Wiring Capacitors

[MattSA]

I have been working on minor rewiring of a Washburn guitar over the past two years. I am comfortable with soldering and wiring, but have run into problems with my capacitors. The Washburn's sound in particular relied heavily upon the capacitor. Unfortunately when I replaced its humbuckers I did not make a schematic of the capacitor wiring before removing the parts. I successfully rewired after several configurations between the tone and volume pots and the capacitor; however I did not make a schematic of the wiring again, and have removed the components so I can refinish the guitar.

I find it difficult to understand how the wiring works in the first place - if the volume pot reduces volume, why doesn't the tone pot also reduce the volume? They are both the same type of pots. I am fairly certain the volume pot reduces amplitude, while the tone pot changes the frequency of the signal. If I wire the volume pot before the tone pot, I can reduce the volume, but won't the tone pot also reduce the already lowered signal? This makes me think the tone pot should be wired first. I have looked at many, many schematics doing this wiring differently. I have tried many of them and most leave me with only the volume pot changing the signal. I have also seen wiring where there are two live leads from the tone to the volume pot, one with the capacitor and one without, but recombining the signal reduces the effect of the tone reduction. Can someone provide me a link or clear advice to how I should handle this wiring dilemma?

MattSA

[curtisa]

Moved to the Electronics Chat section of the forum for better housekeeping.

[curtisa]

On 9/9/2018 at 5:48 AM, MattSA said:

Can someone provide me a link or clear advice to how I should handle this wiring dilemma?

Was there something special about the wiring in this particular guitar that you're trying to recreate? Can you google some Washburn model numbers to see if the original wiring diagram is out there somewhere?
 

On 9/9/2018 at 5:48 AM, MattSA said:

I find it difficult to understand how the wiring works in the first place - if the volume pot reduces volume, why doesn't the tone pot also reduce the volume?

The volume pot is always wired in what is known as a variable voltage divider. It's the standard way of doing volume control, whether it be a guitar or a hifi stereo. The signal you want to control gets hooked up to one side of the pot and ground to the other side. The variable wiper in the middle of the pot then gets swept from one extreme to the other, able to 'listen' to either the full signal or silence (ground) in whatever ratio you move the wiper to.

The tone circuit usually just shunts a portion of the signal to ground via the capacitor, the pot just acting as a throttle to send more (tone at zero) or less (tone at ten) signal through the cap. The use of the cap is desirable in that the amount of signal it 'lets through' is dependent on the frequency content of that signal, naturally allowing more highs to pass than lows. The tone pot can (sort of) reduce volume, but only to a certain range of frequencies.

 

On 9/9/2018 at 5:48 AM, MattSA said:

If I wire the volume pot before the tone pot, I can reduce the volume, but won't the tone pot also reduce the already lowered signal?

Sorta. The tone pot can be either before or after the volume pot and essentially still work the same. But depending on where it is placed has an effect on how the tone control interacts with the volume. One control will cross-load the other in different ways (eg, treble roll-off as you wind the volume pot down, tone control operation affecting overall volume). It usually boils down to which compromise you can live with.

[MattSA]

Thanks curtisa. Although I understand the middle statement above partially I am still a bit confused. I am working under the assumption that when I purchase a pot (specifically for a guitar) it can be used as either a volume pot or a tone pot. I am also aware that a capacitor siphons off part of a signal - storing it temporarily, but not returning it. When I look at various schematics, the capacitor is wired in different places. Ideally I would like to wire the volume pot after the tone. Will I still receive full volume after the signal has passed through the tone pot? The tone pot should be changing frequency (sound of the signal), while the volume pot should be changing the amplitude (loudness of the signal ). Should I wire the switch to the tone pot, wire the cap to the tone pot lead out, then directly to the lead in of the volume pot? This would not reduce the volume, before the signal gets to the volume pot?

 

[curtisa]

1 hour ago, MattSA said:

When I look at various schematics, the capacitor is wired in different places. 

Got particular examples?

Nearly all tone controls in guitars will be exactly the same - a capacitor in series with a pot, the whole shebang strapped across the signal wire and ground. Swapping the positions of the cap and pot makes no difference.

 

2 hours ago, MattSA said:

Ideally I would like to wire the volume pot after the tone. Will I still receive full volume after the signal has passed through the tone pot?

If you are in the habit of playing with the tone pot full up most of the time, it actually makes no difference whether you place the tone pot before the volume pot or after it. You will receive full volume after being tone'd or before tone-ing.

Note also that the signal does not 'pass through' the tone pot, rather it gets 'weighed down' by the tone pot.

 

2 hours ago, MattSA said:

The tone pot should be changing frequency (sound of the signal), while the volume pot should be changing the amplitude (loudness of the signal ).

Both controls do this to the best of their ability given that there is some degree of interaction between the two. In a passive guitar this is unavoidable. If you want true segregation of volume and tone controls you need to install active preamp circuitry.

As a general rule:

• Volume first, tone last = less treble roll off as the volume pot is rolled down if tone is at maximum, but tone control usage affects the overall output more, particularly at lower volumes.
• Tone first, volume last = tone control behaves more consistently at any volume, but volume control exhibits higher degree of treble roll off as you wind it down.

 

3 hours ago, MattSA said:

Should I wire the switch to the tone pot, wire the cap to the tone pot lead out, then directly to the lead in of the volume pot? This would not reduce the volume, before the signal gets to the volume pot?

I'm having trouble visualising what you're asking. You might have to draw a diagram to explain it better.