You may have noticed that as you roll off volume you lose the treble end of your sound faster than the low end and you end up with a dark, muddy tone. There is a physics-related explanation, involving relative resistance and capacitance between potentiometers and pickups, but to be honest we don’t need to go into that here to get a practical understanding of the problem. Suffice to say that, as they are brought into play to reduce gain, volume potentiometers work raise resistance, creating what’s called a ‘low pass filter’ – low pitch is allowed to pass through and high pitch is filtered out of the signal to a higher degree.
This is more of an issue with single coil pickups than humbuckers and some people don’t ever notice it because they have their guitar turned up to ten all the time (that’s me!). However, if it’s an issue for you, the way to resolve it is to employ a high pass filter which bypasses the volume potentiometer in the form of a treble bleed mod. As the name suggests, a high pass filter is the opposite of a low pass filter and allow through only high end pitch. This is achieved by placing the filter between the ‘in’ and ‘out’ lugs of the volume pot (the ones that aren’t connected to the back of the pot). It’s an easy mod to achieve as nothing else needs to be de-soldered.
There is a potential drawback with treble bleed, in that the guitars tone may become too bright when the volume is rolled off. But there are different varieties of treble bleeds so you can experiment with different schemes and values. There are three different treble bleed mod options (see image, from left to right).
1. A capacitor on its own, usually of a value between 500 – 1000 picofarads
2. A capacitor of between 1 – 2 nanofarads in parallel with a resistor of a value between 100 – 350k
3. A capacitor in series with a resistor (values below)
The capacitor on its own might create too much brightness for you as you roll off volume. Adding the resistor in parallel, the Seymour Duncan scheme, will attenuate the amount of treble pitch being passed through. Option 3, sometimes called the Kinman treble bleed (after its creator Chris Kinman), employs a resistor and a capacitor in series and is in my opinion the most useful solution (Fender agree and use it in their guitars). However, you might want to use option 1, a capacitor on its own, in a bridge pickup where you want to maintain the bite of the sound as you roll off to a greater extent. PRS use a cap only in their guitars. It’s all very subjective and in the ears of the beholder, so use whichever one you perceive to be the best for your guitar.
Values of the caps and pots are important, but within reason there’s no harm in experimenting. A lower value capacitor allows more highs through and a higher value resistor prevents them from going through. Chris Kinman recommends a balance of a 1.2nF polyester capacitor and a 130k resistor and recommends that you should match a low value cap with a low value resistor (or high with high).
Despite reports to the contrary, you will find that different types of capacitors impart different qualities to tone. However, you don’t need to spend a fortune on Russian military paper-in-oil caps or ‘orange drops’ to get your sound (although in some guitars they will be the best tone caps to use). Inexpensive, low voltage film caps of any kind will usually work well (I like polystyrene). Physically larger sized caps will get in the way, make it harder to wire up the pot, and can create ground issues if they make accidental connections in an overcrowded control cavity.
Use a hot iron and heat sink (a crocodile clip or similar) when you solder in the treble bleed. It will help prevent the heat damaging the capacitor.
I have also owned a Standard 25 from this Vox range and it wasn’t anywhere near the Custom 24 in terms of quality. I have never seen a Standard 24 in the flesh but it looks like a lower end Custom with its set neck, plastic nut and simpler electronics as well as a strat-style tremolo bridge.
I hope this information is helpful in achieving your ideal sound.
This brings us on to the most contended area of the subject of capacitors – materials. Capacitors can be constructed of a few different types of materials: paper-in-oil (PIO); film (polypropylene, polysyrene or polyester); and ceramic are the most usual formats. There are two ends of the spectrum here. Some people will say that only old-style PIOs such as ‘bumblebees’ sound good in guitars. Alternatively, it is often argued that it makes no difference what type of material a capacitor is made of and that it is only the value that counts. This is a belief most strongly held by trained electronics experts. The truth of the matter lies somewhere in between.
While it is true that in an electrical circuit the material of a capacitor has no relevance in its ability to act as a capacitor in the traditional sense, and the electronics boffins can produce formula to demonstrate this, a capacitor in a guitar is part of a signal path, not an electrical circuit. In other words, it isn’t doing at all the same job in a guitar. What is passing through the wires in your guitar is a current which is acting an analogue of the vibration of the strings, a conversion of very complex frequencies, overtones and tones into an electrical signal, which will be converted back into sound by your amplifier. The capacitor filters out some of those signal frequencies via the material of its construction, and the frequencies and tones that material allows though and removes from the signal path can vary. You can check this for yourself by setting up some wire and crocodile clips and connecting different types of capacitor of the same value to a pot. Provided the caps are genuinely of the same value (which can be checked beforehand with a meter) subtle differences in tone can be heard. Some people will argue that this is ‘confirmation bias’ (you expect to hear something and you do) but I have blind tested this with clients.