tone control

[Bone Tone]

Hi Guys, first post here.

I've just installed a JB jr in the bridge position of my Highway 1 as per the schematic, only to find that the tone control has no effect when the bridge pickup alone is selected, but when bridge/mid are selected tone works fine.

I've checked and re-checked my handiwork but can't see the problem... guess its right in front of me. :smack:

Any help would be appreciated.

 

[Artie]

Re: tone control

Hmmm . . . I'm pretty sure that thats standard Strat wiring. Two tone controls with one for the neck and one for the middle. I don't think you did anything wrong.

Use this diagram as a reference:

http://www.seymourduncan.com/website/support/schematics/3singlecoils_1vol_2tones.html

 

[sanrafael]

Re: tone control

ArtieToo pointed this out in another thread. The tone control loads the pickup a little bit, reducing the brightness. Not much, some (including me) would say, but the effect is there, and if you want the highest brighness (as you might on a bridge pickup), it is a bit brighter if there is no tone control. The strat appears to have been designed for maximum brightness.

 

[jon]

Re: tone control

I'm curious, my guitar HAD 2 volumes, no tone, I HAD a JB in the bridge but found it a little sharp and without much 'body' would a tone control make it a little softer, also, I had a coil tap on it, taking this away, will this help a bit?

 

[sanrafael]

Re: tone control

The tone control, in the full treble position, just acts as a resistor across the pickup. The resistor removes the effect of the capacitor since it is a large impedance compared to the cap. You can make a pickup less bright by putting additional resistance across it, and this might or might not be the effect you want. A value to start with would be a resistor equal to the value of the volume control. This would halve the total resistance, and would be a noticeable but not large effect. Smaller value resistors would dull it more.

I do not know about the coil tap.

You might want to check if the value of the volume control is the correct one for that pickup.

 

[Artie]

Re: tone control

The tone control, in the full treble position, just acts as a resistor across the pickup. The resistor removes the effect of the capacitor since it is a large impedance compared to the cap. You can make a pickup less bright by putting additional resistance across it, and this might or might not be the effect you want

Hey sanrafael; thats not exactly correct. What you're saying is true about a volume control, but not a tone control. A volume control at "10" is just a resistance across the pup, and making the value smaller will "load down", or suppress, the high end of the pup.

A tone control, on the other hand, is simply a high-frequency pipe to ground. The "size" of the pipe is determined by the resistance of the pot. The smaller the pot value, the bigger the pipe. A 250k pot is like a 500k set on "5". A 500k is like a 1 meg set on "5", and so on. But any pot value on "10" is still a certain degree of "pipe-to-ground". Eliminating the tone control completely, or using a "no-load" pot, is closing the pipe off totally.
Thats the "brightest" option.

 

[sanrafael]

Re: tone control

Well, I think what I am saying makes sense, but maybe I have misunderstood something.

When you place a resistance across a pup to damp the resonance, the significant effect is at frequencies near the resonance. If you place a series RC across the pup, and the impedance of the C at the resonant frequency is small compared to the resistance of the R, then the effect is essentially the same. For example, a .02 microfarad capacitor (typical of a tone control) has an impedance of 1592 at 5000 Hz. This is much smaller than 250K or 500K and so with either pot on 10, the series RC circuit would act almost like the resistor by itself.
I think that the operation of the usual guitar tone control is this: as you turn the pot from 10 down, at first the effect comes from loading the pickup with the decreasing resistor value. But as the pot value continues to decrease, the capacitor starts to matter. With the pot at zero, the capacitor drastically alters the resonant frequency of the pickup., but the damping is very high with this value of C because of the resistance of the pickup. (At 500 Hz, the impedance of the C might be 15,920, only somewhat greater than the resistance of many pickups.)

 

[Artie]

Re: tone control

I understand what you're saying, but I think where the confusion comes from is in this statement:

The tone control, in the full treble position, just acts as a resistor across the pickup.

A resistor, all by itself, across the p'up will "load" the entire frequency spectrum of the p'up. The cap, in series, causes the "load" to only affect a certain frequency range. For example, you can do a simple experiment where you take a 500k resistor in series with your .02uf cap, (which simulates a tone control on "10"). Place a switch across the cap so that you can short it out. You should hear a distinct difference in tone as you flip the switch, which, of course, indicates that there's quite a difference between a volume control "load", and a tone control "load".

