Why 1 meg pots?

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909one
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Re: Why 1 meg pots?

Post by 909one » Mon Jun 11, 2012 11:08 am

I have my Jazzmaster wired like Gibson, the main bottom tone and vol controls are for the bridge pickup only. The old rhythm circuit is for the neck pickup. The remaining switch on the rhythm circuit I use to bypass the tone and volume control all together on the neck pickup. I have 250k pots on the Bridge Vol and Tone, 500k on the neck. I find that for the bridge pickup, having 1M pots is waaaay too bright for me. The difference between 1M and 250k is like putting a low-pass filter at around 5 or 6k. IMO, that frequency range in guitars is just where the annoying ice-pick happens and there is really no reason to hear that stuff... especially on the bridge pickup. The shimmer and chime still comes a lot from the 1k-4k range, and by having a 250k pot in there its perfect amount of treble for me. I like bright guitars, a lot. But I feel like there is no reason for 1M pots. Like I mentioned above, I wired the extra switch to bypass the volume and tone in neck position, thinking it would be nice to make the neck a little less muddy when needed, but honestly in a band situation it almost does nothing to make you cut through anymore in the mix. It just makes the tone more scooped, which actually makes things cut through less. Its all about selective upper-mids.

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Re: Why 1 meg pots?

Post by jorri » Mon Jun 11, 2012 3:20 pm

IMO with the tone turned down coupled with 1meg volume you don't get a complete loss of any attack or clarity like you do with 250ks. I get better, non muddy dark tones. And i get icepickiness which i like, coming from listening to a lot of post-punk. volume full, tone on 7 with 1megs sounds better than 250ks on full, although its about the same tonal range. If i want the rounder sound my amp also has a treble know, and even being an ac30 with a not so powerful EQ it can take it well below what changing the pots would do. best to leave it open and EQ later if you want to go back to mud.

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Re: Why 1 meg pots?

Post by Libtoem » Tue Jun 12, 2012 3:16 am

Never been to much of fan for I meg pots,I have jag wired for just two individual volumes,bridge has 250k and neck has 500k and a kill switch but my Xaviere jazzmaster copy is wired like my jag but I have humbuckers so I have 500k in the bridge and 1meg in the neck.

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Re: Why 1 meg pots?

Post by Sinuata » Tue Jun 12, 2012 11:16 am

Image

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Re: Why 1 meg pots?

Post by QuercusKirkus » Wed Jun 13, 2012 1:01 am

Hi all,
You might like this : http://sound.westhost.com/pots.htm" onclick="window.open(this.href);return false;

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Jefflee
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Re: Why 1 meg pots?

Post by Jefflee » Wed Jun 13, 2012 5:24 am

I don't have too much to add to this discussion other than this:- I have a L-series Jaguar and a CIJ Jazzmaster and I DON'T use the rhythm circuit on either because it dulls off the tone way too much. The CIJ Jazzmaster is way too bright - I'm looking at replacement pickups (opinions invited) as we speak. I converted the rhythm circuit switch on my CIJ Jazzmaster to be a volume and tone bypass and I really can't tell the difference between bypass, and non-bypass, so 1meg pots on full are basically invisable! I REALLY believe the pickups are way more important than the pots. My old Jag sounds awesome and I very rarely wind down the tone. ;)

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Re: Why 1 meg pots?

Post by cyclopean » Sun Jun 30, 2019 11:12 am

Hoops wrote:
Thu Jun 07, 2012 12:33 am
fisonic wrote:More so, why a 50k tone pot in the rythm circuit?
To keep things Jazzy 8)
but you can just turn down a higher knob. the rhythm circuit is close to unusable.

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Re: Why 1 meg pots?

Post by JVG » Sun Jun 30, 2019 12:36 pm

cyclopean wrote:
Sun Jun 30, 2019 11:12 am
Hoops wrote:
Thu Jun 07, 2012 12:33 am
fisonic wrote:More so, why a 50k tone pot in the rythm circuit?
To keep things Jazzy 8)
but you can just turn down a higher knob. the rhythm circuit is close to unusable.
That’s what I thought until I “discovered” using the rhythm circuit through a Rangemaster style treble booster or Tone Bender style fuzz. That’s when some really cool stuff starts happening with the rhythm sound!

J.

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Re: Why 1 meg pots?

Post by Danley » Sun Jun 30, 2019 1:18 pm

The rhythm circuit still has a 1 meg pot; it isn’t *that* muddy really.
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Re: Why 1 meg pots?

Post by 601210 » Mon Jul 01, 2019 5:22 am

I remember reading here that someone measured it out, and the 1 meg pot and usual capacitor make a resonant peak that's part of the jazzmaster quirkiness. Rolling the volume down just a touch gets rid of it without losing volume. I don't really like treble bleeds, for that reason among others.

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Re: Why 1 meg pots?

Post by soggy mittens » Mon Jul 01, 2019 6:51 am

1meg ftw, but this is one offset guitarist that I dig that has a dark tone....

https://www.youtube.com/watch?v=G1iYiMaf8R8
If OSG has tort me anything...

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Re: Why 1 meg pots?

