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What effect does resistance have on impedance?

#2
I'm a bit confused by what exactly you are trying to figure out with your question?

The highest DC resistance I have ever seen in a pickup was like 30K. With that being said, putting the 250K or 500K pots parallel to the pickup is going to still be a very low resistance.

Say you had a 10K pickup and fed it into a 500K pot, that would be a resistance of 9.803K
 
#3
Another thing to note is that your resistance changes with the pot's setting.

Lets say you have a single volume control, with the output connected to the wiper terminal.

With the pot on "0", the resistance from output to ground is 0 ohms.
As you turn the volume pot up, the resistance between the wiper terminal and ground will increase, up until the point that the resistance of the pickup on the other side of the pot starts to bring it down, then it will go down toward the resistance of the pickup.

I just hooked up one of my Jazz basses to an ohm meter.
It goes from 0 ohms across the output jack with the knob on "0", up to about 120K ohms toward the middle of the rotation (linear taper, 500K pot btw) then down to around 8K on "10".

If you have more than one volume control, this resistance is getting varied against the pickup rather than the output, as the wiper terminal can only be wired to the pickups or the bass will mute when either volume is turned to "0".
 
#5
cassius987 said:
Let's say I have a single humbucking pickup with a volume and tone wiring harness. The two pots are each either 250K or 500K. Which setup has the higher impedance?

I ask because I have realized that lower impedance tends to sound better... thanks.
Click to expand...

You might be a little confused on your terms. When people talk about resistance, they are usually talking about resistance to DC current. The pots that you talking about there have a max DC resistance of 250 or 500 ohms. DC resistance is really straight forward because it doesnt change based on the signal.

Impedance is the resistance to AC current. Impedance is a pretty complex calculation because it is frequency dependant and is derived from two numbers including a new term "Reactance".

What confuses people is that pickups that have tend to have low Impedance have both low resistance to AC current and DC current. So you might hear of a "Low Impedance pickup that is wound to 1kohm DC resistance" ... thats actually two completely different items in one sentence. It would be more accurate to say "The pickup has a low DC resistance, and a low impedance."

Low resistance (and low impedance) pickups generally require a pre-amp because they are low output, where as higher resistance (and higher impedance) pickups dont need a preamp.

Now to answer your question as to which will have the higher impedance? I dont know, because I dont know what effect resistor/potentiometers have on AC current.
 
#6
KramerBassFan said:
Resistance, IS impedance....
Ohms = measure of resistance.
(Thats all I had to add, LINE6MAN pretty much explained it )
Click to expand...

GONGGGG... No--resistance is NOT impedance, not exactly. They are both measured in ohms, but they are separate concepts: impedance is a combination of resistance, capacitance, and induction. The reason the OP's question is a reasonable thing to wonder about is because you can't just look at a 250K pot and say the passive wiring harness overall has a 250K impedance.

Having said that, I don't actually know the best way to answer his question, and I'm hoping somebody who actually knows their stuff will pop in to help. :)
 
#7
svirfnebli said:
The pots that you talking about there have a max DC resistance of 250 or 500 ohms.
Click to expand...

250K and 500K...

FWIW, I referred only to resistance in my reply, because I'm really not sure how to answer the question, and I'm thinking the OP was talking about resistance with his reference to the pot values and the pickup.
cassius987, I don't think you really understand the difference between resistance and impedance. Your question is really nonsensical to those of us with a better understanding of electronics.

Also,
I ask because I have realized that lower impedance tends to sound better
Click to expand...
That's not really true. Low impedance outputs are usually able to run through long cable runs with minimal high end loss, but it's the nature of the signal and it's application that allows you to maintain your tone, not necessarily that the pickups/electronics have better tonal qualities.
 
#8
cassius987 said:
Let's say I have a single humbucking pickup with a volume and tone wiring harness. The two pots are each either 250K or 500K. Which setup has the higher impedance?

I ask because I have realized that lower impedance tends to sound better... thanks.
Click to expand...
to drill down to the nub of the question, the "impedance" will be whatever the pickup itself is.

250k pots will darken ("load") the pickup a little more, and 500ks will come closer to having no effect on the pickup, leaving in more treble, but that's about it.
 
#9
cassius987 said:
Let's say I have a single humbucking pickup with a volume and tone wiring harness. The two pots are each either 250K or 500K. Which setup has the higher impedance?

I ask because I have realized that lower impedance tends to sound better... thanks.
Click to expand...

The 500k setup will have the higher impedance.

However, your rule about lower impedance sounding better is not true. The effect of a volume pot on a pickup is to load it with the resistance of the pot. A pickup will have a certain resonant frequency and roll-off characteristic that is a result of the inductance, capacitance and resistance (including volume pot) of the total circuit. About the only way to REALLY tell which sounds better is to try both values. There is often a rule about 250k for single coils and 500k for humbuckers because the humbuckers are often two coils in series which doubles the inductance which doubles the pickup impedance. But it's just a rule not a hard and fact law of pickups. It all really depends upon the actual values of a given pickup. Your ears are the final judge.
 

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