The "balanced set", is to balance volume or tone?

[antigua]

Well I think I know the answer; to balance out the tone, and not really the volume. In general, the neck position is louder than the bridge, because the wider string movement over the neck pickup means there is more fundamental and lower harmonics amplitudes. So there are two "problems" with bridge pickup, they're too quiet and they're too bright. But I contend that a typical "balanced" set only addresses the fact that the bridge is too bright, and not that it's too quiet.



Crash course about balanced sets: pickup sets were not always "balanced", in the 50's and 60's they just used the exact same model of pickup for both the neck and bridge. "Balanced" sets are an innovation that didn't occur until the 70's or 80's.

Crash course on hearing sensitivity: the smallest SPL (sound pressure level) difference in sound a person can hear is about 1dB in ideal environments, and about 3dB in everyday noise situations. Here is a test file I made demonstrating the differences in decibel amplitudes. Note that if they all sound the same, your PC speakers are probably compressing the amplitude. As for frequency shifts, human hearing is much better in that respect, and it is said that people can distinguish frequency changes to within 1Hz. If two pickups attenuate treble at, say, 200Hz apart, this video can give you an idea of what those pitches actually area.


Now the evidence, I've made at least a dozen bode plots of lots of "balanced sets", where the bridge (and sometimes the middle) pickup is wound "hotter", with more winds of wire, in order to, according to various pickup making companies, to balance the volume output between the bridge and the neck pickup. In many of the plots, I measured the whole set in a single plot, loaded and unloaded, with a given voltage and testing procedure, so that the extent to which the "hotter" bridge (and or middle) pickup to be louder than the neck pickup is revealed in the plots by virtue of how far apart the plot lines are on the vertical dBV scale. 

While answering a question on another forum, it dawned on me that it's actually rather unusual for the "balanced" set to ever have a decibel boost, between the bridge and neck pickup, that is much more than 3dB at the most, and in the case of humbucker sets, usually less. 


First, consider balanced Stratocaster sets, the "Fralin Vintage Hot" set has a "hot" bridge with a DC resistance of 6.8k, while the neck pickup has a DC resistance of only 6.0k. For that 800 added ohms of wire, the plot shows that the bridge only produces about 2dB of added output. On the other hand, the loaded peak drops from 4.2kHz way down to 3.6kHz, 600Hz of attenuation on the high end harmonics. So what's really happening here? The bridge is hardly any louder, but it is somewhat deal darker in tone.

Note that these plots have a vertical scale of 5dB per division.



This same trend follows for many different Strat tests I've tested. Here is a Lollar Tweed set, the bridge is 5.9k, the neck is 5.3k, and again, 600 ohms of difference doesn't amount to much more than a 2dB difference in loudness, but the resonant cut off differs by about 500Hz.





Now for P.A.F clones. This Seymour Duncan Jazz set had a bridge pickup that was wound to 8.2k ohms, and a neck wound to 7.5k, 700 ohms difference, and yet there is barely 1dB difference in output for a given input. On the other hand, the loaded peak frequency drops from 3.1kHz to 2.8kHz, slightly softening the treble response of the bridge pickup.

Note that these plots have a vertical scale of only 1dB per division.




The same can be seen for the Tonerider AC4 PAF clone set. 800 ohms of separation between neck and bridge, almost precisely 1dB difference in output, and a difference of 130Hz in harmonic treble content




The case of a Telecaster is a little difference because the neck and bridge pickups are actually different pickups. In testing, the neck pickup is usually about 5dB quieter, in part because it is wound lower, but also because the metal cover puts added distance between the coil, the pole pieces and the strings or test coil, relative to the bridge pickup.


In conclusion, in the balanced Strat pickups and typical PAF balanced sets, where the bridge is wound from 0.5k to 1k ohms hotter than the neck, the difference in volume output is only about 1dB to 2dB, differences that are only perceptible in "laboratory" conditions. Meanwhile, this extra wire shifts the peak frequency downwards by several hundred hertz, well beyond the perceivable minimum of human hearing. Therefore, the intention of a balanced set is not to volume match the neck and bridge, but rather to reduce the treble content of the bridge pickup, so that it will sound "fatter", "less shrill" etc. relative to the neck pickup.

The only true means of volume matching is to set the pickups at difference heights away from the strings, which dramatically alters the amount of magnetic interaction between the strings and pickup, and therefore the output voltage.


