advice on volume pot/ pickup problem

[metalj]

can a volume pot be too hot? or is it the pickups ? or combined ???

my problem has surfaced since i bought a new all tube amp. my duncan pickups worked great as they are with my solid state amp, now with my tube amp, they are way too hot, they are distorting my distortion, if that makes sense.

I tried lowering the pickups, and turning my volume knob down, but nothing seems to work. The weird thing is i all my guitars have the same pickups in them, but my number one guitar is the one distorting on me. Im thinking that it has a 1k pot volume knob on it and my others have a 500k pot on them, so would that be the problem seeing that my other guitars sound fine with the same pickups???

Im just wondering how much a difference the volume pot would make, and if that a 1k pot would do that??

oh yeah and does lowering the pickup height, and or turning down my volume knob on a 1k pot the same as just putting in a 500k pot and still preserve tone??

hope i gave enough info for you.

thank you for your help.

[Light]

It shouldn't be the pot. The big question is how does it sound clean, because it could be a problem with the pickup.

Even if it does have a 1meg pot (I assume that is what you meant), that should just make it a bit brighter than a 500K pot.

Test it (and your other guitars) clean. Distortion just masks too much to make an informed evaluation of potential problems.

Without seeing it and hearing the issue, there is just no way I can tell you what the problem is, however.

One other possibility; test the resistance of the pickups. If you have others which are working well, then compare them to the one which is not. If there is a difference, you may have a pickup problem. Or else just replace the pot, and see if it makes a difference. I said it shouldn't be the pot, but I could be wrong, and pots are cheep.


Light

"Cowards can never be moral."
M.K. Gandhi

[ggunn]

If the volume is turned all the way up, the pot is out of the circuit except for the bleed to its grounded side, which should be minimal. Actually, with a smaller pot, more of the signal is lost, which is why most guitar manufacturers use a pretty large one. A bigger pot gives more signal at full on, not less.

The size of the pot is probably unrelated to your problem. Is there active circuitry in your guitar, i.e., does it use a battery? When the battery in an active guitar goes out, it distorts before it stops working. Does the guitar distort on other tube amps, or just yours? It could be a prob with the amp.

[metalj]

Originally Posted by ggunn

If the volume is turned all the way up, the pot is out of the circuit except for the bleed to its grounded side, which should be minimal. Actually, with a smaller pot, more of the signal is lost, which is why most guitar manufacturers use a pretty large one. A bigger pot gives more signal at full on, not less.

The size of the pot is probably unrelated to your problem. Is there active circuitry in your guitar, i.e., does it use a battery? When the battery in an active guitar goes out, it distorts before it stops working. Does the guitar distort on other tube amps, or just yours? It could be a prob with the amp.

nothing active, no battery. the amp is brand new, and sounds amazing with everyother guitar i own, so it must just be the wiring on the pickups, combined with the guitar?

I just wonder if the pickups can be wired differentely so they are a little brighter sounding, and less gain, or if ill need to but new pickups/guitar.

thanks for helping

[Middleman]

I would say its the pot. As mention before the 1k pots are passing a lot of highs. I used these for years with solid state amps but when I went back to a tube amp, I went back to 250 and 500 pots on my guitars.

I got tired of the super treble thing.

[ggunn]

Originally Posted by Middleman

I would say its the pot. As mention before the 1k pots are passing a lot of highs. I used these for years with solid state amps but when I went back to a tube amp, I went back to 250 and 500 pots on my guitars.

I got tired of the super treble thing.

Can you explain to me how a volume pot affects tone? A pot is a simple resistance configured as a voltage divider network, not a reactive circuit element.

A volume pot is not needed at all if you keep it turned up all the way (like a lot of guitarists do), and when it's up all the way, it doesn't matter what the value is because it's not even in the circuit any more*, since the wiper is shorted to the hot side of the pot.

*except for a tiny amount of signal bleed to ground through the pot resistor. A lower value pot loses more signal to this effect, not less.

[boingoman]

Originally Posted by ggunn

Can you explain to me how a volume pot affects tone? A pot is a simple resistance configured as a voltage divider network, not a reactive circuit element.

A volume pot is not needed at all if you keep it turned up all the way (like a lot of guitarists do), and when it's up all the way, it doesn't matter what the value is because it's not even in the circuit any more*, since the wiper is shorted to the hot side of the pot.

*except for a tiny amount of signal bleed to ground through the pot resistor. A lower value pot loses more signal to this effect, not less.

Actually, I think the pot is still in the circuit, as the wiper is still in contact with the carbon track.

As far as volume affecting tone, it happens not from the volume pot, but the tone control and associated cap(s). For sure if you back the volume off an a strat, you can get treble loss. But only because the tone pot and cap are still in the circuit.

I have seen (and done) a tone pot mod, opening it up and scraping the carbon off the track at the full up position, so the pot and cap are totally out of the circuit when the tone control is full up. No more treble loss when rolling off the volume.

Some Fender guitars have had this or a similar mod stock from the factory, where the goal is to bypass the tone circuit.

[Middleman]

It's also a resistor. Higher values pass more highs and can affect overall tone. How it is wired can also affect the tone.

