage within the pickup if you like.

 

A buffer stage has a gain of 1. So the signal going in is the same as the signal going out. But a buffer stage can supply extra current to a signal path. That helps prevent the signal being distorted when power hungry effect inputs try to use up the very small current being generated by the pickups coil to drive their internal signal path.

 

A passive pickup is just a coil of wire that works purely by what is done to it, rather than what's done to it and what it does.

 

To convert a passive pickup to an active pickup just put a boost pedal between you guitar and amp, it's doing exactly the same thing. All be it externally.

 

But you can remove the pedal or change it. Unless you want to dig through the potting compound in something like an EMG you can't change the gain stage within it.

[eeka-chu]

Originally posted by walfordr Why anyone would want that is a mystery to me! Can anyone explain?

 

Because it gives you "Mad chuggin' soundz!", you fool!

 

Just kidding!

 

David Gilmour uses active pickups to drive the ungodly signal path through the unending labyrinth of effects he uses (used?).

[eeka-chu]

Because I love you, I even found you a picture of the kind of thing you'd use to create such an effect to give you an idea of how small they can be.

 

 

Retail on these amplifiers from National is about $0.50 maximum.

 

Oh yeah, the one I'm talking about is the tiny IC on the right of her finger tip, not the huge out dated IC on the left.

[walfordr]

Originally posted by eeka-chu Because it gives you "Mad chuggin' soundz!", you fool! Just kidding! David Gilmour uses active pickups to drive the ungodly signal path through the unending labyrinth of effects he uses (used?).

 

Yes, but as you said you can get the same effect, but better and more flexibly with a boost pedal or better still, by running the effects between your pre-amp and power amp. I still don't get it! People spend a {censored} load of money on "that tube sound" and drive the amp with a {censored}ty surface mount preamp.

 

I looked at EMG's site and found this rather classic quote:

 

"It's not really necessary for a pickup to have a magnet at all, but it helps."

 

Really!!!!

[dot-dot-dot]

 

Originally posted by walfordr {censored}ty surface mount preamp

 

 

Do I detect a bit of snobbery?

[eeka-chu]

 

Originally posted by walfordr "It's not really necessary for a pickup to have a magnet at all, but it helps." Really!!!!

 

 

He he he he! That's great!

 

It's totally down to marketing. Having it burried in the pickup helps save a bit of space I guess, but it could be in the control cavity or even the clip you put the battery into.

 

You could make a pickup without a coil if you were happy using solid state magnetic field detectors, but I seriously doubt many people would. They're only really made for measuring amps of juice going through power cables.

 

I think what's better is the price. For what is a few $'s worth of parts people are willing to pay a big chunk more.

 

I've spent a massive amount of time researching why people like the sound of valve components over solid state.

 

It all comes down almost solely to how the stage clips and distorts a signal. Provided the stage is running in perfect Class-A1 it's very hard to tell solid state and valve components apart. If possible at all.

 

The reason even audiophiles, who are supposidely running in Class-A1, can tell them apart is that the amp isn't always perfectly in Class-A1. From time to time it's going to distort in some way or another and then they can detect the obviously super inferiority of the product.

 

Audiophiles who still use valves are realistic. They know it's going to clip or distort at some point, so why not have it do it in a way that's at least pleasing.

 

It always amused me that people would liken the Tube Screamer to a warm valve sound when it's a solid state op-amp doing all the amplifying in it.

 

As far as solid state being junk because it's just 'sand', valves are just vacuums. There's nothing magical about them. The doped silicon in semiconductors can be made to be orders of magnitude more conductive than any valve's I know of.

 

Semiconductor foundries use literally millions of gallons of high purifity water each day to wash the silicon crystals clean.

 

But yeah.... you can do anything an EMG can do with a boost pedal.

[walfordr]

 

Originally posted by dot-dot-dot Do I detect a bit of snobbery?

