Inductor on tone pot?

jonfoote · Post by **jonfoote** » 04 Aug 2010, 08:31

search for duncans amp tools for lots of tone shaping goodness.

swampnoise · Post by **swampnoise** » 06 Aug 2010, 14:49

You could use a series (R) LC circuit from signal to ground, like a bill Lawrence Q filter or a Gibson varitone. This will give you a passive midcut.
It works best with quite a large value inductor and a small value capacitor. If you have the space inside your guitar you could even use a cheap humbucking pickup with the magnets removed as an inductor.
Frequency of LC circuit is f=1/2pi * squareroot LC

TDR1138 · Post by **TDR1138** » 06 Aug 2010, 16:45

swampnoise wrote:You could use a series (R) LC circuit from signal to ground, like a bill Lawrence Q filter or a Gibson varitone. This will give you a passive midcut.
It works best with quite a large value inductor and a small value capacitor. If you have the space inside your guitar you could even use a cheap humbucking pickup with the magnets removed as an inductor.
Frequency of LC circuit is f=1/2pi * squareroot LC

Awesome, thanks. I read somewhere that a 1.5 Henry inductor was a good one to start with. Sound right? Also, what pot value should I use? I think I have a few 250k and 500k pots lying around. Would those work, or should I look for something else? Finally, does the order of the cap and inductor in the series matter (i.e. cap --> inductor --> ground versus inductor --> cap --> ground)?

Bear with me, I'm learning...

swampnoise · Post by **swampnoise** » 07 Aug 2010, 08:56

I would personally put the coil closest to ground and the cap closest to signal, but for frequency response this wouldn't matter.
A 250k or even a 500k should work fine here. 1.5H = the standard value for the gibson varitone. I wouldn't go any smaller than this. If I would want to do a low mid scoop for bass I'd be tempted to at least double that value. It has to do with Q factor.
See series RLC circuit on wikipedia for the equations.

TDR1138 · Post by **TDR1138** » 09 Aug 2010, 19:03

Awesome, thanks. I'll read up on the circuit and then I just have to find the time...

skylark44 · Post by **skylark44** » 23 Nov 2010, 06:04

Does anyone know what effect (if any) putting 150k ohm resistors, in parallel with the capacitors would have on tone? I'm not using an inductor one this build, but thought I'd try something different. Also, would it be better, tone-wise to put the resistor in series or not?(and why). Thanx, in advance.

phatt · Post by **phatt** » 23 Nov 2010, 13:29

Hi Skylark,
Not sure we are on the same schematic but except for bypass position the 100k is generally in *Series*.
It removes (or tries too) the hump before the mid dip ,,but as you are not using the inductor then it might not do much.
You really need to try different values of R as different PU's will yeild different tone response shapes anyway.
Phil.

skylark44 · Post by **skylark44** » 24 Nov 2010, 01:59

Thanx for the reply

...what would putting it in parallel do?

phatt · Post by **phatt** » 24 Nov 2010, 10:15

skylark44 wrote:Thanx for the reply ...what would putting it in parallel do?

Across the cap? then it would work less effectively.

At a guess; as the value of the R decreases then the cap is eventually shorted out and only the inductor would effect the tone shape.

My advice is throw the idea in the bin.

Phil.

skylark44 · Post by **skylark44** » 27 Nov 2010, 06:05

Sorry for asking so many nOOb questions, but...can you explain (in better detail) how this "hump" effects the tone?

Also, if I do end up using a resistor with the cap...should I use just one, connected to all of the caps...or put a resistor on each of them?

phatt · Post by **phatt** » 27 Nov 2010, 11:22

If you are not going to use an inductor then it's a waste of time
***No inductor = No mid dip, just treble cut***
Your tone pot already wipes treble.

Basic Varitone circuit;
The switch selects differing C values which moves the freq of the notch. The series R 100k in front of the LC bandpass can be made variable for a little control of notch width or humps.
**That is the resistor you need to play around with**

A 100k across the C of the LC circuit will just do nothing cept maybe adding to the overall loss of the circuit. it will pull down the output below the set freq but not above. Hint play with the Better idea above.
This stuff is not so hard to throw together so why not experiment and find out yourself.
It's all passive so just a few nails on a board and wire up a few components

Phil.

Post by **modman** » 27 Nov 2010, 12:13

I merged three topics on using inductors in the guitar's passive tone control.
If you find an existing thread on the same topic, asking your question there will fire off notification mails to all people who ever posted in that thread.

swampnoise · Post by **swampnoise** » 22 Apr 2011, 20:26

You need more than 1.5H on a bass to get to the desired low mid frequency. You could of course use the smaller coil value & a bigger value cap (using the previously stated math) but this sounds different than a bigger coil & smaller cap. This effect has nothing to do with frequency, but with the steepness of the filter.
Bill Lawrence makes a q-filter coil for bass, it has a higher inductance of 3H.

http://wildepickups.com/Q-filter.html

I used to do experiments like this using cheap humbucker coils with the magnets removed.

mictester · Post by **mictester** » 22 Apr 2011, 20:34

HydrozeenElectronics wrote:this sounds like a neat idea. Would I be able to get a Mid Range Boost using an inductor? I would like the boost centered on 500HZ.

Thanks

That would be best done using a simple bandpass stage. No inductors required! The simplest circuit would be a "Twin-T" filter, and you can alter the "Q" of the filter (the wideness of the bit that gets boosted) by changing the gain of the transistor in the filter. Really simple!

DrNomis · Post by **DrNomis** » 23 Apr 2011, 02:46

If you go to the Gyraf Audio Website, they have a DIY project for a Pultec Passive EQ, this uses Inductors and Capacitors to do the EQ-ing, but it has a Tube output section, very interesting project, and I might build a couple of them one day....

Aharon · Post by **Aharon** » 03 Jun 2011, 00:49

Had a Westone guitar with an inductor,I removed it....think it was connected to ground.Used it for a wah and it sounded great,that should give u an idea of the mH.
Aharon

Zipslack · Post by **Zipslack** » 03 Jun 2011, 19:50

I haven't seen particulars, but I haven't really searched either...

Try looking for the Westone Spectrum guitar controls...as the previous poster mentioned, they had a weird inductor tone system. My Spectrum 3 looks like it has a tone pot with a built-in inductor on the bottom. It does give some variations in the normal tone, but I've found it to be mostly useless. Maybe you should try a Vari-Tone control as an external box first before you start doing surgery on your guitar.

phatt · Post by **phatt** » 06 Jun 2011, 08:40

Zipslack wrote:I haven't seen particulars, but I haven't really searched either...

Try looking for the Westone Spectrum guitar controls...as the previous poster mentioned, they had a weird inductor tone system. My Spectrum 3 looks like it has a tone pot with a built-in inductor on the bottom. It does give some variations in the normal tone, but I've found it to be mostly useless. Maybe you should try a Vari-Tone control as an external box first before you start doing surgery on your guitar.

+ 100

Google *PhAbbTone* ,,, a Stand alone tone control ,,(powered by a 9volt battery) that works better than most Valve derived circuits.
Makes you wonder why no one thought of it before me?
Phil.