One caveat is that there are some sets out there where the bridge is so much hotter than the neck that both the amplitude and the frequency of the bridge are remarkably set apart from on another.

For example, TV Jones went a little nuts with their Magna'tron set:




The bridge has 3k more resistance and nearly three times the inductance of the neck, but even so, it appears that despite that extra volume of wire, only about a 3.5dB difference in output is realized.

There are sets on the market, especially from Seymour Duncan and DiMarzio, where the bridge is significantly hotter than the neck, such as the JB/Jazz, SSL-5/SSL-1, or the Super Distortion / PAF Pro pairings, however, more so called "balanced" sets generally feature a bridge pickup that is trivially over-wound compared to the neck and/or pickup.

[reTrEaD]

In general, the neck position is louder than the bridge, because the wider string movement over the neck pickup means there is more fundamental and lower harmonics amplitudes. So there are two "problems" with bridge pickup, they're too quiet and they're too bright. But I content that a "balanced" set really only addresses the fact that the bridge is too bright, and not that it's too quiet.

I believe that's a fair assessment. I reckon the pickup manufacturers would prefer to address the volume issue more effectively if they could. But you do what you can with what you have to work with.

'Balanced' seems a misnomer. But 'disparity partially mitigated' would be a rather clumsy, albeit more accurate, description.

[antigua]

Feb 7, 2018 0:09:04 GMT -5 reTrEaD said:

In general, the neck position is louder than the bridge, because the wider string movement over the neck pickup means there is more fundamental and lower harmonics amplitudes. So there are two "problems" with bridge pickup, they're too quiet and they're too bright. But I content that a "balanced" set really only addresses the fact that the bridge is too bright, and not that it's too quiet.

I believe that's a fair assessment. I reckon the pickup manufacturers would prefer to address the volume issue more effectively if they could. But you do what you can with what you have to work with.

'Balanced' seems a misnomer. But 'disparity partially mitigated' would be a rather clumsy, albeit more accurate, description.

AFAIK, if they simply used 44AWG or 45AWG, and used a very small bobbin that could be be set really close to the strings, then a larger number of the coil loops would see a larger magnetic delta from the guitar string, and therefore product more overall voltage. With a typical Fender bobbin, those coil turns near the base of the pickup are not seeing much of a magnetic shift, and so their major contribution is just to the inductance of the pickup. Take a look at a humbucker for example, it's like you split a Fender coil in half, and put each half close to the strings, and suddenly you're realizing a +5dB voltage output.

An interesting thing also is that the steel cores do a better job of conveying flux than do AlNiCo cores, so this height issue disproportionately effect Fender AlNiCo single coils, where as those stock ceramic single coils with the steel slugs are less effected by their bobbin height, and consequently they are a lot louder, almost 5dB  according to this test guitarnuts2.proboards.com/thread/7882/output-amplitudes-various-pickups?page=2

[newey]

Now for P.A.F clones. This Seymour Duncan Jazz set had a bridge pickup that was wound to 8.2k ohms, and a neck wound to 7.5k, 700 ohms difference, and yet there is barely 1dB difference in output for a given input. On the other hand, the loaded peak frequency drops from 3.1kHz to 2.8kHz, slightly softening the treble response of the bridge pickup.

With an LP/SG style guitar having individual 500K V and T pots, my seat-of-the-pants WAG is that a slight tweak of the bridge tone control, to about 8-9, would accomplish approximately the same frequency drop. A Bode plot might prove me wrong, but that's my suspicion.

If one uses a "treble bleed" circuit for the V pots, the volume differential could be resolved with a slight tweak downward on the neck volume.

Of course, guitar manufacturers know that most guitarists never touch their knobs . . .

[ms]

Feb 7, 2018 0:09:04 GMT -5 reTrEaD said:

In general, the neck position is louder than the bridge, because the wider string movement over the neck pickup means there is more fundamental and lower harmonics amplitudes. So there are two "problems" with bridge pickup, they're too quiet and they're too bright. But I content that a "balanced" set really only addresses the fact that the bridge is too bright, and not that it's too quiet.

