Intriguing Question About Caps/inductors

[AndrewCE]

What effect would there be if you put an inductor in series with your pickup (assuming a one pickup guitar)? I'm guessing it would increase the impedance and take away highs, but how would it act differently than using a capacitor to shunt to ground (like most tone controls)?

[bluesy]

What effect would there be if you put an inductor in series with your pickup (assuming a one pickup guitar)? I'm guessing it would increase the impedance and take away highs, but how would it act differently than using a capacitor to shunt to ground (like most tone controls)?

Me again yes it would act pretty much the same as a cap shunt to ground. It's another way to make a single pole low pass filter. It's not usually done this way in production because caps are cheaper and lighter than inductors.

[AndrewCE]

What effect would there be if you put an inductor in series with your pickup (assuming a one pickup guitar)? I'm guessing it would increase the impedance and take away highs, but how would it act differently than using a capacitor to shunt to ground (like most tone controls)?

Me again yes it would act pretty much the same as a cap shunt to ground. It's another way to make a single pole low pass filter. It's not usually done this way in production because caps are cheaper and lighter than inductors.

It just seems like it would act differently. In the series inductor, youve got a "traffic jam" of high frequencies. But in the shunting capacitor, you have a "rerouting" of highs; they don't build up, they get released instead.

side question: To remove lows, do they usually put a series capacitor, or do they use an inductor to shunt to ground?

Also, why dont they make volume controls in this series way? Instead of putting a variable cap to ground, put a variable cap right in between pickup and output jack. This might actually be better, since when Vol is at "10", the pot has absolutely no effect on the signal.

[bluesy]

It just seems like it would act differently. In the series inductor, youve got a "traffic jam" of high frequencies. But in the shunting capacitor, you have a "rerouting" of highs; they don't build up, they get released instead.

side question: To remove lows, do they usually put a series capacitor, or do they use an inductor to shunt to ground?

Also, why dont they make volume controls in this series way? Instead of putting a variable cap to ground, put a variable cap right in between pickup and output jack. This might actually be better, since when Vol is at "10", the pot has absolutely no effect on the signal.

Yes, to remove lows, essentially a series cap is used - google "high pass" filter.

Not sure what you mean in that last paragraph. A volume control is a potential divider, i.e. a device that takes an input voltage (signal in this case) and provides, as it's output, some fraction of that signal. When a pot is at 10, it is not supposed to have an effect on the signal, because you have asked for 100% of the signal to be let through.

[AndrewCE]

It just seems like it would act differently. In the series inductor, youve got a "traffic jam" of high frequencies. But in the shunting capacitor, you have a "rerouting" of highs; they don't build up, they get released instead.

side question: To remove lows, do they usually put a series capacitor, or do they use an inductor to shunt to ground?

Also, why dont they make volume controls in this series way? Instead of putting a variable cap to ground, put a variable cap right in between pickup and output jack. This might actually be better, since when Vol is at "10", the pot has absolutely no effect on the signal.

Yes, to remove lows, essentially a series cap is used - google "high pass" filter.

Not sure what you mean in that last paragraph. A volume control is a potential divider, i.e. a device that takes an input voltage (signal in this case) and provides, as it's output, some fraction of that signal. When a pot is at 10, it is not supposed to have an effect on the signal, because you have asked for 100% of the signal to be let through.

i know what a high pass filter is, but there are two ways to make it, either with a series cap or a parallel inductor

oops i accidentally said "variable cap" but i meant "variable resistor"

A volume control actually does have an effect on the signal at 10, though. Just like a tone control bleeds off some highs at 10, volume control bleeds off volume. Because it's impossible for the volume pot to have infinite resistance (unless its a no load pot). A series pot would be able to have 0 resistance and therefore you wouldnt lose any signal.

[bluesy]

i know what a high pass filter is, but there are two ways to make it, either with a series cap or a parallel inductor

oops i accidentally said "variable cap" but i meant "variable resistor"

A volume control actually does have an effect on the signal at 10, though. Just like a tone control bleeds off some highs at 10, volume control bleeds off volume. Because it's impossible for the volume pot to have infinite resistance (unless its a no load pot). A series pot would be able to have 0 resistance and therefore you wouldnt lose any signal.

