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GuitarNutz 2 :: Taming the Tone Beast :: Electronics and Wiring :: Modern and 50's Wiring
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AuthorTopic: Modern and 50's Wiring (Read 3,239 times)
JohnH
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Modern and 50's Wiring
« Thread Started on Feb 11, 2008, 3:51pm »
(Stickied..... instantly! Too good to let this drop down at all. Thanks, John!)



OK, modern wiring and 50’s wiring:

This choice comes up frequently on forums wherever Les Pauls are discussed. It relates to whether the tone controls are wired before or after the volume controls.

Here is a schematic, using 5Spice, representing one pickup on a modern LP, with a PAF humbucker pickup:

[image]

It uses 500k pots, and I have represented a short guitar cord of about 10’, without adding a treble bleed cap to the volume control, since that would be a non-standard addition (a good addition IMO, but that is a different story)

Here it is, wired 50.s style:

[image]

At full volume, both are identical in response. This shows the frequency response as the tone pot is reduced in 10 linear steps:

[image]

Note the last step, from 50k down to 0k, would represent 0-1 on a linear pot but 0-5 on a log pot, which shows why a log pot is better for smoothing out the response. You can also see the initial resonant peak, when at full volume and tone at 10.

The differences between modern and 50’s wiring start to occur when volume is reduced. The following have the volume pot set at 50%, which is 5 on a linear pot and about 7 on a log pot, resulting is a general 6db volume reduction:

Modern wiring, with 50% volume, tone pot 0-10:

[image]

50’s wiring, with 50% volume, tone pot 0-10:

[image]

Now you can see the difference. At full tone, and 50% volume, the 50’s wiring is in fact slightly brighter, which is due to it loading the pickups less. However, this does not compensate for the loss of the initial resonant peak. This extra brightness at reduced volume with full tone is the main reason some advocate 50’s wiring.

But as the tone is reduced, while the modern wiring acts fairly consistently on the treble, the 50’s wiring starts to cut deeply across all the frequencies except the very lowest, acting more like a volume control. The reason is that with modern wiring, the tone control acts consistently on the pickups, while with 50’s wiring, it is acting through the resistance of the volume control, resulting in it seeing a variable impedance, cutting much more deeply when the volume pot is reduced.

(Ill leave that last paragraph for a while, but if I think of a better way of saying it I’ll edit it later!)

This inconsistent tone response is why I would prefer modern wiring.

Cheers

John
« Last Edit: Feb 11, 2008, 5:14pm by sumgai »Link to Post - Back to Top  IP: Logged
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Re: Modern and 50's Wiring
« Reply #1 on Feb 11, 2008, 5:13pm »
John,

First, thanks! This answers the recent questions of several newer members. I trust that they will see this thread, and ask questions here, as appropriate. :)

A bit more of a deep explanation (emphasis added):
Quote:
But as the tone is reduced, while the modern wiring acts fairly consistently on the treble, the 50’s wiring starts to cut deeply across all the frequencies except the very lowest, acting more like a volume control. The reason is that with modern wiring, the tone control acts consistently on the pickups, while with 50’s wiring, it is acting through the resistance of the volume control, resulting in it seeing a variable impedance, cutting much more deeply when the volume pot is reduced.

Actually, if the impedance were to be increased (which it isn't, in your example (Solving the RLC equation will show that.)), the low frequencies would tend to be allowed to pass, and not hindered. Let's look more closely at the 50's diagram, and see if we can't figure out why the tone control cut much more deeply than anticipated.

Note that the upper leg of the volume pot also forms an RC circuit with the 130pf cap (the internal pup capacitance). Since that RC time constant changes with the rotation of the volume pot, you now have not one, but two tone circuits in play! Since one is in series with the other, the result will be the downward movement of the -3dB point, something that ordinarily does not occur in simple tone controls. In short, you now have a state-variable low-pass filter. It certainly is 2nd order, until that last step - that's a doozie! :P

For the ChrisK-inclined aboord here, this kind of complex analysis is ratiocentric, but it yields more readily to vector analysis. Or maybe that's just the way my mind works, I dunno. (When it is working. These days, it's hard to tell what it's doing! :o ;))

HTH



sumgai
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