Post by jorri » Wed Jul 03, 2019 8:03 am

To me, its like 'default tone' is on half. which kind of makes sense: if you borrow a muddy amp at least you aren't stuck. In theory I reckon that is about the same as 250k, but not exactly as there is a capacitor involved. Sometimes i get an over-bright amp I can either turn the tone down to about half, or even turn the volume to 9-i have no treble bleed. To me either way actually ends up 'darker' than 250ks, but then again you might not like the sound of the tone or volume being turned down-having things on full is perhaps more natural?

In practice, i just grow to like it and usually leave it on full. Its a resonant peak around where the guitar's attack is (pretty useful for twang and sounding like a spagetti western), whereas a 250k setup is about 'flat'. Its basically that a 250k setup corrects this peak that occurs from the pickup, but 1megs lets most through unfiltered rather than 'create' that peak. Even moreso for a strat, or jazz bass, at least on the 'inbetween' settings, the resistance is in parallel so a strat has 250/3=83.3...whereas jazzmaster would always have 1000/2=500.

In fact I just cut the tone control out my jazz bass- i intend to replace with 500/500/1meg eventually because tone control does get used a bit, it was just off the cuff before recording where i lacked attack.. 83 is way low! so now i guess in the middle position its 125, or 250 with a single pickup... I have an amp EQ but it only really takes things away, not puts back what's not there in terms of attack.

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Re: Why 1 meg pots?

Post by oid » Sat Jul 06, 2019 12:34 pm

The 1Meg pots in the lead circuit are there for exactly as previously stated, brightness, the higher value pots loads down the pickups less so more high frequency gets through. The simple explanation is that resistance (impedance) is not constant over frequency, that 1Meg is 1Meg at DC, frequency of zero, when we feed it an AC signal like the output of a guitar pickup we get a different resistance for our E2 6th string than our E4 1st, so we get different amplitudes for different frequencies. Despite popular belief, turning your volume down does not make it mimic a lower value pot, if you measure the resistance between the outer two lugs of a pot you will see that the resistance is always the same regardless of the knobs rotation and this is the value the pickup sees, a parallel resistance of constant value to ground. There is some effect caused by the fact that the output of the guitar sees two varying resistance, one in series with the pickup and one to ground, but this again has no relation to a lower value pot, it does have more effect on the sound than the other end, but it still is not mimicking the lower value pot, the overall resistance remains constant. That is purely academic anyways, all that matters is that we loose some high end as we turn down the volume and larger value volume pot will give us more highs assuming everything else stays the same.

The 50k pot in the rhythm circuit is because it is not your standard tone control. Most guitar tone controls sweep the cutoff frequency of the filter, so with the tone rolled back all the way the filters cutoff may be 100hz, all the way up the cutoff is essentially infinity and we can sweep that frequency anywhere between those two extremes, it is a variable frequency lowpass filter, the amount of cutoff is constant but the frequency at which the cutoff happens is variable. In the rhythm circuit that filter is fixed in frequency at about 160hz (E3) for the JazzMaster and 320hz (E4) for the Jaguar, as we roll back the tone we vary the amount we cut the frequencies above that cutoff point, it is a fixed frequency lowpass filter, the amount of cutoff is variable but it always happens at the same frequency. So if you change the value of the 50k pot you change the cutoff frequency of the filter, we can easily calculate new values with:

F=1/(2piRC)
F in Hertz
R in megaOhms
C in microFarads

Here are the plots of the classic JazzMaster circuit, top is lead, bottom rhythm.
Image
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Re: Why 1 meg pots?

Post by jorri » Sat Jul 06, 2019 1:01 pm

In actual outcome, because its not a simple RC, you have pickups with inductance and resistance it looks more like this:

Image

whilst the standard tone pot is more like this:

Image

which is that, first it rolls off the resonant peak, then when very low it creats another resonant peak where the RC cutoff frequency is.

Except, the rhythm circuit is not wired that way, so the cutoff doesn't vary and a resonant peak isn't created: hence why the volume drops a lot more when rolled down, its also acting like a potential divider/volume pot. It will also contribute to the overall impedance as in the first graph, meaning the pickups will see more lik 45k (or whatever is parallel 50k/1meg). A jaguar is also not wired the standard way: more like the rhythm circuit except includes an extra resistor to probably help volume dropping.

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Re: Why 1 meg pots?

Post by oid » Sat Jul 06, 2019 1:39 pm

My plot is to show the difference between the filter responses, not the frequency response of the entire system. The plots you posted look to be the plotting the effects the circuit has on pickups own response, they do not in anyway reflect the actual output of the guitar, the guitars tone circuits can and will completely remove those resonant peaks, they are only there as shown when the tone and volume are at max and other than the no-load plots do not say what the load is they are driving which also affect that resonant peak.

There is a resonant peak on the rhythm circuit as well but it only shows itself when the tone control is fully open. The volume drop of the rhythm circuit is only above the cutoff of the filter, this has an effect on the volume of the notes below the cutoff since those notes have harmonics which are above the cutoff point. The volume drop is simply because you are filtering out signal, there is no drop if the tone is full open.

The Jaguar's extra resistor is part of the strangle switch, it is the R in the RC circuit along with one side of the tone pot, they are parallel, if memory serves correctly it is completely out of circuit when the strangle is engaged and has no effect.

You seem to be confusing the pickups response with overall response and the filters response, they are all separate things.
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