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Tech: Setup, Repairs and Mods Guitar workbench discussion such as setup, repairs, mods, installing new parts and more.

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  #1  
Old 08-26-2001, 01:59 PM
puppiesonacid  is offline
 
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1 meg volume pot - what do they do?


ive heard that 1 meg volume pots help to maximize the output, flexibility and tone of high gain pickups, just wondering if its true.

thanks

God bless

Tony
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  #2  
Old 08-26-2001, 03:08 PM
SalemB  is offline
 
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1 meg volume pot


No, that can't be true. When your Volume is at 10, the pot *is shorted and the signal runs straight through.

The electronics of guitars is passive circuits (no batteries included). This means that you can only damp the signal or filter the frequencies.

To maximize output, connect the pickup wire directly to the output (it should be the same as turning the volume pot to 10).
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  #3  
Old 08-27-2001, 12:21 AM
shawn  is offline
 
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1 meg volume pot


i have to disagree, i have used 1 meg tone and volume pots together and separately and there is a huge HUGE difference. *

you used 250k on a strat with single coils -- why? *to dampen the shrill highs. *you use 500k with humbuckers -- why? *because they are warmer and darker and would sound more muffled with a 250k. *same principle, use the 1 meg pot and it gives less resistance to the signal letting more overall signal through, but since the first thing to go is the higher frequencies, they are also the first to return. *even a 1 meg pot on 10 is not as little resistance as no pot at all and is certainly less resistance and more bright than a 500k on 10. *

but be forwarned, if you put 1 meg pots in the tone and volume of your guitar it will sound like a fully open wah pedal. *

i have a paf7 and an evo7 in my UV and they were originally too muddy and lacked the harmonic response that i like --- after trying many configurations, im now with a 500k in the volume and a 1 meg in the tone with a .33 microfarad cap on the tone instead of the .22 -- this helps to make the tone control more effective against such an abundance of high frequencies. *the 500k on the volume helps to add the warmth back in after opening up the floodgates on the tone control. *very high output though. *

try it, its not like you cant put it back to stock if you dont like it.
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  #4  
Old 08-27-2001, 05:22 AM
rickboot  is offline
 
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1 meg volume pot


SalemB

You are partially right. The signal flows is shorted through the pot. However, when the volume and tone controls are maxed, the signals are being kept above ground by the max resistance (e.g. 500K) of the pots. This resistance to ground affects the tone probably due the LC and RC networks formed by the pickups and tone circuits. The general result is that higher the resistance pots make for a brighter sound.

Rick
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  #5  
Old 08-27-2001, 08:33 AM
SalemB  is offline
 
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1 meg volume pot


Yes, you're right, Rick.
I made a small drawing based on the wiring diagram.



The value of the pot controls the output impedance. To maximize output this should be matched with the input impedance of the amp. I checked the manual for my Behringer and it says 1 Mohm. It is therefore likely that you get a better match with a 1 M ohm volume pot.

Someone might be able to do the math here. I'm not
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  #6  
Old 08-27-2001, 02:53 PM
RSVampire  is offline
 
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1 meg volume pot


all a volume pot is doing is adding resistance to the output to dampen or kill the sound. If you use a 1Mohm pot you only have to turn it half-way down to kill the sound instead of all the way down on a 500k since a 1Mohm pot is twice as much resistance. Oh and that thing about using the 250k on singles and 500k on humbuckers is totally wrong. You use 250k because singles are a lot less output then humbuckers....500k is need to kill the sound at 0. I love knowing electronic stuff
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  #7  
Old 08-27-2001, 03:35 PM
ripl3y  is offline
 
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1 meg volume pot


Quote:
Quote: from shawn on 12:21 am on Aug. 27, 2001
you used 250k on a strat with single coils -- why? *to dampen the shrill highs. *you use 500k with humbuckers -- why? *because they are warmer and darker and would sound more muffled with a 250k.
The capacitors control/deal with the amount of treble or bass, not the pots.
The higher capacitor value, the more treble is cut out and vice/versa.

Steve
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  #8  
Old 08-27-2001, 03:35 PM
shawn  is offline
 
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1 meg volume pot


i think you have it backwards man, *the 1 meg has less resistance therefore letting more sound through, which is why its brighter. *and if you turn a 1 meg pot half way down, it is still brighter and has more output than a 500k at full volume ----- i know this because i play both every day. *i dont know the exact electrical principles that make these things happen, i just know how they react cuz ive experimented with them a lot.
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  #9  
Old 08-27-2001, 03:42 PM
ripl3y  is offline
 
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1 meg volume pot


Judging by the time we both posted, I take it you mean rsvampire not me.