Does this make sense? :question:

 

[sanrafael]

Re: tone control

That is a good experiment, but do you hear the distinct difference in tone when you do the experiment? The analysis says that you will not hear a significant difference. In a series combination, if one element has a much lower impedance than the other, as is the case here at resonance, the element with the low impedance cannot have much effect. It is hidden by the higher impedance element.
Also, the pickup has a lower impedance at lower frequencies. Thus it takes a lower impedance to have an effect. The resistor by itself has little effect at the lower frequencies; that is why it reduces the brightness, rather than causing an overall loss in level. The series combination cannot have any more effect unless the resistor is much reduced in value so that the pickup sees the capacitor.

 

[Artie]

Re: tone control

That is a good experiment, but do you hear the distinct difference in tone when you do the experiment?

Thats a good point. It was, in fact, a "virtual" experiment, with the conclusions gleaned from various volume and tone switching I've done in various guitars.

However, I believe its worthy of a "true" experiment. I just put my "test" guitar back together the other day, so give me a day or two to get this together. Might be interesting. I'll let you know.

 

[Kent S.]

Re: tone control

Well, I think what I am saying makes sense, but maybe I have misunderstood something.

When you place a resistance across a pup to damp the resonance, the significant effect is at frequencies near the resonance. If you place a series RC across the pup, and the impedance of the C at the resonant frequency is small compared to the resistance of the R, then the effect is essentially the same. For example, a .02 microfarad capacitor (typical of a tone control) has an impedance of 1592 at 5000 Hz. This is much smaller than 250K or 500K and so with either pot on 10, the series RC circuit would act almost like the resistor by itself.
I think that the operation of the usual guitar tone control is this: as you turn the pot from 10 down, at first the effect comes from loading the pickup with the decreasing resistor value. But as the pot value continues to decrease, the capacitor starts to matter. With the pot at zero, the capacitor drastically alters the resonant frequency of the pickup., but the damping is very high with this value of C because of the resistance of the pickup. (At 500 Hz, the impedance of the C might be 15,920, only somewhat greater than the resistance of many pickups.)

First of all approximating all values for practicality, a straight resistor will only really effect the amplitude of the pups res Fc peak, unless you get it very low in which it will start to decrease the output level voltage, of course we aren't talking about that. If you have a capacitor and resistor in series, and that series connection is placed in parallel with the pup (as we are talking here) ... then with a tone pot of 500k (if we assume a linear response to frequency) the the total added loading is the Xc of the cap plus the 500k of the pot. Now at 5kHz. we have (500k+1.6k) 501.6k, at 10kHZ, we have (500k+0.8K) 500.8k; going the other way, at 2.5kHZ. we have (500k+3.2k) 503.2k , and continuing down in octaves .. 506.4k, 512.8k, 525.6k, 551.2k,602.4k (ending at 78.125Hz., below the lowE'sfundamental Fc).
The difference in load on the pup changes with Fc, from 10kHz. (more isn't really practical for guitar) to slightly below the fundamental of the lowest note is 101.6k ... higher frequencies loaded more than the lower ones.
This results in the higher of the higher Fcs being attenuated more (I mean that is what a LPF does), the difference between the two is very subtle, a straight resistor serves to only dampen the pup's res Fc, the res Fc shift of the pup only happens a low levels of resistance (tone pot settings), as the resistance damps that peak, however in both cases once that resistance is low enough to to allow the res Fc shift it will do that ... BUT it also attenuates the Fcs above it, the -3dB corner remains the same regardless of the pup resonance with the cap, it will stay determined by the impedance of the source plus any controlling resistance (pot setting), which when to much will dampen that new res Fc peak (which will be below the cut-off Fc of the filter). What will not change is that when the control is moved it will shift both the corner -3dB Fc of the filter as well as it's lower corner Fc of the maximum attenuation shelf.
The difference at 10 is subtle at best, and shows up differently from pup to pup ... It is worth noting that they are not the same though ... If you were to find the pups res Fc, and place a resistor (R1) of some value there, then exchange that for a resistor (R2)in series with a cap whose R2+Xc equalled R1, then you'd find that the RC has a bit less overall brightness then the R alone (this effect becomes more noticeable depending where the pups res Fc peak is located, as pup's with high res Fc peaks may not be perceived as bright as some a bit lower).

 

[Kent S.]

Re: tone control

...........In a series combination, if one element has a much lower impedance than the other, as is the case here at resonance, the element with the low impedance cannot have much effect. It is hidden by the higher impedance element.

A series impedance is just that, series, the two are added together ... one doesn't mask the other ... In regard to a first order Low Pass Filter with limited
attenuation (in this case made variable by the tone pot's setting), you must investigate the effect of the secondary (controlling or attenuation level resistance) in conjunction with the source resistance {I realise we are actually talking about Z and not DCR, but it stands as is}, on the filter's shelves ... I'm not sure why you keep bringing resonance into this situation. The pup's resonance doesn't have anything to do with the effect of the filter with at this point.

