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I want to build an EQ (for acoustic guitar)

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DennisLeahy

New Member
Hello, first post here, and I am very much an electronics newbie.

I started designing and building acoustic guitars, and now want to add electronics. I would like to add a simple 4 or 5 band EQ to my current guitar (in the guitar, not an outboard module.) All of the commercially available drop in modules are big, ugly, clunky looking things that I would not want sticking out of the side of my guitar. 3-band EQ is not quite enough, as I want to have better control over the mids.

I don't need preamp capabilities - the pickup manufacturers offer preamps that are cheap and sound good, so I want to use those. I just want to add volume and EQ pots, probably small sliders. Again, just a newbie, but I'm looking at maybe using Bourns sliding potentiometers, audio taper. These will mount on the inside of the curved side of an acoustic guitar, so I will use short slider length. All I want sticking out of the guitar are the levers (coming through slits in the wood) for a relatively stealthy look compared to the plastic monstrosities availabee commercially.

So, now you know the scope of the project. And, I could really use some very basic help on designing the circuit. Since I'm such a newbie, I don't know but hope this can be done as a passive circuit, and still sound clean. I found a project for a 6-band EQ which is just slightly overkill for inside a guitar, and is active rather than passive, but maybe this could be adapted. I also may need to go with an active circuit to make a decent EQ.

I'll stop here, and ask if I'm in the right place, if I'm on track, and if anyone can help me with this (or just tell me to build the 6-band and be done with it.)

Thanks!

Dennis
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I don't know but hope this can be done as a passive circuit, and still sound clean. I found a project for a 6-band EQ which is just slightly overkill for inside a guitar, and is active rather than passive, but maybe this could be adapted. I also may need to go with an active circuit to make a decent EQ.
You need active, I doubt you're going to find a passive EQ - and if you did it would be rubbish.

Build the 6-band one!.
 

DennisLeahy

New Member
You need active, I doubt you're going to find a passive EQ - and if you did it would be rubbish.

Build the 6-band one!.
Thanks for the quick response, Nigel!

I will build the 6-band (which even gives info to make it a five band and provides a table of values to use for various Hz limit points.)

A couple of questions: that plan calls for linear pots. Doesn't audio taper make more sense for this project?

Secondly, any recommended specific brand and part number for the slider pots? I'd like them physically skinny so I can cram them together, clean sounding and reliable.

Thanks!

Dennis
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Thanks for the quick response, Nigel!

I will build the 6-band (which even gives info to make it a five band and provides a table of values to use for various Hz limit points.)

A couple of questions: that plan calls for linear pots. Doesn't audio taper make more sense for this project?
Not for active tone controls, they should be linear.

Secondly, any recommended specific brand and part number for the slider pots? I'd like them physically skinny so I can cram them together, clean sounding and reliable.
I've not had to source any for years, but it's a question of finding some that are the size you want - you may not have much choice over their quality.
 

DennisLeahy

New Member
Now I'm really going to show how much of a newbie I am with electronics components and circuits...

The physical limitation of size for the pots to be mounted on the curved inner surface of an acoustic guitar side (with just the arm of a slider or the tip of a thumbwheel erupting through the guitar side, to be accessed from the exterior), makes slide potentiometers too long, so I'm down to thumbwheel pots.

There are the cermet trimmer style with a very low duty-cycle (like 200 cycles) that were obviously not intended as user controls, and heavy-duty cycle (like 10,000 cycles) thumbwheel potentiometers. Unfortunately, the thumbwheel pots that I can find at 5K Ohms do not get up to .25Watts (which is the minimum wattage for that EQ project plan I linked to in the first post.

The closest I could find in thumbwheel pots at 5K is .1Watt: Xicon 311-1700-5K

So, my stupid question is what happens when using pots with a lower rated wattage? (.1 instead of .25) Will they fry, or will they be noisy, or will they break-up as the pot approaches maximum?

I have to assume that the EQ circuit I linked to is for a preamp signal (which is what I will have) and not a signal that has gone through a main audio amplifier. But I guess I am surprised, because I would expect the preamp signal to be just milliwatts, and hope that the person who designed that circuit went into heavy overkill on that .25Watt spec.

Any thoughts?

Thanks,

Dennis
 
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