Tele Tone Control Need Help

[vg3000]

I'm jumping into a tele project I've had on the table for a while. I'm having a problem, and I need to know if this is normal.

I have two pickups in it right now with normal 3 way switch (for now anyway). I put two push pull pots with the switches not being setup for the moment. Just the pots are being used both 500k.
In the neck I have a single conductor + sheild Humbucker and in the bridge I have a standard two wire tele pup.
All wired up like a stock tele using a .047 cap for tone. Wiring like this;

www.fender.com/support/diagrams/pdf_temp1/telecaster/0118000A/SD0118000APg2.pdf

The only thing I have done differently is add a 270k resistor to the bridge pup to ground to compensate for the 500k volume pot like shown here;

www.fender.com/support/diagrams/pdf_temp1/telecaster/0108000_02B/SD0108000_02BPg2.pdf

What's happening is the tone control only works till a little less than half way of the rotation and then it's completely off and not very usable at all. This to me is not how a tone control should operate, is this normal with this sort of setup? If not, what am I doing wrong and how can I fix it?

TIA!

[ChrisK]

?Is it wired like the first link (Tele 2 Pole 3-way switch) or like the second link (Strat 2 Pole 5-way switch)?

Are you showing the second link only to show that you have a permanent resistor from the bridge hot to ground?

A 270K resistor overcompensates for a 500K volume pot. If you were trying to realize an "effective" 250K resistance, you would use a 500K resistor in parallel with the bridge. When the bridge is selected, the 270K in parallel with the 500K pot presents an "effective" maximum load of 175K. Note that a 500K volume pot and/or 500K tone pot will have a different "effective" curve(s) than a 250K unit.

When one looks at the 500K volume, the 500K tone, and the 270K padding resistor, one realizes a 130K "effective" resistance.
This is close to the "effective" 125K from two 250K pots


I use "effective" in describing these issues since only in a most DC simplified and essentially incorrect interpretation from an AC circuit analysis perspective (- and this IS an AC circuit) does this even come close to reality.

To fully "see" the frequency response and drive level effect of different pot values, one must use an AC circuit analysis program such as pSpice.

When a 500K pot is used for volume and is turned down to "7" (where each side has half of the total resistance), the effective output resistance of the pickup(s) driving the cable is doubled compared to a 250K pot. In other words, assuming that the pickups have perhaps 3K of internal resistance (two are in parallel), the 250K volume pot has 125K from the pickup hots to the output jack, and 125K from the output jack to ground.

The Thevenin equivalent circuit of this is 1/2 of the AC signal thru 125K||125K + 3K , or 66K. The 500K equivalent is 250K||250K + 3K or 128K. The 500K volume pot will not be able to drive the amp as hard when it is turned down.

Audio Taper Pots - Not Really

What's happening is the tone control only works till a little less than half way of the rotation and then it's completely off and not very usable at all.

Which half way? From "0" to "5" or "5" to "10"?
I presume that it's "0" to "5" since you are using a 500K tone pot. If a 250K tone pot is at "10", the resistance is 250K. A 500K pot used as a tone control will be at 250K at "7".

Since you have a 270K resistor permanently across the bridge pickup, it will make the bridge pickup sound (always) darker, and will also make any combination with the bridge pickup in circuit sound darker.

Compared to a 250K tone pot, especially with the 270K across the bridge pickup, turning from "7" to "10" will likely have less to little effect.

Now, in a simplified view, I'm a big fan of using a 500K pot for tone with single coils since it IS down to 250K at "7" (still gives a lot of adjustment range from "0" to "7") and goes up to 500K at "10". This gives the option of more high frequencies if needed.

I'm not a big fan of 500K volume pots with single coild unless one knows what to expect.


Now, I suppose that you may have some other issue with your circuit that is causing the minimal tone control rotation, but it does seem to be related to component values.


I would also propose that this post be moved to "Electronics and Wiring"

[vg3000]

Hello Chris,

It's wired like the 3 way version. The only thing I added was the 270k resistor to ground like the 5 way.

What I'm getting is from about 0 to 3 I have fairly muddy bass that lightens up a bit at around 3. From 3 to about 5 you hear the normal bass to treble taper you hear in a normal tone control. Then from 5 up to 10 it's like the tone control is totally bypassed.
What's strange is you can almost hear a click as it kicks in or bypasses.
Have you ever heard any old Speedy West stuff with Jimmy Bryant (50's, late 40's)? Speedy used to get a wah effect going from his lap steel. You could hear it click in and click out very pronounced. That is exactly how this sounds, almost like a switch switching between mud and clean. (See Speedy West & Jimmy Bryant - Stratosphere Boogie. Great album btw).
I checked the pot to see if it was defective and it was not. I got a clean increase in ohms from 0 to 500k and back on a DMM.
Do you think the .047uf cap may have something to do with it? Maybe swap that out for a .022uf?

TIA

[ChrisK]

Changing the cap from 0.047 uF to 0.022 uF will increase the tone control cutoff frequency. Things will sound brighter, but not significantly. In conjunction with the inductive component(s) of the pickup(s), this will be about 1/2 octave.

A 0.047 uF cap is kind of much for the neck humbucker. Most of those use a 0.022 uF.