I'd prefer to turn that around and say that because the neck pickup is located where it sees a greater amplitude of fundamental motion, the amplitude of string motion is greater.  The bridge pickup does not see the full motion of any of the lower harmonics, and so in a sequence of harmonic responses, the first several are all increasing with respect do the previous one.  The neck pickup sees plenty of higher harmonics and it can be quite bright.

[ms]

Feb 7, 2018 6:20:59 GMT -5 newey said:

Now for P.A.F clones. This Seymour Duncan Jazz set had a bridge pickup that was wound to 8.2k ohms, and a neck wound to 7.5k, 700 ohms difference, and yet there is barely 1dB difference in output for a given input. On the other hand, the loaded peak frequency drops from 3.1kHz to 2.8kHz, slightly softening the treble response of the bridge pickup.

With an LP/SG style guitar having individual 500K V and T pots, my seat-of-the-pants WAG is that a slight tweak of the bridge tone control, to about 8-9, would accomplish approximately the same frequency drop. A Bode plot might prove me wrong, but that's my suspicion.

If one uses a "treble bleed" circuit for the V pots, the volume differential could be resolved with a slight tweak downward on the neck volume.

Of course, guitar manufacturers know that most guitarists never touch their knobs . . .

IMO, damping the resonant peak (tone control) and lowering its frequency (increasing inductance and/or capacitance) are distinct audible effects, but maybe not if both effects are small.

[reTrEaD]

Feb 7, 2018 1:02:03 GMT -5 antigua said:

AFAIK, if they simply used 44AWG or 45AWG, and used a very small bobbin that could be be set really close to the strings, then a larger number of the coil loops would see a larger magnetic delta from the guitar string, and therefore product more overall voltage. With a typical Fender bobbin, those coil turns near the base of the pickup are not seeing much of a magnetic shift, and so their major contribution is just to the inductance of the pickup. Take a look at a humbucker for example, it's like you split a Fender coil in half, and put each half close to the strings, and suddenly you're realizing a +5dB voltage output.

So maybe they aren't doing the best they can with what they have to work with? I suppose one could say keeping the coil form factor a constant is not necessarily a good thing in this case.

Another thing that always bugged me is staggered pole pickups.  They require the coil to be farther away because the stagger means some poles stand proud. It would seem to make more sense to 'balance' the strings by recessing the poles for some strings rather than having any stand proud. Maybe there's something I'm overlooking? idk.

[reTrEaD]

Feb 7, 2018 10:33:48 GMT -5 ms said:

I'd prefer to turn that around and say that because the neck pickup is located where it sees a greater amplitude of fundamental motion, the amplitude of string motion is greater.  The bridge pickup does not see the full motion of any of the lower harmonics, and so in a sequence of harmonic responses, the first several are all increasing with respect do the previous one.

Turnabout is fair play when looking at this.

I'd like to take a slight tangent and look at a special case or 'sweet spot' so to speak. If we look at a case where the neck pickup would be located where the 24th fret should be and we fret a string on the 12th, the antinode for the fundamental and an antinode for all the odd harmonics falls directly above the neck pickup. And a node for all even harmonics exists there as well. But to my ear, this doesn't sound peculiar or abrupt compared with fretting at different locations where the odd harmonics begin to lose the advantage and the evens begin to become more present (except when flagging a second harmonic). It seems like the ear or brain is satisfied with the loss of even harmonics when the odd harmonics are present at greater levels.

The neck pickup sees plenty of higher harmonics and it can be quite bright.

Plenty seems a relative thing. The absolute output of those higher harmonics should indeed be considerable. But in relation to the level of fundamental and lower harmonics, it's rather modest.

In the case of a bridge pickup where the fundamental and lower harmonics are basically castrated, even a slightly lower absolute level of upper harmonics will seem disproportionately large.

[antigua]

Feb 7, 2018 13:15:44 GMT -5 reTrEaD said:

Feb 7, 2018 1:02:03 GMT -5 antigua said:

AFAIK, if they simply used 44AWG or 45AWG, and used a very small bobbin that could be be set really close to the strings, then a larger number of the coil loops would see a larger magnetic delta from the guitar string, and therefore product more overall voltage. With a typical Fender bobbin, those coil turns near the base of the pickup are not seeing much of a magnetic shift, and so their major contribution is just to the inductance of the pickup. Take a look at a humbucker for example, it's like you split a Fender coil in half, and put each half close to the strings, and suddenly you're realizing a +5dB voltage output.