OK, you asked what they usually do - and the answer is, series capacitor.

The Volume pot should be a large enough value, compared to the other impedances in the circuit - like pickup impedance and amplifier input impedance, that is has no appreciable effect when set to it's maximum. Most other impedances in the circuit are 10's of k (like the 50k input on a guitar amp), hence volume pots are 250k or 500k. Being an order of magnitude bigger, it's effect should be small. So small, that the small loss is swamped by variations in gain in all sorts of other places in the guitar pedals and amplifier.

A series pot would indeed let 100% through at full volume, but it would have another serious problem. At zero, there would still be some sound because it cannot have infinite impedance. In fact, for a 500k pot into a 50k amp input, you'd get approx. 10% of the signal voltage still coming through. The design decision is that it is better to be able to turn it all the way down.

[AndrewCE]

i know what a high pass filter is, but there are two ways to make it, either with a series cap or a parallel inductor

oops i accidentally said "variable cap" but i meant "variable resistor"

A volume control actually does have an effect on the signal at 10, though. Just like a tone control bleeds off some highs at 10, volume control bleeds off volume. Because it's impossible for the volume pot to have infinite resistance (unless its a no load pot). A series pot would be able to have 0 resistance and therefore you wouldnt lose any signal.

OK, you asked what they usually do - and the answer is, series capacitor.

The Volume pot should be a large enough value, compared to the other impedances in the circuit - like pickup impedance and amplifier input impedance, that is has no appreciable effect when set to it's maximum. Most other impedances in the circuit are 10's of k (like the 50k input on a guitar amp), hence volume pots are 250k or 500k. Being an order of magnitude bigger, it's effect should be small. So small, that the small loss is swamped by variations in gain in all sorts of other places in the guitar pedals and amplifier.

A series pot would indeed let 100% through at full volume, but it would have another serious problem. At zero, there would still be some sound because it cannot have infinite impedance. In fact, for a 500k pot into a 50k amp input, you'd get approx. 10% of the signal voltage still coming through. The design decision is that it is better to be able to turn it all the way down.

good point in that last paragraph. it makes me wonder if theres a way to have the best of both worlds. i'll get to drawing for now

[psw]

There are mid-filter like controls and others (varitone) that use inductors...all such systems appear to be loss inducing...a tone control is generally rarely used and some seem to be of the impression that it adds "tone" especially if some mojo infused vintage cap is involved.

The answer is simple, but few want to hear it...put a battery and a transparent buffer in the thing...eliminate not only the losses in the guitar circuit be the significant losses and capacitance of the lead too...problem solved. But then, many don't want to contemplate that.

If, however you did add electronics into the guitar, you could get real boosting and tone shaping filters relatively easily, but I expect even with that capability, few would use it and it does kind of duplicate the eq stage of the amp...also underutilized as well.

One of the big drawbacks of putting an inductor into the guitar is that it is a coil...as such, you are adding effectively an antenna to attract hum! On a quiet guitar, you are effectively adding another single coil (albeit small) with the risk of more noise as opposed to a cap that often will filter out the very high frequencies where noise most commonly is, without the risk of adding noise...

Still...if you want to try it, no harm there I suppose, but as a basic idea I think bluesy has given more technical reasons...but if you step back a little, there is a flaw in the concept and looking for a novel approach to something that seems not to require a better solution.

But, hey...maybe I am missing something...

[AndrewCE]

Still...if you want to try it, no harm there I suppose, but as a basic idea I think bluesy has given more technical reasons...but if you step back a little, there is a flaw in the concept and looking for a novel approach to something that seems not to require a better solution.

But, hey...maybe I am missing something...

well i wasnt suggesting the use of an inductor over a capacitor just for the possibility of that mod, i also wanted to learn a little more about what inductors and caps do. i've read all i can find, and i know how they work and what they do, but thinking creatively is often the best way to familiarize oneself with a subject. i'm just thinking outside the box here. finding another way to do the exact same thing seems pointless, but it can actually be pretty interesting. heck, i saw a book once with 200 different proofs of the pythagorean theorem! pointless, but with it you can study how all the fields of math relate to one another.