Also, the pickup has a lower impedance at lower frequencies. Thus it takes a lower impedance to have an effect. The resistor by itself has little effect at the lower frequencies; that is why it reduces the brightness, rather than causing an overall loss in level. The series combination cannot have any more effect unless the resistor is much reduced in value so that the pickup sees the capacitor.

Well, like I stated before, the only thing the resistor alone does is pull down the amplitude of the res Fc peak, but it does not cause a high roll off slope like the filter does. By the time it gets to that point, the overall level starts to be effected as well and for the same reduction in high end, you would receive a tremendous loss of output voltage.

 

[Kent S.]

Re: tone control

I understand what you're saying, but I think where the confusion comes from is in this statement:



A resistor, all by itself, across the p'up will "load" the entire frequency spectrum of the p'up. The cap, in series, causes the "load" to only affect a certain frequency range. For example, you can do a simple experiment where you take a 500k resistor in series with your .02uf cap, (which simulates a tone control on "10"). Place a switch across the cap so that you can short it out. You should hear a distinct difference in tone as you flip the switch, which, of course, indicates that there's quite a difference between a volume control "load", and a tone control "load".

Does this make sense? :question:

As I stated in some other replies, I think the difference is subtle, and I think a lot of it is dependent on the pups used (their DCR,Z, and Res Fc{Xl = Xc} ).
A guitar with a 500k volume pot and a 250k tone control (with say a 223 cap), can sound the same as a guitar (same one no doubt) with a 250k volume and a 500k tone pot ... all at ten. It by no means mean that they will sound different, but they may, if so, it will be subtle. This is one of those instances were I think both parties might be in the right, it kinda becomes a matter of perspective. Regarding those numbers I issued in the first reply on this ... well even a difference of 1.6k is enough to make an audible difference in a tone knob setting.

 

[Kent S.]

Re: tone control

Thats a good point. It was, in fact, a "virtual" experiment, with the conclusions gleaned from various volume and tone switching I've done in various guitars.

However, I believe its worthy of a "true" experiment. I just put my "test" guitar back together the other day, so give me a day or two to get this together. Might be interesting. I'll let you know.

Just don't do that one until you get the other two tests done first, what's the status on the pot DCR vs Z test?

 

[Kent S.]

Re: tone control

Hi Guys, first post here.

I've just installed a JB jr in the bridge position of my Highway 1 as per the schematic, only to find that the tone control has no effect when the bridge pickup alone is selected, but when bridge/mid are selected tone works fine.

I've checked and re-checked my handiwork but can't see the problem... guess its right in front of me. :smack:

Any help would be appreciated.

BTW, Talk about getting off the subject with techno babble ... :laugh2:
Well, you can double check the schematics at ...
www.mrgearhead.net/faq/manuals.html
That being said, I believe, like Artie said, that the Highway 1 comes wired traditional strat ... i.e. no tone knob on bridge pup.
You can disconnect the wire from the middle pups tone control where is connects to the 5 way switch, and connect it to where the bridge pup connects directly, or move it one lug over if you want the middle to go without and have a tone control for the neck and one for the bridge and middle ...This is cool.
You can also just run a jumper wire from where the mid pups tone contol connects on the 5way to that empty lug, but keeping it connected where it is also. That gives you a tone for the neck pup, and one for both the middle and bridge pups. A lot of modern strats are wired that way now.

 

[Artie]

Re: tone control

Just don't do that one until you get the other two tests done first, what's the status on the pot DCR vs Z test?

Will do. :22:

BTW, Talk about getting off the subject with techno babble ...

Yup, poor ole Bone Tone is sitting back somewhere going WTF! :laugh2:

I've always wondered why the Strat didn't connect the two tones to the two end lugs of the 5-way. That would give you a tone control in every position except the middle, (which is probably a Strat's least used position), and the two controls would never interact with each other. I might try that on my Strat . . .

. . . after I do the Z-pot test, and the pup polarity test, and get Chi3f's drawing done, and do the tone/cap/switch experiment . . . :smack:

BTW - Part of the reason I couldn't do the Z-pot test is that I need to do that at work, and we just finished up a big ISO-9000 inspection. Now that things are settling down a bit, I should be able to get this done.

 

[Kent S.]

Re: tone control

Yup, poor ole Bone Tone is sitting back somewhere going WTF! :laugh2:

Yeah, but I think I got him straight ... :laugh2:

I've always wondered why the Strat didn't connect the two tones to the two end lugs of the 5-way. That would give you a tone control in every position except the middle, (which is probably a Strat's least used position), and the two controls would never interact with each other. I might try that on my Strat . . .