So maybe they aren't doing the best they can with what they have to work with? I suppose one could say keeping the coil form factor a constant is not necessarily a good thing in this case.

I think when it comes to pushing amps harder, they found their answer in humbuckers. I don't think that making single coils push harder is even a priority for pickup makers, despite how they market their "hot" single coils, as the thesis says, it's really just about delivering a darker tone.

The real innovation, if it can be called that, seems to be going in the other direction; reduce noise levels instead of boosting the signal. In fact, a stacked humbucker design reduces the overall signal by about 3dB, but presumably reduces noise to a greater extent. I'm still curious to find out why stacked designs sound "bad". I wonder if reduce voltage output in an of itself sounds "bad".

[reTrEaD]

Feb 8, 2018 12:46:28 GMT -5 antigua said:

I think when it comes to pushing amps harder, they found their answer in humbuckers. I don't think that making single coils push harder is even a priority for pickup makers, despite how they market their "hot" single coils, as the thesis says, it's really just about delivering a darker tone.

I wasn't thinking so much about the shorter coil form as something to be used in all SCs. Just for the bridge, to mitigate the loss of fundamental, then tweak the response for something a bit more tonally pleasing. idk.

The real innovation, if it can be called that, seems to be going in the other direction; reduce noise levels instead of boosting the signal. In fact, a stacked humbucker design reduces the overall signal by about 3dB, but presumably reduces noise to a greater extent. I'm still curious to find out why stacked designs sound "bad". I wonder if reduce voltage output in an of itself sounds "bad".

Stacked designs are hum-canceling.  60 cycle hum is part of the vintage sound.  Vintage is always sounds better, right?  [/facetiousness]

Your A&R of the Fender VNs points to a couple of suspects.  Much lower Q factor, much higher unloaded resonant frequency.  When loaded, the peak falls into a more typical range but it's slightly less pronounced.  Also, the higher magnetic pull on the strings is probably not a good thing.  Likely to be much more to the story than that, though.

[ms]

Feb 8, 2018 12:46:28 GMT -5 antigua said:

I'm still curious to find out why stacked designs sound "bad". I wonder if reduce voltage output in an of itself sounds "bad".

I thought it was because the inductance and resistance rise because they are (usually, I think?) wound with more total turns using small wire, and thus lose highs.  But maybe there is more to it than that.  

[antigua]

Feb 9, 2018 13:49:52 GMT -5 ms said:

Feb 8, 2018 12:46:28 GMT -5 antigua said:

I'm still curious to find out why stacked designs sound "bad". I wonder if reduce voltage output in an of itself sounds "bad".

I thought it was because the inductance and resistance rise because they are (usually, I think?) wound with more total turns using small wire, and thus lose highs.  But maybe there is more to it than that.  

I analyzed a set www.strat-talk.com/threads/fender-vintage-noiseless-analysis-and-review.404990/ , I saw a drop in Q factor, relative to "true" Strat single coils, which at the time I remarked was significant but with more hindsight I doubt the Q factor was diminished enough to matter. Even if the Q was low, it could be fixed with 1 meg pots, though I've not tried it one way or the other. 

I think I have a theory:


Fender Noiseless Bridge

DC Resistance (series): 10.27K

top: 5.14K

bot: 5.18K

Inductance (series): 2.592 H

top: 1.445H

bot: 1.591H

Resonant Peak: 13.7kHz kHz

Calculated C: 32pF (52-20)

Coil width: top: 0.6090" bottom: 0.5870"


The wire gauge is likely 44AWG, to achieve only 2.6H with 10k DC R, so lets say there are 8000 turns total, 4000 turns of 44AWG per coil, that means the productive top coil only has 4000 turns of wire produces a series voltage, where as your typical Strat pickup has 8000 turns all producing some productive voltage. That means the overall level of the pickup should be quite a bit lower than a typical Strat pickup, notwithstanding whether the coil is split or not. I can test this later by comparing the Noiseless voltage to a typica Strat pickup with ~2.6H inductance.

[Deleted]

Antigua, why don't you start your own pups brand? Design the custom pups by order, then give the specs to some asian maker and deliver the final product to the customer. I think you would be very very successful. Heck, I'd love to be your customer!