[boingoman]

Originally Posted by Middleman

It's also a resistor. Higher values pass more highs and can affect overall tone. How it is wired can also affect the tone.

I would bet that the different value pot loads the signal from the pickup differently, rather than actually acting as a filter.

[ggunn]

Originally Posted by Middleman

It's also a resistor. Higher values pass more highs and can affect overall tone. How it is wired can also affect the tone.

Pardon me for saying so, but I don't believe you know what you are talking about. Resistance is non-reactive impedance and does not affect AC bandwidth, i.e. it neither blocks nor passes high frequencies. Look it up.

[Middleman]

Pardon me for saying, guitar electronics are not AC, they are DC. Look it up. Now they end up in an AC environment which is the amp but prior to that. Nope.

[ggunn]

Originally Posted by boingoman

Actually, I think the pot is still in the circuit, as the wiper is still in contact with the carbon track.

I can see that; the wiper is not quite a dead short to the hot pin because it is still on the track (although some pots have a metal contact on the end of the track that the wiper rides up on which makes a dead short). But still, the volume pot is *virtually* out of the circuit, as the resistance between the wiper and the hot pin is very small compared to the value of the pot and the impedances elsewhere in the circuit.

But still, this discussion has drifted a bit from the original question, which was if changing a volume pot to a much higher value would significantly reduce the signal level to the amp. It seems to me that in the case of the volume control being all the way up, such a small part of the resistance of the pot is in the signal path that the difference would be negligible.

Now, there is a signal loss path to ground though the pot disregarding the wiper, i.e. the other half of the voltage divider network. It seems to me, though, that a higher value pot would lose less signal that way when all the way up and deliver *more* signal to the amp, rather than the other way round. What do you think?

[Middleman]

I think you should go buy a 500k pot, solder it in place and see if that makes a difference.

Taking advice from the experts here could be dangerous.

By the way. Here is some useful information about pots:

Standard Variable Resistor

Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermet (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available.
Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment.

Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm.

The resistance and type of track are marked on the body:
4K7 LIN means 4.7 k linear track.
1M LOG means 1 M logarithmic track.

[acorec]

Not meaning to get into the conversation too far, Here is my comment:

Either 250K or 500K pots can be used with any passive pickups however the pot values will affect tone slightly. The rule is: Using higher value pots (500K) will give the guitar a brighter sound and lower value pots (250K) will give the guitar a slightly warmer sound. This is because higher value pots put less of a load on the pickups which prevents treble frequencies from "bleeding" to ground through the pot and being lost. For this reason, guitars with humbuckers like Les Pauls use 500K pots to retain more highs for a slightly brighter tone and guitars with single coils like Stratocasters and Telecasters use 250K pots to add some warmth by slightly reducing the highs. You can also fine tune the sound by changing the pot values regardless of what pot value the guitar originally had.

[ggunn]

Originally Posted by Middleman

Pardon me for saying, guitar electronics are not AC, they are DC. Look it up. Now they end up in an AC environment which is the amp but prior to that. Nope.

Now I KNOW you don't know what you are talking about... ;^)

[Middleman]

ggun, find one piece of information that indicates that guitar electronics are AC, alternatiing current and I will apologize. This I gotta see.

Acorec, thank you for your explanation, that is exactly what I was indicating but did not explain out as eloquent as you.

[ggunn]

Originally Posted by acorec

Not meaning to get into the conversation too far, Here is my comment:

Either 250K or 500K pots can be used with any passive pickups however the pot values will affect tone slightly. The rule is: Using higher value pots (500K) will give the guitar a brighter sound and lower value pots (250K) will give the guitar a slightly warmer sound. This is because higher value pots put less of a load on the pickups which prevents treble frequencies from "bleeding" to ground through the pot and being lost. For this reason, guitars with humbuckers like Les Pauls use 500K pots to retain more highs for a slightly brighter tone and guitars with single coils like Stratocasters and Telecasters use 250K pots to add some warmth by slightly reducing the highs. You can also fine tune the sound by changing the pot values regardless of what pot value the guitar originally had.

Makes sense to me.

[acorec]

Originally Posted by Middleman

Pardon me for saying, guitar electronics are not AC, they are DC. Look it up. Now they end up in an AC environment which is the amp but prior to that. Nope.

Guitar signals are AC (Alternating Current) signals. DC (Direct Current) has no frequency component. The AC signal has an impedance as opposed to a pure resistance which means that resistance, capacitance and inductance have to be taken into consideration. Any change in 1 component of inductance can have an impact on frequency and harmonics of the frequencies. AC Theory is quite complex (in relation to a purely DC circuit) and it would take a while to calculate exactly what frequencies would be affected with a change in resistance, but the fundimental differences are in my post above. The only DC in guitar electronics would be in active components and that is another ball of wax as they say.

Peace MM

[acorec]

Since I have some time I realized I never answered your question fully.

