OT: guitar output impedance

[valdiorn]

Is it just me, or is this just not right??

http://alexplorer.net/guitar/mods/trebboost.html

I've been trying to understand why the f*ck a larger pot would give you more brightness. What capacitance is it that's interacting with the pot that causes this? (Because if it's the cable capacitance then this is just wrong :S )

also he says "Second, your output is stronger." .... is there any merit to this statement??

Can somebody take a look at that and tell me if it's correct or just a bunch of bologne, and if it's true, then explain it to me like the retarded monkey I seem to be (not understanding this is really making me angry )

thanks in advance

[davidallancole]

The output can be stronger.  The voltage division between the coil and the load (i.e. volume knob, tone controls) cause a higher voltage to be developed across a higher resistance.  This is true.  I took the volume and tone controls out of my guitar and hooked the pickup straight into a 1meg load on my amplifier.  The output was definitely higher when the amp was set to the same volume.

[Paul Marossy]

Using larger value volume/tone pots decreases the amount of signal that is always being shunted to ground and therefore the ouput voltage is greater - which means that your output will be louder, and somewhat brighter because more high frequencies are able to get thru to the output.

By definition, impedance is a measure of the apparent resistance posed by an electrical circuit to an alternating current (AC). You also have some capacitance and reactance as well in an electric guitar. They are three seperate things that conspire together in a high impedance circuit like passive guitar pickups to make you pickups sound "muddy". Cable capacitance is an external factor, which also plays a role in the overall scheme of things.

I myself don't like overly bright pickups. I like a fat tone with clarity, and yet not harsh. I know I wouldn't like what is suggested in that link, it would be way too harsh for my liking. If I was that bothered by all this, I'd rather go with active pickups...

[valdiorn]

Ok so I've thought about this a little more...

At maximum volume there is less current going through a large pot (to ground) then there is with a small pot, so you have more current going to the amp, and less treble sucking... I can see that now
...but set the volume control halfway down and you're sending the signal through a massive resistance (some people talk about using 1meg pots for volume), maybe 500k at half volume, that's going to suck some serious treble out of your signal when you couple that with all the parasitic capacitance in the cable...

[Paul Marossy]

Ok so I've thought about this a little more...

At maximum volume there is less current going through a large pot (to ground) then there is with a small pot, so you have more current going to the amp, and less treble sucking... I can see that now
...but set the volume control halfway down and you're sending the signal through a massive resistance (some people talk about using 1meg pots for volume), maybe 500k at half volume, that's going to suck some serious treble out of your signal when you couple that with all the parasitic capacitance in the cable...

That's why people put "treble bleed caps" on the volume controls. 
http://www.diyguitarist.com/Guitars/VolumeTrebleMod.htm

[biggy boy]

Also another reason to keep the volume control on your guitar turned all the way up and use the volume control on the amp.
When applicable of coarse IE: practicing.

[R.G.]

Ok so I've thought about this a little more...

At maximum volume there is less current going through a large pot (to ground) then there is with a small pot, so you have more current going to the amp, and less treble sucking... I can see that now
...but set the volume control halfway down and you're sending the signal through a massive resistance (some people talk about using 1meg pots for volume), maybe 500k at half volume, that's going to suck some serious treble out of your signal when you couple that with all the parasitic capacitance in the cable...

The culprit is actually the inductance of the pickups, which can be two to four HENRIES; the impedance of an inductor actually goes up with frequency.

[Paul Marossy]

The culprit is actually the inductance of the pickups, which can be two to four HENRIES; the impedance of an inductor actually goes up with frequency.

Isn't it made worse by a volume control turned down 1/2 way, though? That's also adding some resistance in the signal path, adding to the effects of inductance, isn't it?

This is an interesting page to read for anyone interested about how guitar pickups work: http://buildyourguitar.com/resources/lemme/

[biggy boy]

This is an interesting page to read for anyone interested about how guitar pickups work: http://buildyourguitar.com/resources/lemme/

That's actually a good site for learning how to build guitars too!
I used his downloadable book to learn how to make my guitars.
I've made 4 guitars and 2 basses thanks to his book.
It's 234 pages and covers just about everything you need.

Glen

[valdiorn]

You guys always have an answer, thanks alot

I just haven't really looked into how pickups and guitar circuits behave exactly, and I was trying to help a friend with this but I didn't have any answers to give him and it drove me crazy