How to make your Jazzmaster tone controls useful

[Haustnótt]

Like everyone and his brother, I find the lower range of any stock tone control close to useless. It attenuates not only all treble, but most middle frequencies from your signal. The obvious cure to this is to change the tone control capacitor to one with less capacitance, to move the resonant peak and treble cutoff to more useful frequencies. Instead of doing things blindly, I did some calculations using a spreadsheet simulating a passive tone-volume circuit to see what would happen to the frequency response at different levels using different values of capacitance.

I used typical vintage JM pickup values, 3.5H inductance and 7,5kΩ DC resistance. Higher inductance will make the resonant peak taller and a little lower in frequency, higher resistance will lower the peak, but keep the resonant frequency.

It turned out the 1000K pots increase the resonant peak a lot with the tone control open, at 500K the peak is much lower, and at 250K there is no peak at all. So if you want your Jazzmaster to sound like one, you should keep the 1000K pots.

Lead circuit, stock (33 nF capacitor)
100% tone: +6db @ 5000Hz, -12db @ 13000Hz

10% tone: -1db @ 1000Hz, -12db @ 1850Hz

1% tone: -4db @ 650Hz, -12db @ 1500Hz

Strong peak in the low treble range with tone on full, very strong and early (200Hz) roll-off when tone control is closed, no resonant peak. This sounds very muddy.

So I suggest changing the capacitor to 10 nF. This will yield this result:

Lead circuit, modified (10 nF capacitor)
100% tone: +6db @ 5000Hz, -12db @ 13000

10% tone: 0db @ 1000Hz, -12db @ 10000 

1% tone: +3db @ 650Hz, -12db @ 2500

This is a very different result, the treble rolloff starts a lot higher. At zero tone, there will be a noticeable peak in the low midrange. This will make the whole range of the tone control useful, no mud at any setting.

If you go even lower in capacitance, you will introduce a strong peak with the closed tone control. Since the treble rolloff starts even higher and is somewhat slighter, this could function like a quite strong midrange boost:

Lead circuit, modified (4,7 nF capacitor)
100% tone: +6db @ 5000Hz, -12db @ 13000

10% tone: 0db @ 1000Hz, -12db @ 10000 

1% tone: +5db @ 1000Hz, -12db @ 2500

This gives almost identical result at almost closed tone, but makes the resonant peak less subtle, and pushes it up two thirds of an octave. Very noticeable.

Then there is the rhythm circuit. Because of the 50K tone pot, there is no peak at full tone at all, the tone rolls slowly off all the way from 40 Hz.

Rhythm circuit, stock (22 nF capacitor)
100% tone: -2db @ 1000Hz, -12db @ 6500

10% tone: +2db @ 400Hz, -12db @ 1250 

1% tone: +5db @ 450Hz, -12db @ 1150

Unlike the lead circuit, this has a resonant peak with tone reduced, but it is in the lower midrange, muddying things further up. So let’s move it upwards. I suggest changing the capacitor to 8.2 nF.

Rhythm circuit, modified (8.2 nF capacitor)
100% tone: -1db @ 1000Hz, -12db @ 6500

10% tone: +5db @ 750Hz, -12db @ 1800

1% tone: +8db @ 800Hz, -12db @ 1700

This pushes the resonant peak up almost an octave, and the treble rolloff half an octave. The mid boost will be quite extreme. Note that it also alters the tone at 100% a little, the rolloff starts somewhat later and the curve a tiny bit straighter, making the sound ever so slightly flatter.

In all cases, volume is on full. An amplifier impedance of 1MΩ is assumed, so is a cable capacitance of 100pF. All numbers are ballpark numbers, and your mileage may vary, as they say.

[PJazzmaster]

subscribed

[Whiny Minotaur]

Amazing, this should be stickied.

[Haddock]

Very interesting, as I'm not happy with the way my lead circuit behaves since I've replaced my pickups with AV65s in my CIJ Jazzy.

It turned out the 1000K pots increase the resonant peak a lot with the tone control open, at 500K the peak is much lower, and at 250K there is no peak at all. So if you want your Jazzmaster to sound like one, you should keep the 1000K pots.

Question : are you talking about the tone pot here ? I thought the volume pot was the one responsible for the strength of the resonant peak (higher resistance = more resonance), and the tone pot was responsible for the frequency where the peak is (higher resistance = higher frequency). Or is it the other way around ?

Asking because I find that at full volume, the resonant peak is too strong (that is, it sounds ice-picky at 100% tone and "honky" with the tone down) and I want a smoother sound, and was about to go to a 500k volume pot.

Thanks !

[Glimmer]

Hmm, hmm. Any audio samples?

[voided3]

I want to try this, thank you!

[jorri]

Very interesting, as I'm not happy with the way my lead circuit behaves since I've replaced my pickups with AV65s in my CIJ Jazzy.

It turned out the 1000K pots increase the resonant peak a lot with the tone control open, at 500K the peak is much lower, and at 250K there is no peak at all. So if you want your Jazzmaster to sound like one, you should keep the 1000K pots.

Question : are you talking about the tone pot here ? I thought the volume pot was the one responsible for the strength of the resonant peak (higher resistance = more resonance), and the tone pot was responsible for the frequency where the peak is (higher resistance = higher frequency). Or is it the other way around ?

Asking because I find that at full volume, the resonant peak is too strong (that is, it sounds ice-picky at 100% tone and "honky" with the tone down) and I want a smoother sound, and was about to go to a 500k volume pot.

Thanks !

they both are changing the impedance and react with picks and cables. However the tone control would also create a low pass filter so changing pot value would alter that in the same way as turning down. If you wanted to erase it i believe youd use no cap at all i.e. similar to volume pot on full 250k.

Also OP only had to look at the jag wiring its for all degrees of discernability the same. Although better is to wire a lag like the jm using only two pins of the pot.

i've tried 47 22 10 but apart from the occasional cocked wah sound of 10 i felt 33 was the perfect choice as i want it natural and not a cocked wah. 33seems finely tuned to suit a jm on full. Its subtle and the 22 maybe had better tones turned down but wasnt quite the perfect jm sound. 47 found to suck some mid details instead.

[taherbert]

I recently built a partsmaster with Curtis Novak JM-V/JM-Fat pups. I started out with the lead tone cap at 22 nF and rhythm circuit with 10nF based on the above recs. The lead tone pot (1Meg linear CTS) really didn’t do anything until it got down to 2 then it drops off to nothing, so I ended up putting the 33nF in there, now the taper is a little more friendly, starting to mellow out at 5.

I still found the rhythm circuit to be a little dark, even with the tone all the way up (50k fender pot, measures 51). I put a 47 Ohm resistor in series with the cap so the resistance goes from essentially 100k-50k (cause really, who needs the rhythm circuit darker?). Now, all the way up, it’s perfectly balanced between the bright lead circuit and darker old rhythm, and turned all the way down it sounds just like the stock rhythm circuit did before with the smaller cap value.

I also hated the way the volume on the rhythm circuit dropped off when the tone rolled down, looking at the schematic I see that the resistance between the volume pot wiper and the tone knob goes up as you turn down tone. I ended up soldering the tone circuit wiper to the volume wiper and now no volume drop with changes in tone knob.

I also changed the rhythm switch so that I can use all 3 pickup combinations with the rhythm circuit, and now I have pretty much my ideal jazzmaster wiring! This thing is amazing, I can get endless tone variations.

Edit:
In case anyone else wants to try these mods, I'm posting pics of another build I'm starting with the same wiring (except 500K pots) with a Lollar JM and Firebird pickup set.
Jazzmaster Mod Pics Folder