How to Build a Guitar Stompbox Circuit to Simulate Cable Capacitance Effects

Hello there.

First of all, I am not an EE but I have some Computer Engineering experience. Please let me know if this is not the correct place for someone of my experience to ask a question.

I play electric guitar and noticed that the guitar sounded different when I used different cables. Had a look around and it looks like the capacitance of the cable is the culprit.

The complete circuit of the guitar->cable->amplifier creates a low pass filter because of the interaction of the pickups(EM Inducers)/tone control circuit(Capacitors and resistors)/capacitance of cable/amplifier circuits(not sure if there is a buffer in all amplifiers, old tube amps are still in common use).

You can avoid the effect of the LPF by using a cable with an extremely low farads/foot rating.

Here is a site I found that talks about cable capacitance.

Shootout Guitar Cables

With a cable with a low enough capacitance the cutoff frequency is too high to be noticeable.

However, sometimes the frequency response resulting from the use of a high capacitance cable is desired.

The main electrical engineer for Gibson guitars in the 70s wrote the analysis in the following link.

Bill Lawrence on Cables

In the linked article he states that the effect of a cable with a high capacitance could be duplicated by using a capacitor with an equivalent capacitance.

I can probably get the desired effect by purchasing a parametric EQ and placing it between the cable and amp in the signal chain but that stompbox costs about $180 Canadian.

I would like to build a stompbox placed between the cable and amplifier with a rotary switch that selects between several capacitors and a direct line. I assume that the capacitor has to be placed in parallel with the cable in some way to alter the capacitance of the circuit but I can't figure out how to design the circuit.

I know that it is probably a basic circuit to design but Analog circuit design is the reason I switched to computer engineering in 2nd year.

Thank you for any help you can provide.

Hello! This is definitely the right place to ask questions like this.

To design a stompbox that emulates cable capacitance, you can use a simple circuit that consists of a capacitor in parallel with a switch. The switch will allow you to select between different capacitor values, which will emulate the effect of using different cables.

Here’s a basic schematic of the circuit:

`
Guitar Input -> Capacitor + Switch -> Amplifier Input
`

The capacitor should be chosen to have a value that is similar to the capacitance of the cable you want to emulate. You can experiment with different capacitor values to find the one that sounds best to your ear.

As for the switch, you can use a rotary switch with multiple positions, each corresponding to a different capacitor value. You could also use a toggle switch with two positions, one for the direct line and one for the selected capacitor value.

It's important to note that while this circuit will emulate the effect of cable capacitance on the guitar signal, it won’t completely replicate the complex interactions between all the components in a guitar rig. However, it can still be a useful tool for achieving a desired tone.

I hope this helps! Let me know if you have any further questions.

 

Hello! This is definitely the right place to ask questions like this.

To design a stompbox that emulates cable capacitance, you can use a simple circuit that consists of a capacitor in parallel with a switch. The switch will allow you to select between different capacitor values, which will emulate the effect of using different cables.