In the 50s setup, on the volume pot, the pickup is soldered alone to the right tab, looking from the back, and the capacitor is soldered to the middle tab and the other end of the capacitor is soldered to the left tab on the tone pot. This results in a higher output and the capacitor acts as a treble bleed. As volume is decreased, more high-end frequencies are maintained allowing you to play and a lower volume with more clarity. The relationship between the volume and tone controls changes too. They become more interactive with each other. As you decrease the tone control, the volume will decrease ever so slightly. Minute changes in tone will influence volume and output and vice versa.
When you use the middle position of the 3-way switch the pickups are wired together in parallel, so when both pickups are engaged, rolling down the volume of one even slightly while leaving the other fully open makes the latter much louder than its mate. Backing down just one of the volumes to zero shuts off the entire guitar.
Why is this? Because the two volume controls are not decoupled, they interact. With a passive circuit like this, it's just the nature of the beast. Consequently, the dual-humbucker guitars wired this way divides players into two opposing camps. The first doesn't consider this interaction a problem. It's simply part of the game—get used to it. The other camp regards this interaction as a system error and tries to eliminate it.
In the modern version, the pickup and capacitor are connected to the same tab on the volume pot, right looking from the back, and the other end of the capacitor is soldered to the middle lug on the tone pot. The Volume controls are now decoupled and work independanly.
The downside to this is when the pickups are wired this way they "see" less resistance, and the output impedance rises. This results in dramatic treble loss when you roll back the volume. It's an idiosyncrasy of passive guitar systems. When you turn down the volume, even just a bit, treble loss is not proportional, a small cut in volume creates a far greater loss in treble response. This is why many modern guitars can sound a bit muddy at lower volumes.
• Pickups don’t lose their high frequencies when turning down the volume. Pickup tone remains consistent.
• High frequencies tend to stay clear with the Volume Pot in it’s lower ranges.
• Pickup tone is punchier, more "in your face".
• Turning down the tone control can affect the pickup’s volume
• Adjusting the tone control will not affect your pickup’s volume.
• A smoother tone in general, which some players prefer.
• Turning down the volume control will send some high frequencies to ground, resulting in a darker tone overall. Many players try to fix this by using treble bleed capacitors on the volume control.
50’s wiring is probably more popular, we find many customers change their modern to 50’s but some like the way modern takes off some of the top end as they roll back the volume.
