# Circuitry Project help?

• 09-06-2003
doubleanti
Circuitry Project help?
Hey folks. I'm pretty sure some of you here are circuitry buffs and maybe you can help me out! I'm trying to design and build a graphic equalizer which can also change the center frequency and bandwidth of the passbands for the transfer function. (Making changing the sound quality of my guitar output very flexible, yes? =)

I have the choice to do the following...

Firstly, initially I thought perhaps I should use op-amps for the equalization part. But it occurs to me that if I can superimpose a band reject filter with a bandpass filter, perhaps I can forego having to power the circuit if I'd used op-amps. Furthermore, the amplication of the voltage would happen in the guitar amp itself anyway so perhaps it is better.

Either I can put the filter before the eq, or the eq before the filter. If I were to have amplified the input voltage first, perhaps we can get a better one-to-one relationship on output (ie less noise since it's scaled up). Or maybe I should amplify it, filter it, and then scale it back down? And also, I suppose I'd have to use two different sets of inductors and capacitors if I were to superimpose a bandpass and band reject filter's output voltages, yes? (I was looking at the schematics for both and it dawned on me that if I were to just take the voltage across the resistor, capacitor, and inductor, it would just be the input voltage without a transformation, hehe, silly me...) At any rate, can anyone shed some light?

Another question I have which some may somehow know, else I will continue my research is the following...

Is the voltage frequency the same as the mechanical frequency, and the same as the sound frequency from the guitar strings thru the pickup? I would assume so since the string would oscillate a magnetic field at the same frequency it is mechanically oscillating.

Thanks for any help! Can't quite find a board as quick and nice as this for this stuff, will keep looking! =)

Sincerely,
doubleanti
• 09-06-2003
RobR
Re: Circuitry Project help?
Quote:

Originally posted by doubleanti
I'm trying to design and build a graphic equalizer which can also change the center frequency and bandwidth of the passbands for the transfer function. (Making changing the sound quality of my guitar output very flexible, yes? =)

That would be a parametric equalizer, if I'm not much mistaken. Very versatile indeed.

Quote:

Originally posted by doubleanti
Is the voltage frequency the same as the mechanical frequency, and the same as the sound frequency from the guitar strings thru the pickup? I would assume so since the string would oscillate a magnetic field at the same frequency it is mechanically oscillating.

AFAIK, yes.
• 09-06-2003
doubleanti
Ah I see... so they already have this kind of thing eh? Shucks now I'm tempted just to buy one... hrm... and perhaps having 24 knobs for 8 bands would be really tedious... but it would still be fun. Meanwhile I'll try to find new and interesting ways to rewire my guitar to get a broader range of sounds. Thanks just the same, don't suppose you'd know if it's practical to go about building your own parametric eq then? Or know any workarounds? This is good stuff! Thanks.
• 09-06-2003
RobR
This may be a good place to start.

Also I've always fancied the idea of building a bunch of stuff into a guitar. Triggering MIDI synths with a guitar sounds pretty interesting too.
• 09-06-2003
doubleanti
Excellent friend! That's a great and visual resource!

Yeah I was just looking at some schematics for wiring of volume/tone controls, and I was wondering well, how is there a different sound quality in volume and tone when you have just one type of circuit element, ie a potentiometer. Well, I would have thought about perhaps that hum canceling stuff about the phase differences in the voltage, and lo and behold after doing some node voltage analysis of phasor domain stuff, adjusting the 'volume' resistance does control the overall amplitude while the adjusting the 'tone' resistance changes the phase by increasing the imaginary part of the voltage, thus increasing the phase angle! Wow, this is so amazing!!! =)

Amen to Kirchoff... ::moment of silence:: =) Thanks!

PS! You realize that now I'm going to chang ethe expression I got for the transfer function so that I can get as close a 1-to-1 correlation between phase and rotation of my tone knob now, don't you? =) Oh joy the joy of electric circuits, even analog ones, wonderful!