G&L passive tone circuit question

[ikay]

Some G&L passive tone controls have a 6.8k resistor following the tone cap before it goes to ground (see link below). Can anyone tell me what effect this resistor has on the tone compared with a standard tone control (without the resistor). Thanks

Link Removed

 

[Crater]

It keeps the tone control from going all the way to "zero". With a normal setup, turning the tone all the way down connects one side of the tone cap directly to ground, with the this scheme, turning the tone to all the way down and there's still a 6.8K ohm resistor in series with the cap before ground. Since the tone cap is a larger than standard size, this is probably done to get a better range on the tone control. It would probably sound very dark and muffly without the 6.8K resistor when the tone was turned all the way down.

 

[Handyman]

It keeps the tone control from going all the way to "zero". With a normal setup, turning the tone all the way down connects one side of the tone cap directly to ground, with the this scheme, turning the tone to all the way down and there's still a 6.8K ohm resistor in series with the cap before ground. Since the tone cap is a larger than standard size, this is probably done to get a better range on the tone control. It would probably sound very dark and muffly without the 6.8K resistor when the tone was turned all the way down.

Yup, that's what its for. That little resistor gives you a useful sound across the entire range of the tone pot's rotation.

 

[ikay]

Thanks and that's interesting. With a regular tone setup (no resistor) connecting the cap to ground creates a slight boost at the lower frequency point (determined by the value of the cap). I can hear this in both my old Fenders - the tone gets darker the more you turn it down but when completely rolled off it brightens up a bit. With a .47 cap the fully rolled off tone is actually a bit more articulate and usable than some of the points in between. So I guess the G&L circuit just gets steadily darker with no freq bump when fully rolled off. Cheers

 

[SteveCS]

It keeps the tone control from going all the way to "zero". With a normal setup, turning the tone all the way down connects one side of the tone cap directly to ground, with the this scheme, turning the tone to all the way down and there's still a 6.8K ohm resistor in series with the cap before ground. Since the tone cap is a larger than standard size, this is probably done to get a better range on the tone control. It would probably sound very dark and muffly without the 6.8K resistor when the tone was turned all the way down.

Yup, that's what its for. That little resistor gives you a useful sound across the entire range of the tone pot's rotation.

This ^^

The Fender Greasebucket has a 4.7K resistor that serves the same purpose. In terms of the response curve, when the cap is grounded, there is a resonance between the cap and pickup coil which gives that boominess with the tone control backed right off. You don't get that with the resistor in place. It is only effective over the last few % of the pot and you can get the same non-resonant effect by not quite backing a standard tone control all the way off. You can change the resonant frequency by using different cap values, but the result also depends on the inductance and DC resistance of your pickup. I have two tone caps (0.022uF, 0.047uF) which I can also combine to give 0.069uF. All provide useful tones. Since yesterday, I also have a switchable Greasebucket which gives yet another set of useful tones. What would you do with these pots/switches? | TalkBass.com

 

[Handyman]

An interesting counter point to this approach is what the Stellartone Tonestyler does - basically a zillion position rotary switch that selects between either no cap or lots of different cap values directly between the signal and ground. No resistors at all.

The Stellartone approach gives you the resonance hump at all settings, as opposed to the 'extra resistor' approach, which gets rid of the resonance hump.

 

[SteveCS]

An interesting counter point to this approach is what the Stellartone Tonestyler does - basically a zillion position rotary switch that selects between either no cap or lots of different cap values directly between the signal and ground. No resistors at all.

The Stellartone approach gives you the resonance hump at all settings, as opposed to the 'extra resistor' approach, which gets rid of the resonance hump.

Good point. I have found that the resonant hump with a 0.022uF cap gives a really sweet and 'vocal' character to the tone whereas at 0.069uF it is really dark and 'dubby'. Perhaps I got lucky in that is works well with my particular pickups, and it might not be so good with others. At the same time, it is nice to have the option to turn it off on a switch or limit the amount of top cut with a pot.

I suppose the next step up in the resonance stakes is the varitone, which places an inductor in series with the caps, but that is another discussion.

 

[ikay]

It just seems a bit curious to engineer out the resonant bump which can be a useful tone option (although probably not that useful with a .1 cap) and is easily avoided by just not turning all the way down. The added resistor takes something away but offers nothing in return! Thanks for the replies

 

[SteveCS]

It just seems a bit curious to engineer out the resonant bump which can be a useful tone option (although probably not that useful with a .1 cap) and is easily avoided by just not turning all the way down. The added resistor takes something away but offers nothing in return! Thanks for the replies

On the face of it I would agree, but I guess it means you can get there without any fiddling around - just nail to pot to the bottom and you are there - so having it as a switchable option makes sense from a live perspective.