[Paul Marossy]

As a passive circuit, an inductor with a series cap is more like a notch filter. If you want to play around with something interesting and make a resonant filter using an inductor, you could take the standard inductor based wah circuit and have an on-board "Q" filter kind of like what I did on my "SpankenStrat" - http://www.diyguitarist.com/Guitars/SuperStrat.htm

[AndrewCE]

As a passive circuit, an inductor with a series cap is more like a notch filter. If you want to play around with something interesting and make a resonant filter using an inductor, you could take the standard inductor based wah circuit and have an on-board "Q" filter kind of like what I did on my "SpankenStrat" - http://www.diyguitarist.com/Guitars/SuperStrat.htm

you mean like put just a cap and inductor in series (or in parallel, shunting to ground) to make a bandpass filter? to cut out the highs and lows? is that what you mean?

[Paul Marossy]

As a passive circuit, an inductor with a series cap is more like a notch filter. If you want to play around with something interesting and make a resonant filter using an inductor, you could take the standard inductor based wah circuit and have an on-board "Q" filter kind of like what I did on my "SpankenStrat" - http://www.diyguitarist.com/Guitars/SuperStrat.htm

you mean like put just a cap and inductor in series (or in parallel, shunting to ground) to make a bandpass filter? to cut out the highs and lows? is that what you mean?

I was thinking of it more as a tone control, using a cap an inductor in series to ground. Essentially, it's the Gibson "Varitone" circuit: http://www.blueshawk.info/varitone.htm

I like the on-board adjustable "Q" filter (wah) idea. That way, I get a resonant filter in conjunction with having all of the tone controls I am used to.

[AndrewCE]

As a passive circuit, an inductor with a series cap is more like a notch filter. If you want to play around with something interesting and make a resonant filter using an inductor, you could take the standard inductor based wah circuit and have an on-board "Q" filter kind of like what I did on my "SpankenStrat" - http://www.diyguitarist.com/Guitars/SuperStrat.htm

you mean like put just a cap and inductor in series (or in parallel, shunting to ground) to make a bandpass filter? to cut out the highs and lows? is that what you mean?

I was thinking of it more as a tone control, using a cap an inductor in series to ground. Essentially, it's the Gibson "Varitone" circuit: http://www.blueshawk.info/varitone.htm

I like the on-board adjustable "Q" filter (wah) idea. That way, I get a resonant filter in conjunction with having all of the tone controls I am used to.

oh so basically the opposite of a wah; instead of resonant peak there would be a resonant valley; it's a mid-cut control

i was wondering why you would put a passive wah-filter on your guitar. that would take away so much volume!

[psw]

Just so people are clear on this...in a passive circuit you can not "boost" tone...you can only cut frequencies.

One area that seems to be under appreciated for what it is, is the combining of pickups and strategies like phase shifting. These are filter effects using the existing inductors of the pickup coils to shape tone to a great extent.

So, you want a mid scooped tone on the bridge pickup...you can get that on a strat by combining the bridge and middle at selection 4...want the reverse response, try reversing the phase. Put two pickups in series (say middle and neck) and you do get a mid boost and more power. Use a filter cap or tone control on one of these pickups and you can tone shape this further by combining and cancelling various amounts of the secondary boosted coils.

Most of this with the creative use of the existing coils in a guitar (multiple pickups) without adding more noise and filtering inductors into the machine.

There are such tone controls...perhaps look at what torres engineering and others offer...or the varitone circuits...but often they less than live up the the hope and hype and always as passive circuits they "cut" and are such not tone "enhancers"...

[Paul Marossy]

oh so basically the opposite of a wah; instead of resonant peak there would be a resonant valley; it's a mid-cut control

i was wondering why you would put a passive wah-filter on your guitar. that would take away so much volume!

Yeah, I guess you could say that it is a mid-cut control. The wah circuit on my guitar is a Maestro Boomering clone on a compact PCB that I designed. It's not a passive circuit, it runs on a 9V battery.