Instructables

Bass (guitar) signal spilt + combine

Hello
I have been thinking about a project that I would like to try. The idea is that I would like to be able to take the signal from my bass guitar and split it in two (configurable how much signal in each, but the sum should be 100%), apply an effect to one of the lines and then combining the two signals again having only applied the effect to some of the signal while carrying the clean signal through. This way I could apply e.g. distortion to only 20% of the signal.

I thought that I could control the volume simply by putting an resistor in the signal line, but this gave quite some noise. This is my first attempt at building electronics for instruments, but have some experience with electronics in general.

Hope you can help me with a couple of questions:
1) Shouldn't you be able to lower the signal simply by resistors? Should you use any specific resistors for audio?
2) Is it possible to recombine two audio signals and can you just put the wires together?

Kind Regards
Brian



jim5150jvc9 months ago

This is a good article on that subject. It discusses the advantages of splitter transformers

http://whirlwindusa.com/support/tech-articles/microphone-splitters/

gmoon1 year ago
Yes, resistors can lower signal volume when they are connected as a voltage divider. Your bass guitar has a volume control knob, right? That potentiometer is wired as voltage divider, as are almost all volume controls. It's simple--one end is the signal, the other end is GND, and the center wiper is the output of the divider...

A resistor in series with an audio signal increases it's output impedance. Higher output impedance audio sources are indeed more susceptible to noise. The resistor would attenuate the signal, but not necessary make it less loud (it would limit current, but not change the peak voltages by itself). Wired like that, the resistor might make the signal less loud, but it would be due to interaction with the input impedance of the next stage (and that will vary).

Two audio signals can be combined if a resistor is added to each; that's essentially called a passive mixer. That will attenuate your signal somewhat; again--how much depends on the input impedance of the next stage.

The alternative is to use an active mixer...
FatMooseHenry (author)  gmoon1 year ago
Hey, thank you for your answer, it helped a lot :) I'm going to look into it in a few days,

About the voltage divider... I know that it is the ratio between the resistors that controls the signal, but what resistor values should I aim to use? Is it better to use large or small values? High or low current?
There are no "hard rules" here--just common sense guidelines, based on your setup. Remember, a POT (volume control) is a voltage divider...you don't need a fixed resistive divider.

Considerations:

What is the output impedance of the bass pickups? Are they active PUPs?
What are the volume/tone POT values used with the existing pickup?
Is the signal splitter passive or active?
Is the mixer passive or active?
What is the signal strength and output impedance of the effect?

Might be necessity to use an active mixer, because pickups are likely to be much higher impedance than the output of the effect, generally speaking.

With active pickups a passive mixer might work.

Of course both the output and input impedances of effects vary widely, so an active splitter (or just a booster) also (or instead) might be necessary.

You can experiment with with this all passively, but I'm guessing that you'll either need a boost before the signal split, or an active mixer after... That's the rub--the in/out impedance values for guitars, guitar effects and amplifiers really interact...a LOT.