Isolating Bass Freq Range?

[petemoore]

What I would like to build is something that would provide a narrowed bass frequency range, and rolloff everything else.
  Something  I could use to tune where the low end frequencies beging their attenuation.
 High and mid rolloff could be obtained with a 'sharp enough' cutoff using sipmle rolloff cap circuit?
 Any advice on how to get a tunable narrowed bass frequency 'passer'?

[niftydog]

can't give you any specifics, I havn't ventured down this path yet.

But I can suggest that you google up some "active bandpass filters" and see what you get!

[spongebob]

I recently found this PDF on the TI website:

A Single-Supply Op-Amp Circuit Collection
http://focus.ti.com/lit/an/sloa058/sloa058.pdf

Chapter 3 is the most interesting, it deals with active filters and also has the formulas to calculate the needed resistor/cap values. There are multiple different bandpass and lowpass filters in it, some stuff looks really scary though, but most of it is pretty straightforward.

[petemoore]

Are these like ratio codes?
 C1=10C  [means that capacitor should be ten times the size of one labeled 'C' ?
 
 R1=10R
 R2=.001 [can you tell me what you see in these equations, I would end up socket/potting everything [which isn't that bad], if I could de-code or read technical texts like these, or if I had an example with 'the answers' one time, I might improve my comprehension...I wish I could read better...!
 Someday, hopefully soon this part too will make sense, at this point I'd be guessing values, which might not be that bad, somebody figured it out once...
 I'm PDG at looking at schematics with values, and being able to predict in many cases how changing the value of a given part will affect the circuit. I just wish I could read tech. text better.

[Greg Moss]

I just found this site with useful looking crcuits, and clear explainations....
//http://sound.westhost.com/dwopa.htm

Greg

[petemoore]

I tried pasting in the window a couple of times..

[niftydog]

http://sound.westhost.com/dwopa.htm

[downweverything]

Are you asking about like a filter that only passes low frequencies and has a steep cutoff?     you can just cascade RC filters till you get the cutoff you want if thats even what you were asking...

[brett]

High Pete.
Try this.
Take 4 10k resistors and line them up (serial).  Input is on your left, output on your right.  Connect 4  0.047uF caps from the rhs of each resistor to ground.  

That filter will more-or-less split your guitar down the middle.  For a lower freq split, increase the caps or raise the resistors, and vice versa ofr a higher freq split.

cheers

PS you might need a buffer before or after this setup to minimise unwanted signal losses.

[spongebob]

Are these like ratio codes?
C1=10C  [means that capacitor should be ten times the size of one labeled 'C' ?

Yes. Finding the correct values can be tricky, especially for the more complex (but also more efficient) filters, so here's an example (from page 17):

Unity Gain Butterworth Low Pass Filter:

F  = 1 / (2 * Pi * R * C)
R1 = R2 = R / squareroot(2)
R3 = R / (2 * squareroot(2))
C1 = C
C2 = 4C

F is the corner frequency of the filter and depends on the values of R and C, you can choose either R or C and calculate the other value, let's say we choose C and calculate R:

R = 1 / ( 2 * Pi * C * F) or in a more convenient form:

R [kΩ] = 1000 / (6.28 * C [nF] * F [kHz])

now if you have a 10nF cap and want a corner frequency of 2 kHz you will get R = 1000 / (6.28 * 10 * 2) = 7.96 kΩ, let's say 8K

R1 and R2 would be 8K / 1.41 = 5.6K
R3 would be 8K / 2.82 = 2.8K
C1 = C
C2 = 4C = 40nF

Hope this helps!

[petemoore]

Everyone and Brett, I'll try that seriesed R's with caps to ground where they meet...[right?]...what is 'rhs'? ...this is a way to get a sharp cutoff frequency for treble rolloff?
 The original  :idea:  is: islolate bass [extensive experimentation may be necessary] so that there's a prominent ^ somewhere in the 'bottom end'.
 Ok so say I've got the bass isolated, then I treat that much differently [no reverb, different processing..say Comp/EQ.
 ...The 'other side' would be full range [maybe some bass rolloff] and would get treated much like 'normal' say through a DIST device, reverb, echo, phase...whatever I would 'normally' do with a full range signal.
 Then Mix the two separate chains back together with a mixer, or just a pot...I've seen both ways...[], what would you recommend for a way to mix the side chain [the separated separately processed bass] back in?
 I figure the best way to learn to swim is just jump in the water, but practiceing a few 'strokes' before jumping isn't a bad idea...
 I have a trouble getting great bass definition, and reverbing etc. seems to turn bass to mush, as does other types of processing...basically I want mostly clean compressed bass tones, mixed with distorted, reverbed etc. full range [with a bit of bass rolloff since that's being taken care of separately then mixed back in].
 My ideal bass range peak device[that's what I'm thinkin of leaning toward is just a prominent peak of bass frequency band] could 'slide' it's boosted frequency band up and down, and the width of the band couuld be altered also. I don't think ultra sharp cutoffs of lows and highs [I think cutoff around low mids at the top of the peak scale] would be necessary.
 I appreciate all the help, I'm trying to form applicable questions and theory...having maybe some troubles with nomenclature [words]...
 I think what I want is this: a Med. width, fairly strong, Low frequency peak...a low freq band pass filter, something that would attenuate ultra lows, and high end starting around low mids...leaving a fairly narrow bass frequency signal...
 Actually I don't really know what I want, I've never seen this done, just seems, in theory at least, that treating bass range differently could have benefits...

[RDV]

What I like most about my little pedal development is that the bass notes aren't mushy at all, in fact last night(much to my wife & children's chagrin) I AB'ed my HMP with every distortion I've got, and without a doubt, other than my SD-1/808, it had a clearer bass response than anything I've got, and the SD-1 can't touch the amount of distortion of the HMP. Mushing out bass notes seems to be a component of any high-gain pedal IMO, unless you do something about it EQ-wise.

RDV

[petemoore]

I must fine tune the HMP, and box it in it's entirety [including the 'Heavy' section/PEQ], then give a Good test run through the big amp...just got the First OA's 1a and 1b and clipping sections built and 'lit' last night...sounds PDG in the initial testing.
 Very heavy distortions available, and nice OD tones too. !!! Lotsa places for mods and tweex.

[RDV]

If one wanted to. One could put an external knob for all the trims & or fixed resistors in the HMP for a total of 8 freaking knobs man. Troubledtom would be proud! :wink:

You'd have:
1. OA 1a Gain
2. OA 1b Gain
3. Diode clipping warp
4. Treble roll-off
5. Bass Resonance
6. Bass Cut/Boost
7. Bass Frequency adjust
8. Volume

Howza!

RDV