Bass EQ

[Radamus]

I have a passive bass guitar, and it occurred to me that I could just make some active electronics in a pedal. I looked at the EQ section of the schematics, but I couldn't figure out how to make them work for bass, as the valued are going to be lower. I may be mistaken, and I probably am to some extent. Is there any schematic specifically for bass or does anyone have some documentation that could explain to me how EQ circuits work?

Also, does anyone have an EQ circuit schematic from an active bass? I only need Low, middle, and high, but I would like to at some point do five separate knobs.

Thanks in advance, and I'm sorry for the newbie questions.

[George Giblet]

An example is the Tobias preamp, under "Tobias Active Bass Circuit Schematic" here:

http://www.musicyo.com/tech_info.asp

[Mark Hammer]

In general, the capacitor values that set the frequency range to be controlled can be adjusted using the rule of thumb that doubling values moves them down an octave, and halving values moves them up an octave.

For instance, you will note that in the schematic shown here: http://www.generalguitargadgets.com/pdf/ggg_eq6b_sc.pdf  the caps used to set the range for "125hz" (and I put it in quotations because it is nominally 125hz, not a guaranteed 125hz, given the various component tolerances) are roughly half the value (or closest common-value equivalent) of those used for the 62.5hz band.

So, what you can do is build a circuit like that shown, and work out the corresponding cap values that target the frequency bands you wish to control.  Of course, whether a resonant EQ like this one provides the sort of tonal control you want or need is a separate issue.  Personally, I think the ideal is a fixed-range low-end shelving stage, two semi-parametric resonant stages, and a sweepable 2-pole lowpass filter (with resonance control) for adjusting the high end provides the most flexibility in the smallest package, but that's just me.

[Kolloi]

What Mark Hammer said, and also use this formula to get the frequency cutoffs you want:

frequency = 1.6 / ((Resistance in Ohms) * (Capacitance in Farads))

[Radamus]

MArk Hammer, I would really like to know how to do all of those things you recommended. Unfortunately, I got lost in the language. I am really new to pedal making. I have successfully constructed two and I have a nonfunctional big muff sitting on a breadboard.  I would like to make an EQ and I can probably figure it out, but I am completely unfamiliar with types of EQ or low-pass filtering, etc. Can you shed some light on this?

Thanks.

[Renegadrian]

I'd suggest you to look around the web for amps schematics, and/or try what Dano does here ---> http://beavisaudio.com/Projects/BigMuffToneControl/ socketing the components and experimenting...

[Radamus]

I've left this topic here for a while, but I'm ready to return to the topic. I like the GGG design a lot. It seems to be easy to understand and it offers me options. I still don't understand what all the types of EQ are, but I'll go with a straight ahead one for now.

I would like to modify this for a bass and I would like to modify it to be an odd number (no real reason, but the odd number gives me the nice V-shape option). Would seven cause me to need more power? I don't know how that works.

Which frequency ranges would I need? I have a four string bass right now, so I'm guessing that means I should have a center around a G or E. Would that be closer to the 31.3hz?

How does the 1.6/R*C equation work for this model (if at all)?

I don't understand the cut and boost symbols (the double arrows). Are these a component or just a marker?

What op-amps should I use?

Would it be logical to try to combine this with a bass paralooper?

Would it be difficult to use the sliding potentiometers instead of rotary?

[Dragonfly]

You might look at the ROG Tonemender ...it may need a bit of tweaking for bass, but would, at the very least, make for an excellent starting point.

[Radamus]

I'm not sure how to tweak anything for bass yet. I haven't seen an example that really fits the 1.6/RC formula, so focusing on certain frequencies would be a bit tough,