A guitar pickup is a coil of wire wrapped around a magnet. When the string is plucked, the changing vibration excites a magnetic field (the pickup pole). This changing magnetic field induces a current in the coil of the wire and creates an alternating current across the two output wires. This electrical signal is what gets amplified later on in the pre-amp and amp stages. As you remember, the output of your amp to the speaker has no polarity itself. This is because it is an AC signal. Remember, a coil (transformer by another name) cannot pass DC current. DC Current by definition has a frequency of 0. It does not change, so a pickup coil would "see" nothing. The coil (transformer) will only pass AC current. Now, there can be AC current with a DC offset but this is only found in active electronics. The DC you might be thinking of is the 9v DC found in all stompboxes and active pickup guitars. This 9v is only used for powering the active op-amps and transistors that amplify the AC analog signal. Passive pickups have no DC offset or DC component and only generate AC current (and voltages).

[Middleman]

If acorec calls it, I believe it. I was thinking AC current like a wall socket is AC. Then my apologies regarding DC. I was thinking Active Electronics.

My experience with replacing volume pots has revealed some frequency alterations. That is why I mentioned it.

[ggunn]

Originally Posted by Middleman

ggun, find one piece of information that indicates that guitar electronics are AC, alternatiing current and I will apologize. This I gotta see.

Acorec, thank you for your explanation, that is exactly what I was indicating but did not explain out as eloquent as you.

What he said had nothing to do with what you said. He said...

...using higher value pots (500K) will give the guitar a brighter sound and lower value pots (250K) will give the guitar a slightly warmer sound. This is because higher value pots put less of a load on the pickups which prevents treble frequencies from "bleeding" to ground through the pot and being lost.

...which makes sense because the extra loading on the pickup from a smaller pot lowers the frequency response of the first order LC circuit made up by the inductance of the pickup and the resistance of the pot, producing a darker sound. In fact, he said exactly the opposite of what you initially said; you said that a lower value pot gives you a brighter sound. Here, I'll quote you:

As mention before the 1k pots are passing a lot of highs. I used these for years with solid state amps but when I went back to a tube amp, I went back to 250 and 500 pots on my guitars...I got tired of the super treble thing.

Beyond that, ANY audio signal is, by definition, AC (DC is an AC signal of 0 Hz). Capacitors and inductors are AC circuit components; to DC, inductors are shorts and capacitors are opens. The only DC in guitar electronics are the power supply nodes in active circuits, and most guitars don't have them. If there's no battery, there's no DC.

There's lots of different flavors of AC; I didn't say that you have to plug your guitar into a wall socket, fer chrissakes! ;^)

Look, I apologize if I've said anything that offended you. I'm an engineer (I have studied this stuff, although it's been a while), and I enjoy getting into technical discussions and getting to the bottom of things. I've been told that I can be a bit abrasive at times, and I guess that's true.

Peace,

[Light]

Originally Posted by ggunn

*except for a tiny amount of signal bleed to ground through the pot resistor. A lower value pot loses more signal to this effect, not less.

You just answered your own question, but you are forgetting one of the basic truths of audio. High frequencies are much more delicate than low frequencies, which means when a lower value pot bleeds off signal, it is taking more high frequency information than low, which is why a high value pot is brighter than a lower value pot.


Light

"Cowards can never be moral."
M.K. Gandhi

[ggunn]

Originally Posted by Light

You just answered your own question, but you are forgetting one of the basic truths of audio. High frequencies are much more delicate than low frequencies, which means when a lower value pot bleeds off signal, it is taking more high frequency information than low, which is why a high value pot is brighter than a lower value pot.

It's grand when we all agree, ain't it? Can we agree that it's about time to go grab a beer?

[ggunn]

BTW, when you guys said "1 k" (1000 ohms) did you really mean "1 M" (1,000,000 ohms)? This whole discussion would have made a lot more sense to me if that were the case.

At any rate, we all ran off talking about frequency response, but the OP was asking about his too-hot signal. I think (given what I've learned today) that changing from a 1 M ohm (if that's what he meant) pot to a 500 k would make his guitar sound a little darker, but wouldn't have much effect on amplitude or distortion.

[Light]

Originally Posted by boingoman

As far as volume affecting tone, it happens not from the volume pot, but the tone control and associated cap(s). For sure if you back the volume off on a Strat, you can get treble loss. But only because the tone pot and cap are still in the circuit.

Yes...and no.

That is certainly an issue, but there is a tone difference between different value volume pots as well. And that is before we even get into the whole high frequency loss as you turn the volume pot down. There is a whole other mod for that, which involves soldering a very low value cap (usually a .001mf or a 670 Pico fared) between the input and output on the volume pot. I don't like this at all, as it makes the overall guitar a bit brighter, which is not what I am looking for, myself.

Originally Posted by boingoman

I have seen (and done) a tone pot mod, opening it up and scraping the carbon off the track at the full up position, so the pot and cap are totally out of the circuit when the tone control is full up. No more treble loss when rolling off the volume.

Some Fender guitars have had this or a similar mod stock from the factory, where the goal is to bypass the tone circuit.

Fender sells a "True Bypass" pot, but again, I don't really see the need, personally. If I played country, then I would see it, but of course, I don't play country.


Light

"Cowards can never be moral."
M.K. Gandhi