[antigua]

Feb 10, 2018 8:35:30 GMT -5 @pyrros said:

Antigua, why don't you start your own pups brand? Design the custom pups by order, then give the specs to some asian maker and deliver the final product to the customer. I think you would be very very successful. Heck, I'd love to be your customer!

Thanks for the vote of confidence. I think companies like Tonerider and BYO are doing exactly what I would do myself, and as Chinese companies like Donlis get better at consistently turning out quality pickups, there's going to be less of a reason for Americans to intervene in the business. 

If it were up to me, I'd market pickups as electrical components, and try to relate performance in fact based terms, but the market these days is based around word of mouth recommendations, endorsement deals and creative marketing that often bends the truth. If you don't operate on those terms, you would probably lose all your business to those operators who do. The salesmen win out over the science nerds. I'd rather just recommend BYO and Tonerider and call it good. I think trying, and I stress "trying", to share good information is the best use of my time.

[blademaster2]

Antigua,

As a (fellow?) electrical engineer I appreciate your efforts and solid approach to obtaining good, controlled results, especially in comparing the electrical characteristics of various pickups. These are really good, to me, as a basis for understanding any differences that I hear and appreciate when I try different pickups and circuits.

I do have a question, however, based on my recent "testing" to hear the (very, very slight) difference that a metal cover made in the tone of my neck-position SSL-1. I am convinced that I hear a difference with/without the cover in place, and that it is nonetheless very subtle - a slight loss of high frequency response. This cover, from StewMac, is not attracted to the pickup magnets and therefore I accept that this difference is due to eddy currents (perhaps also its capacitance to the coil wire, although the cover was not grounded in my tests as I needed to be able to slip it in and out of place so any effect from the capacitance would be distributed to and from the coils to complete any "bleed path").

If I understand your testing technique, you excite the pickup using a coil (with no core magnets, I gather) placed over the pickup under test and feeding your sweeped sinewave excitation signal into it so you can measure the output frequency amplitude generated by the pickup under test - with and without cable loading.

If the electrically-conductive metal of the cover influences the response, won't you alter the pickup response in your test set up due to the presence of the excitation coil, having so much more metal than the cover has? That would introduce an experimental error into all of your results, albeit equally for all of the pups you test and therefore not invalidate the results for comparative purposes.

If this is making any difference, then the optimum test configuration would really be a piece of stainless steel (same as a guitar string) placed over the pickup and caused to move in a motion that is a sinusoidal sweep through the frequencies of interest (by a motion control system mechanical coupling that is neither magnetically permeable nor electrically conductive), causing the pickup to respond exactly as it would with a vibrating guitar string near it.

I would be very interested to hear if that, or something equivalent, has ever been attempted.

[JohnH]

I thought Id put up something from GuitarFreak to illustrate the issue of balanced or unbalanced pickups.

The issue of exactly what is the relative signal level between two pickups is one of the hardest to nail in a test or analysis, but it is easier to show the relative results of two identical pickups. These plots assume a CS69 based on Antigua's testing, in Strat neck and bridge positions. They are at the same (but undefined) height, strings fretted at 3rd. strummed 110mm from the bridge.

Two types of plot are shown here: The spiky ones show each individual harmonic, while te smoother ones are an envelope, assuming some other notes may be played around that fret position too.

So according to all th theory implied by this calc, there is up to about 8db of difference through the midrange, and obviously the bridge is a bit brighter at high frequency relatively. It is not obvious what volume change would be needed to bring a audible/musical balance, also noting that some of this can be achived by pickup height adjustment.

Attachments:

[ms]

Feb 11, 2018 14:21:53 GMT -5 blademaster2 said:

Antigua,

As a (fellow?) electrical engineer I appreciate your efforts and solid approach to obtaining good, controlled results, especially in comparing the electrical characteristics of various pickups. These are really good, to me, as a basis for understanding any differences that I hear and appreciate when I try different pickups and circuits.

I do have a question, however, based on my recent "testing" to hear the (very, very slight) difference that a metal cover made in the tone of my neck-position SSL-1. I am convinced that I hear a difference with/without the cover in place, and that it is nonetheless very subtle - a slight loss of high frequency response. This cover, from StewMac, is not attracted to the pickup magnets and therefore I accept that this difference is due to eddy currents (perhaps also its capacitance to the coil wire, although the cover was not grounded in my tests as I needed to be able to slip it in and out of place so any effect from the capacitance would be distributed to and from the coils to complete any "bleed path").