 

 

Not at all, I have an open mind and am happy to embrace technology (eg I have a digital modelling amp which I find very handy), but I really just cannot see any advantages to active pickups. I'd be happy for someone to enlighten me.

[dot-dot-dot]

Originally posted by walfordr Not at all, I have an open mind and am happy to embrace technology (eg I have a digital modelling amp which I find very handy), but I really just cannot see any advantages to active pickups. I'd be happy for someone to enlighten me.

 

Okyay.

 

I just think saying "{censored}ty surface mount pre-amp" sounds a little uninformed - while the ones in EMGs could, for all I know, be the cheapest crap out there, a Burr-Brown op-amp in an SMD package is a device of great audiophile potential.

 

My apologies if I've read your statement as more of a generalisation than it was.

[eeka-chu]

It might be cool to make a generic PCB and then stick 10, 20 or 30 different opamps on it and a selector switch.

 

Since guitarists purposefully drive amplifier stages into distortion most of the time we should be able to hear the differences between them even more easily than the audiophiles claim to be capable of.

 

At $0.20 to $0.50 per opamp, it shouldn't be too expensive either.

[eeka-chu]

Originally posted by dot-dot-dot Okyay. I just think saying "{censored}ty surface mount pre-amp" sounds a little uninformed - while the ones in EMGs could, for all I know, be the cheapest crap out there, a Burr-Brown op-amp in an SMD package is a device of great audiophile potential. My apologies if I've read your statement as more of a generalisation than it was.

 

Is Moneky FX your page ...?

 

If so, it looks pretty cool!

[dot-dot-dot]

It is, yes. And thank you!

 

As for the selector idea, someone somewhere (diystompboxes maybe) did make such a thing, and I know Andy at Cruachan Audio has done some op-amp comparisons. The biggest difference seems to be the noise level, but after that I think the TL072s tend to sound best in dirt pedals. I like 4558s because I think that's a nicer number than 072.

[walfordr]

Originally posted by dot-dot-dot Okyay. I just think saying "{censored}ty surface mount pre-amp" sounds a little uninformed - while the ones in EMGs could, for all I know, be the cheapest crap out there, a Burr-Brown op-amp in an SMD package is a device of great audiophile potential. My apologies if I've read your statement as more of a generalisation than it was.

 

No offense taken at all and sorry if I seem ill-informed, but I still don't see the point. There is nothing "audiophile" about the electric guitar amplifier. Tubes are used in guitar amplifiers because of their non-linear characteristics not because they are capable of accurately amplifying a signal, the power supplies are designed to sag under heavy load thereby driving the power tubes further into their non-linear region, the output transformers are designed to saturate adding further signal colouration and the speakers are designed to innacurately reproduce the input signal and "break up" at high volumes.

 

I have no illusions that putting a well designed, broad spectrum amplifier into this signal chain is in any way detrimental to the "sound". My question is simply, why put a preamp in your guitar? It just seems the least flexible option to me.

[No Soul]

 

Originally posted by walfordr No offense taken at all and sorry if I seem ill-informed, but I still don't see the point. There is nothing "audiophile" about the electric guitar amplifier. Tubes are used in guitar amplifiers because of their non-linear characteristics not because they are capable of accurately amplifying a signal, the power supplies are designed to sag under heavy load thereby driving the power tubes further into their non-linear region, the output transformers are designed to saturate adding further signal colouration and the speakers are designed to innacurately reproduce the input signal and "break up" at high volumes. I have no illusions that putting a well designed, broad spectrum amplifier into this signal chain is in any way detrimental to the "sound". My question is simply, why put a preamp in your guitar? It just seems the least flexible option to me.

 

 

Louder, more pronounced attack, less noise, clarity, more sustain etc etc etc. Lots of great reasons to use actives. If you dont like those things, hey dont use em! Could you do all that with pedals? Sure, if you wanna buy all all those pedals, even at that, the voicing wont be the same as active pickups.

