Tone circuit issues :(

[icydash]

Hey guys, i've been using multisim to build my first tone circuit with treble, mid, bass, presence, and volume knobs. When i use the built in oscilloscope the volume potentiometer works and the bass potentiometer looks like it works, but the presence, mid and treble potentiometers dont seem to have any significant affect on the shape of the input waveform...did i make a mistake somewhere??? ideas??? I used an input voltage of .3 volts because i read somewhere that the average guitar pickup puts out between 100mV and 1V. The potentiometer farthest to the right is the volume, the one to the left of that is in series with the capacitor and resistor is presence, and to the left of that is my treble/bass/mid. The one switch in the circuit is for my bypass. I made this one myself, im an EE major so im trying to draft my own. I think i have the general idea right, give or take some values of resistors/caps here and there. The circuit is below... Thanks!





Oh yeah... Anyone know how i might add an LED indicator for when the circuits on as well?

[Gilles C]

The bass pot works because you use 60Hz for the signal generator. This frequency belongs to the bass region. You have to use higher frequencies for the mid and treble.

Check this program to see what frequencies you should use

http://www.duncanamps.com/tsc/

For the LED, I would change the bypass switch by a DPDT, and use the other contact to connect a dc voltage like +9V to the LED through a limiting resistor.

Oh, and I would change how you connected the bypass switch for when you are setting it to the off (bypassed) position. Right now, if the volume is at the minimum, it is 0 ohms, and you are applying this 0 ohm to the signal generator.

And welcome to the forum...

Gilles

[icydash]

wow thanks man i totally didn't even think about the input frequency lol thanks again!

[icydash]

What's wrong with applying the 0ohms to the signal generator in the bypassed position, isn't the input and output the exact same since there is no resistence between them and a good bypass?

[DuncanM]

What Gilles means is that when the output pot is set to minimum and you bypass the circuit, the pot will short the input signal to ground and you will get no signal passed to the output....

This is a bit of sloppy design because the input impedance of the next stage will be determined by the resistance of the lower section of the output level pot (the resistance between wiper and the earthed lug) - this will affect level and frequency response in bypass mode.
Better would be to switch the output side - you'll still have the input impedance of the eq in parallel with the input impedance of the following stage but at least it should be constant.

You'll also probably find that some gain recovery is required at some point...

[icydash]

What do you mean by "Better would be to switch the output side" ? Yeah i just noticed the loss in gain and i think im gunna add in another stage with an opamp and a potentiometer in the negative feedback so i can control the boost. Any ideas on a good opamp that wont distort for this?