Frequency filters for guitars

[Shockwave]

Do you mean a tone control? A capacitor and potentiometer in series wired from signal to ground acts as a variable 1st order low pass filter. If you want a real variable frequency, variable slope active low pass filter, you'll have to either get a voltage controlled filter module from an analog synthesizer, or an electronic speaker crossover.

-Eric

[ThomasDodd]

If you want a real variable frequency, variable slope active low pass filter, you'll have to either get a voltage controlled filter module from an analog synthesizer, or an electronic speaker crossover.

I didn't see him mention variable. I was thinking speaker crossover too.
Theere are site to help you calculate the caps and resistors for th desired frequency for different types of filters too. 3dB/octave would proobably be enough, but you could get better if you spent the money.

Not sure any will fit in the guitar though. For that you'd probably need a full active filter.

Maybe one of these?
http://www.discovercircuits.com/PDF-FILES/lowpass.pdf

This would help some too, particurally if you want to change the cutoff.
http://alpha.science.unitn.it/~bassi/Si ... loa049.pdf

[adam0408]

Let me get this straight: You want something that sounds really funky, right... not just a glorified tone control? If you are looking for a new sound on your bass, may I suggest adding active electronics. There are many companies that offer parts for this and you could probably do it for $300 or cheaper. http://www.carvin.com

your problem with fitting extra electronics in a bass will come when you discover you dont have enough room in the control cavity. My guess is that this will definately be the case. Wait, I am not guessing, I know. What you will no doubt have to do: fit a stompbox worth of electronics in the back of your bass, (unless youre some sort of electronics whiz and design your own miniature electronics) drill several holes for controls and fit a 9v battery in there. What this means is probably a new 4"*4" hole in the back of your bass. Not worth it the way I see it. You can get a pedal that does just as nicely, and doesnt cause permanent damage to the bass.

Also, I dont really understand what use you would have for a low pass filter. (unless as a special effect) What this will no doubt do to your sound is make it undefined and muddy, unless used very sparingly, and to which I say, why not go for active electronics?

Here is a pedal that seems that it will do all that you require, for $265 http://www.musiciansfriend.com/srs7/fg= ... id/158330/

My advice to you is to get the pedal.... this means if you tire of it, you can sell it off (or return it immediately) instead of investing time and such into a massacre of your bass. UNLESS.... you fabricate your own pedal and do it cheaper... thats the only way I would agree to such a scheme as this.

[ThomasDodd]

The second-order low-pass filters described in the TI article are probably closer to what I'm after, but could you fit the result in a guitar? This may be a somewhat more complex idea than I originally thought.

Most active filters can be small. The opamp is the primary part, and not large. If you put it on a PCB it'll take a lot of space, but you don't have too. You do the rat's -nest kind of thing, using short leads and wire. Onec it works, you cne wrape it up pretty tight with electrical tape, testing as you go of course so when you break something you can easily fix it:)
You can always pull the "tone" control to make some room:) Power could be tricky and might take some inventive design. Maybe a lithium battery, smll camera batteries, or the button shapped watch/calculator batteries.

As long as you want a fixed cut-off, it not bad. Variable gets tricky.

Remember this is low power, so you don't need the big caps and coils like crossovers use.

Send me the frequency, and I can help you find parts. You can probably get most of them from RadioShack, evn with the crappy selection they have these days.

[ThomasDodd]

This approach seems superior, but it's a good question if I could get it to work as a homebuild. My dad has electronics knowledge, and I have some basic knowledge, but this looks more complex than I originally thought. I'm not trying to integrate an effects pedal into my bass, and I know I have the room for something like this. If it was cheaper than $700 to build a variable version of one of these, I'd be glad to try.

OK. You replace the tone control with sutible pot for the filter. Looks like that are replacing the "volume" control with their own gain controll too. It'll be hard to match th surface mount PCB they attace to he pot, but you can get pretty small. They also replace the phono jack with somethingf that'll switch power to the filter. I did this somwhere before, but don't remember the part, I could find it though.

You still need to decide on a cut-off frequency (or range) to design the filter. Then look for an online filter designer to get the corect caps and resistors. I'm sure you can do it, at least with a little help

[ThomasDodd]

Alembic makes all of their electronics and most of their hardware in-house, so it would be hard to duplicate. How would I go about deciding upon a cutoff frequency? I'm assuming that this goes beyond the normal 250K/500K that most pots follow.

You might ask Alembic? Otherwise, trial and error. You could try recording with out the tome control to get the normal response of the pickups. Then use digital filtering tools, to find the frequency and roll-off rate you want (3db/octave?, 6dB? 12dB?)

The old school way would be several, big analog passive filters, and just play with it untill you like the sound. Then develop the active filter and minitureize it.

Once you found the sound you want then you can design the filter

The range on the pot really depends on the frequency range, and the filter design. You might need a smaller range on the pot, or maybe a multi turn pot.

[ThomasDodd]

I know that it's been a while, but here's what I want to build: a filter with a cutoff frequency of 350hz-6kHz and a slope(rolloff) of 12dB/octave. I finally found the info. So where can I start?

This Is probably the easiest.

I'll have to do some looking to figure out the 350-6k variable thig. 6k seams high fo a low pass filter though. I was expecting about 100-400 Hz.

[Tom Mason]

I'm not trying to ask the wrong question, but would your situation be helped by using a graphic equalizer that has a low pass built in as well as the usual adjustment in the range you desire?

I'm thinking about a 2/3 octave mono equalizer, and I'm thinking that I've seen an Alexis that has a low pass cut as well as a high pass. When I'm at church tomorrow, I will see what brand our system uses. It is new, and it is the one I'm considering in this application.

Tom Mason

[ThomasDodd]

I'm not trying to ask the wrong question, but would your situation be helped by using a graphic equalizer that has a low pass built in as well as the usual adjustment in the range you desire?

Never seen an EQ that would fit in an electric bass/guitar.

[Tom Mason]

I'm talking about chaining it into the system. If he is sold on having something built into the body of his instrument, then no.

I am looking at this from the perspective that I would personally not want to reconfigure the instrument if possible. That, of course is his decision.

Tom Mason