If I understand your testing technique, you excite the pickup using a coil (with no core magnets, I gather) placed over the pickup under test and feeding your sweeped sinewave excitation signal into it so you can measure the output frequency amplitude generated by the pickup under test - with and without cable loading.

If the electrically-conductive metal of the cover influences the response, won't you alter the pickup response in your test set up due to the presence of the excitation coil, having so much more metal than the cover has? That would introduce an experimental error into all of your results, albeit equally for all of the pups you test and therefore not invalidate the results for comparative purposes.

If this is making any difference, then the optimum test configuration would really be a piece of stainless steel (same as a guitar string) placed over the pickup and caused to move in a motion that is a sinusoidal sweep through the frequencies of interest (by a motion control system mechanical coupling that is neither magnetically permeable nor electrically conductive), causing the pickup to respond exactly as it would with a vibrating guitar string near it.

I would be very interested to hear if that, or something equivalent, has ever been attempted.

You can drive the coil with a current source (high impedance). Since it is effectively open, then you cannot induce much, if any significant, current in it.  I have used coils as small as about 3/16 inches in diameter with just three turns, driven from a power amp with about 1 amp, with an 8 ohm resistor in series.  Results do not change much if you make the coil bigger, and so I think that the measurements are not much compromised.  But I have not made any real measurements to quantify the interaction.  I believe that KW has in his paper that is referenced somewhere around here.

[antigua]

Feb 11, 2018 14:21:53 GMT -5 blademaster2 said:

If I understand your testing technique, you excite the pickup using a coil (with no core magnets, I gather) placed over the pickup under test and feeding your sweeped sinewave excitation signal into it so you can measure the output frequency amplitude generated by the pickup under test - with and without cable loading.

If the electrically-conductive metal of the cover influences the response, won't you alter the pickup response in your test set up due to the presence of the excitation coil, having so much more metal than the cover has? That would introduce an experimental error into all of your results, albeit equally for all of the pups you test and therefore not invalidate the results for comparative purposes.

If this is making any difference, then the optimum test configuration would really be a piece of stainless steel (same as a guitar string) placed over the pickup and caused to move in a motion that is a sinusoidal sweep through the frequencies of interest (by a motion control system mechanical coupling that is neither magnetically permeable nor electrically conductive), causing the pickup to respond exactly as it would with a vibrating guitar string near it.

I would be very interested to hear if that, or something equivalent, has ever been attempted.

The excitation coil is extremely small. I posted details about it is another thread, which I can't find now, but heres a pic:



I've used a variety of exciter coils and I've always got the same response curves, even when the exciter coil was as larger as another guitar pickup, showing that almost without exception, the magnetic coupling between the exciter and the pickup is very tiny.

This exciter I use now is a 2mm tall coil that is about 100 turns of 44 AWG, wrapped around a slimmed down Popsicle stick. The geometry is intended to be similar to a guitar string in order to measure eddy current effects as close to in situ as possible. 

[antigua]

(FYI I'm cross posting this to the Fender Noiseless analysis also)

Regarding the output of a stacked humbucker, I just did a side by side test between a Seymour Duncan SSL-1 and a Fender Noiseless. Both pickups have an identical inductance of 2.6H. The SSL-1 has a DC resistance of about 6.5k and the Noiseless about 10k. 

Here's the result:



Using the Noiseless as the baseline, for a given input excitation of 4Vpp with the exciter coil, the SSL-1 produced  +2.8dBV, and the top coil by itself produces +2.4dBV. So the humbucking mode definitely causes a small  output drop, but it appears that using the top coil alone produces just about as much voltage as the SSL-1.

Now for the resonance differences:



When in series, the higher series resistance and maybe some mutual inductance between the top and bottom coils of the Noiseless cause a lower +5.0dB boost at resonance, where as both the top coil by itself and the SSL-1 produce +7.0dB at resonance.  Of course, the inductance of the top coil by itself is only about 1.5H, so the loaded resonant peak is 5.67kHz, quite a bit higher than a typical Strat pickup, and likely to sound very bright. 

The Fender Noiseless' 2.8dB drop in output voltage compared to the SSL-1 is not very much, and if the small difference in resonant Q factor is audible, that could be compensated for by using a 500k ohm tone or volume pot.