Yeah, the jumper to the middle/bridge works out pretty good, jumpering the neck/middle with a no-load, and then using a normal tone on the bridge only would be good as well (always wondered why they put the no-load on the brdige side and not the neck side, on some HB equipped bridges they put the no-load there ... ah that's not where I would want it). The neck tone, bridge tone, and none for middle does workout very well though. Plus it lets you save the middle alone position for an in between clean jangle type rhythm tone ... very good combo ... BTW I prefer that set up with a 500k volume pot, 250k no-load on neck pup, and 500k tone for bridge.

BTW - Part of the reason I couldn't do the Z-pot test is that I need to do that at work, and we just finished up a big ISO-9000 inspection. Now that things are settling down a bit, I should be able to get this done.

Oh, fun ... also I'm sure the acting supervisor would be curious about extra cirricular testings involving co/gov't equipment ... :laugh2:

 

[sanrafael]

Re: tone control

I did Artietoo's experiment this morning; used different values because my guitar has humbucker pickups with about half (not twice!) the impedance of a regular single coil pickup. It uses a 100K volume pot. The guitar circuit allows the tone control to be completely switched out. Thus this experiment can be done outside the guitar wuth the volume control al the way up.

Step 1. Verify what we pretty much agree on: Connect a resistor with a value equal to the value of the volume control (100K) across the output of the guitar. (The volume control is up all the way for this test, of course.) There is a distinct, but not large loss of brightness. This test is repeatable, and I think everyone would agree on the result.

Step 2. Put a .056 microfarad capacitor in series with the resistor. I am using a larger capacitor than mentioned above because the reistor has a smaller value.
Short/unshort the capacitor, and listen for the difference. There seems to be a small difference, but I would not bet my life on it. I do not hear it every time I short/unshort the cap, so maybe I am imagining it. Artietoo, may be you have better hearing than I do and can be more definite about it.

Kent, we agree on the series RC. When I say that the R hides the effect of the C, I just mean that changes in the impedance of the C with frequency have little relative effect on the overall series impedance when the R value is large compared to the C impedance. Just an intuitive way of looking at it, nothing more, and it only applies near the resonance because at really low frequencies the impedance of the C is huge.

 

[Artie]

Re: tone control

Step 1. Verify what we pretty much agree on: Connect a resistor with a value equal to the value of the volume control (100K) across the output of the guitar. (The volume control is up all the way for this test, of course.) There is a distinct, but not large loss of brightness. This test is repeatable, and I think everyone would agree on the result.

Hmmm . . . thats interesting. I would have thought the difference to be more significant. However, its possible that you didn't get more noticable results because of the 100k volume and tone control. I've never actually heard of a guitar that used values that low. Its possible that you're pre-loading the pickup so much as to be beyond the level of effectiveness.

I'm going to repeat the experiment, but with using 500k controls. It'll still take me a couple days to get this together, however.

 

[sanrafael]

Re: tone control

Hmmm . . . thats interesting. I would have thought the difference to be more significant. However, its possible that you didn't get more noticable results because of the 100k volume and tone control. I've never actually heard of a guitar that used values that low. Its possible that you're pre-loading the pickup so much as to be beyond the level of effectiveness.

I'm going to repeat the experiment, but with using 500k controls. It'll still take me a couple days to get this together, however.

Artietoo, I would have preferred to do this test with a standard guitar, too, but this is what I have. The pups are not heavily loaded; they are quite bright. I made the pups lower impedance because I wanted a guitar that does not lose highs when you turn down the volume. Obviously one can do this by just winding less wire on the two coils, but there is more to it. The big problem with pups is that the inductance depends almost on the square of the number of turns, while the output level depends almost linearly on the number of turns. Suppose you replaced one coil with two in series, each with half the number of turns, and also suppose you keep the same core/magnet structure. Also ignore coupling between the coils. Then you have about the same output level, but half the inductance.

Now in the real world, what you get is a four coil humbucker under a standard cover with less total wire because you have four cores taking up space (all use slugs, not screws). The impedance is lower than standard as I said; the output level is a bit less than a standard single coil, but the signal to noise ratio is better than standard with a solid state preamp, because solid state works really well with low impedance. These pups are not for tubes; I am trying to learn jazz, and a clean solid state sound is just fine. (Of course you could use an ss preamp with a tube amp in any case.)

Any way, I think the test is valid even with the different values, but I will wait for your results with patience, of course. (Actually, I have some heavy duty stuff coming up at work, and probably will not get here too much for the next week or so.)