[dot-dot-dot]

Originally posted by walfordr No offense taken at all and sorry if I seem ill-informed, but I still don't see the point. There is nothing "audiophile" about the electric guitar amplifier. Tubes are used in guitar amplifiers because of their non-linear characteristics not because they are capable of accurately amplifying a signal, the power supplies are designed to sag under heavy load thereby driving the power tubes further into their non-linear region, the output transformers are designed to saturate adding further signal colouration and the speakers are designed to innacurately reproduce the input signal and "break up" at high volumes.

 

All true; I was responding (mostly) to the "{censored}ty..." bit of your post.

 

I have no illusions that putting a well designed, broad spectrum amplifier into this signal chain is in any way detrimental to the "sound". My question is simply, why put a preamp in your guitar? It just seems the least flexible option to me.

 

As I understand it, EMGs really came about because older amps didn't have much in the way of distortion - unless you slammed the front end with a big signal. EMGs let you put out a huge signal that'd get you far more distortion, and would also drive really, really long cables without degredation.

 

I believe that the active setup also means you can have much "weaker" pickups, which consequently have less pull on the strings. Plus they still sound the same even in a crap guitar (though I'm not sure how much that is myth and how much it's true).

 

I've never had them, and only briefly used a guitar with them. It was ok.

 

More generally, while I personally agree that building the preamp into the pickups seems rather limiting, I can think of a couple of reasons for having a pre-amp in the guitar itself. The main one, though, is that if you want to have long cables, buffering inside the guitar means you get the minumum possible signal loss over those cable runs - running through the cable first isn't as good for that purpose. 'Course, at that point you're probably better off with a decent wireless (if such a thing exists).

[walfordr]

Originally posted by dot-dot-dot All true; I was responding (mostly) to the "{censored}ty..." bit of your post.

 

Yep sorry. That didn't help my cause. I personally find this an interesting discussion!

 

As I understand it, EMGs really came about because older amps didn't have much in the way of distortion - unless you slammed the front end with a big signal. EMGs let you put out a huge signal that'd get you far more distortion, and would also drive really, really long cables without degredation. I believe that the active setup also means you can have much "weaker" pickups, which consequently have less pull on the strings. Plus they still sound the same even in a crap guitar (though I'm not sure how much that is myth and how much it's true).

 

Wouldn't you get the same effect by lowering your pickups and boosting the signal off guitar. I like to be able to adjust my pickups and actually get some string pull for some music. Jazz/Funk rhythm playing for example. I don't always want sustain.

 

More generally, while I personally agree that building the preamp into the pickups seems rather limiting, I can think of a couple of reasons for having a pre-amp in the guitar itself. The main one, though, is that if you want to have long cables, buffering inside the guitar means you get the minumum possible signal loss over those cable runs - running through the cable first isn't as good for that purpose. 'Course, at that point you're probably better off with a decent wireless (if such a thing exists).

 

You'd need a pretty long cable run though for this to matter though. Unless you have really crap capacative cable I don't thing anything less than 100m or so would be noticed.

 

As to the wireless discussion - that's a complete rant in itself!

[hoerni]

 

Originally posted by walfordr Yep sorry. That didn't help my cause. I personally find this an interesting discussion! Wouldn't you get the same effect by lowering your pickups and boosting the signal off guitar. I like to be able to adjust my pickups and actually get some string pull for some music. Jazz/Funk rhythm playing for example. I don't always want sustain. You'd need a pretty long cable run though for this to matter though. Unless you have really crap capacative cable I don't thing anything less than 100m or so would be noticed. As to the wireless discussion - that's a complete rant in itself!

 

 

You actually should be able to notice the difference between 10 and 20 feet of cable. I used to think it was silly myself until I did some SPICE simulations.

 

From what I could find, 300pF per foot is a good rule of thumb for guitar cable. Therefore a 10ft is 3nF and and 20ft cable is 6nF.