Personally, I gave up trying to work pots out ages ago, I'll just go with what the big guys use

Steve

P.S. My capacitor statement still stands though.
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  #10  
Old 08-27-2001, 06:06 PM
SalemB  is offline
 
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1 meg volume pot


What rsvampire said is what I said initially. I'm not too sure anymore.

The tricky thing is that as soon as you connect the guitar to an amp your electronics will have to interface with the preamp. The circuit is therefore much dependant upon what amp your are using.
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  #11  
Old 08-27-2001, 09:12 PM
RSVampire  is offline
 
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1 meg volume pot


I agree with SalemB. And shawn you are not entierlly correct. The higher the impedance number the more resistance the pot can induce on whatever it going through it. usually highs/lows aren't affected by how much the pot vaule is (except on tone knobs) the pot's don't "allow" more or less sound to travel through them at all......if a humbucker only needs 500k to kill the sound, then there is no point in getting a 1Mega ohm pot because at half-way down it'll kill the sound. The only thing I can think of that made your sound brighter is better components within the pot itself...
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  #12  
Old 08-28-2001, 04:58 AM
toshiro  is offline
 
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1 meg volume pot


heh.

I agree completely with shawn. Having two guitars, both with 1 meg vol pots (no tone) , I can say for sure that it does not cut off at 5, but at 0 just like any other pot. They are slightly brighter than 500k's and massively brighter than 250k's..

I'm not gonna re-hash the single coil/humbucker thing because, again, shawn is right on that one.

Telecasters have used 1 meg pots in the past, to get extra brightness (if you ask me, they're bright enough with the 250k's )..

The resitance isn't pushing the signal to ground, it's pushing it away from ground. *So, when you roll the volume down, it's taking the resitance away, and letting the signal short out. When you turn it up, it puts whatever resitance in between the signal and ground.. Higher the pot's resitance, the more signal makes it out to the jack.. High feq.s bleed off more, so when you add more resitance, like stepping up to a 1 meg pot, we hear it as brighter.. *This is my theory, though I probably heard it somewhere before..
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  #13  
Old 08-28-2001, 05:52 AM
rickboot  is offline
 
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1 meg volume pot


Hmm. It seems a lot of people "think" they know what they are talking about.

rsvampire and shawn are wrong (anyone Devry grads here? ). Salemb has seen the light. That rickboot guy seems to know what he is talking about. Must have been that Navy training.

My first post was originally longer but I simplified it. I wished I hadn't now. Let me clarify and correct a few things:

1) 1 meg is twice as much as 500K, so a 1 meg pot has more resistance not less.

2) When the volume pot is turned to 0, the pot is shorting the signal to ground. Since the "signal" is grounded there is no sound. In affect there is no signal. The signal is one dead parrot. When it is above 0 the the pot is adding resistance between the signal and ground which means the signal can start doing it's thing.
Of course turning to 10 will add the max resistance of the pot (i.e. 500K) and the signal will be at it's highest. Turning to 11 will make you Nigel Tufnel.

3) The effect of having more resistance between the signal and ground DOES affect the tone. See my previous post.

4) The tone pot and cap work a little differently. Caps pass AC like guitar signals. Caps pass high freqs easier and impede (add resistance to) lower freqs more. The tone cap in the tone circuit pass is there to roll of the higher frequencies by sending them to ground. The tone pot adds more resistance between the tone cap and ground. When on 0 the pot adds no resistance so the cap can pass frequencies to ground more easily. When the pot is on 10, more resistance is added between which lets less frequencies, high or low, pass to ground. This is a gross simplification. There is some RC filter magic going on but I don't think we want to go there.

Rick
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  #14  
Old 08-28-2001, 09:54 AM
ed5150  is offline
 
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1 meg volume pot


Ha! That seems to have shut you other guys up!
Listen to what the man says, he knows what he's talking about. If you want full brightness and volume out of a guitar, I can also recommend having a switch put in the circuit to totally bypass the controls. I have this from the bridge pickup on my main guitar and it's fantastic. If anyone wants a little schematic, feel free to mail me.
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  #15  
Old 08-28-2001, 04:40 PM
keith  is offline
 
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1 meg volume pot


OH.

(Edited by keith at 10:45 pm on Aug. 28, 2001)
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Tags
bridge pickup, meg pot, nigel tufnel, volume pots, wah pedal, wiring diagram


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