 

When the volume is rolled down (I check at about 10% or about 5 on the volume knob), the increase in capicitance can have a significant affect on the high frequency components when the tone knob is at 10.

 

Let me know if you want the simulation files (it's in an Orcad demo file)

 

Pickups have really high source impedances and easily loaded. That's why a buffer can make sense.

 

Then again, Hendrix supposedly preferred curly cables because of their increased capacitance(and it's affect on his tone). Whatever works.

 

Active pickups seem to be much more popular with bass players where they want the high frequencies from slapping and popping to come through un-attenuated. Horn drivers are also more common in bass cabs for the same reason.

[dot-dot-dot]

Originally posted by walfordr Wouldn't you get the same effect by lowering your pickups and boosting the signal off guitar. I like to be able to adjust my pickups and actually get some string pull for some music. Jazz/Funk rhythm playing for example. I don't always want sustain.

 

Well, I'm not really into active pickups, so I'm not the best person to ask! It doesn't sound like you'd like them though.

 

Originally posted by walfordr You'd need a pretty long cable run though for this to matter though. Unless you have really crap capacative cable I don't thing anything less than 100m or so would be noticed.

 

It also depends on what you're going in to - there are amps out there (so I've been told) with pretty low input impedances. You also need to remember that a simple cap/resistor model (for the cable and the input of the amp) misses the point - there's the pickup's own internal resistance and inductance to account for, so you end up with more of a resonant response than a simple low-pass.

 

Originally posted by hoerni From what I could find, 300pF per foot is a good rule of thumb for guitar cable.

 

 

I'd venture to suggest that that's a pretty crappy cable - music store "own brand" maybe. The Klotz/Sommer I use is 60pF/m - so about 20pF/ft.

[hoerni]

Originally posted by dot-dot-dot I'd venture to suggest that that's a pretty crappy cable - music store "own brand" maybe. The Klotz/Sommer I use is 60pF/m - so about 20pF/ft.

 

 

You might be right. I'll need to check what source I got that number from. I just checked the Canare website, and their guitar cable is only 49pF/ft.

[Milkman1]

^^

 

"Active pickups are the same as passive pickups except they have a cheap, battery powered, solid state pre-amp added to your guitar. "

 

--------------------------------------------------------------------------------

 

That's a pretty dismissive remark. Is it based on first hand experience or just what you've read somewhere?

 

 

EMGs are amazing pickups. There's nothing cheap about them. Contrary to popular misconception, they are vibrant dynamic pickups with tons of output. They clean up exceptionally well and interact perfectly with processing devices.

 

 

THAT's why someone would consider using them.

 

 

EMGs rock.

 

 

 

Milkman

[walfordr]

 

Originally posted by dot-dot-dot It doesn't sound like you'd like them though.

 

 

Actually I've never tried one either! Can't see why I would bother.

 

It also depends on what you're going in to - there are amps out there (so I've been told) with pretty low input impedances. You also need to remember that a simple cap/resistor model (for the cable and the input of the amp) misses the point - there's the pickup's own internal resistance and inductance to account for, so you end up with more of a resonant response than a simple low-pass.

 

 

Mmm hadn't thought of that. Just did a rough coupling circuit calculation, but I can't imagine there are many amps with an input impedence below 1M though. If there are - why?

 

 

Originally posted by Milkman1 That's a pretty dismissive remark. Is it based on first hand experience or just what you've read somewhere?

 

 

It's not really disputable. They are magnetic poles with a coil of wire wrapped around them (the same as passive pickups) with a cheap (as in low production cost) battery powered solid state pre-amp added. Nothing more and nothing less.

 

EMGs are amazing pickups. There's nothing cheap about them. Contrary to popular misconception, they are vibrant dynamic pickups with tons of output. They clean up exceptionally well and interact perfectly with processing devices.

 

 

I did not say EMGs are cheap. There are also passive pickups that are not cheap. If you like them, great!