Need help with a circuit to separate frequencies before fuzz

[DaveM]

I'm working on a FF clone, and I want to use it for bass and guitar.  I'd like to have a crossover-sort-of-deal that separated some of the bass frequencies and only fuzzed the higher frequencies.  I don't want to cut the bass, I want it to pass by the fuzz circuit, unfuzzed. There's what I have so far. Is this what I'd have to do to split the audio, instead of combining it? It would only need two channels, and I'd put a HPF on one, and a LPF on the other? One channel going to the fuzz, and one to the bypass. I could use some dual-gang 50k pots to adjust both crossovers at the same time, and only have the volume adjustment on the bass portion.

Make sense?

Dave

[Gregory Kollins]

Check out the Gretch Contro-fuzz. This would be very similar in concept, with an extra trick. You would just have a tone stack on the clean signal and in front of the fuzz circuit. If you only want one tone setting (clean always the bass, fuzz always high end) you could do it with trimpots and have it all internal. However, if I was you, I would mount external tone pots for the clean signal and fuzz signal, that way you can mix and find a nice tone for the guitar and amp you're using.

Edit: I just took a look at the contro-fuzz schematic and it doesn't quite work how I thought it would. In fact I have no idea how it works. I know there are some people on here that do, though...

[DaveM]

I also found the Ibanez Phat-Hed, which seems to what I want my fuzz to do. http://www.youtube.com/watch?v=nR_6oM3ijFg  I'll have a look at the circuits and see if I can decipher anything.

[brett]

Hi
the Big Muff Pi has a tone section that neatly splits bass and treble with only a few components (and then mixes them with the tone pot).  If you replace the pot with a switch to divert one "side" or the other to the fuzz, you'll have it.
cheers

[Mark Hammer]

Actually, I'd avoid the strategy you are considering.  The Fuzz Face will need every last ounce of signal you can provide to get it to distort.  Cutting out the bass by means of frequency-splitting ahead of the FF will result in either a) much weaker distortion than you were aiming for (and possibly none at all) or b) a redesign of the FF to produce the intended buzz (in which case, is it a FF and why use it?).

Having said that, there is nothing wrong with taking the bass out of the FF output after distortion, and blending the result with a clean bottom.

[DaveM]

Mark Hammer:

So what you are saying is to split the output after the fuzz, cut the fuzzed bass, and mix it in with clean bass? So I'd just need a HPF after the fuzz, and a LPF on the clean lows, and a pot to mix them together.  I'd probably use a 50k pot followed by a 60k resistor and .01uF cap . That would give me a crossover swing of 114hz to 265hz, which I think is a pretty good compromise for guitar and bass. I'd put a mixer pot in between them, to adjust the amount of bass, because we all know that more control is better.

brett:

I had a look at the circuits you were talking about, or something similar here > http://www.muzique.com/lab/sat2.htm (second one from the bottom), I'd just remove the clipping diodes and put the fuzz circuit in between the 10k resistor and the mixing pot.  You think I could use a 50k pot instead of 100K? I have a bunch of them lying around.  Except with a 39k resistor and .01 uF cap, that gives a break frequency of 408.3 hz. (see above) Fine for guitar, but I'd want it lower for bass methinks.   But that circuit, as far as I can figure out, requires that I split the signal before distortion, which Mark Hammer isn't too fond of. Mind you, I place and equalizer before this pedal, so I can boost whatever signals are weak to get good distortion.

Is there a "better" option?

[brett]

Hi

You think I could use a 50k pot instead of 100K?

It would  certainly work with 50k.  But as you note (pun intended), the split in frequencies is too high.

That's where Duncan's Tone Stack Calculator saves the day [trumpet fanfare].
It lets you change any or all of the values, including the pot, to see what the effects will be.  It's a free and brilliant download.

Would a 150 Hz crossover work for you?  That would be a 10k resistor and 0.1uF cap on each "side" (one a LP and the other a HP).
Note that with this arrangement the input inpedance is lower than the standard BMP setup (larger resistor and smaller cap), so don't drive it direct from the pickups (unless thay are active).  However, any circuit will drive this ok.
cheers

[Mark Hammer]

Mark Hammer:

So what you are saying is to split the output after the fuzz, cut the fuzzed bass, and mix it in with clean bass? So I'd just need a HPF after the fuzz, and a LPF on the clean lows, and a pot to mix them together.  I'd probably use a 50k pot followed by a 60k resistor and .01uF cap . That would give me a crossover swing of 114hz to 265hz, which I think is a pretty good compromise for guitar and bass. I'd put a mixer pot in between them, to adjust the amount of bass, because we all know that more control is better.

Actually, what I'm thinking is that your input feedd the full bandwidth to the FF, and to a simple op-amp gain stage.  The op-amp stage has a cap in its feedback path to sufficiently roll off highs and mids (I'll let you pick the corner freq).  Bass level is set via the manner in which you adjust gain of that stage.

Meanwhile, the FF has several different output caps to select from, stock value and smaller.  If the bass path can be set to unity gain, then mixing it in with a stock FF sound should place it well in the background in most instances.  Rolling off the lows from the fuzz channel, and turning up the gain on the bass side should get you a "chestier" rather than "throatier" sound.

I suppose the trick is mixing them in a manner that is not so interactive that it sub-optimizes the FF output

[DaveM]

Mark Hammer
If we could avoid op-amps, that would be good.  I don't have any, but I've got transistors and caps and resistors coming out of my yin-yang.  So a simple pnp booster would be preferable to an op-amp.

brett
I always place a DOD fx-40B (equalizer pedal) pre-fuzz, so that should work fine. Would the bass be weak though, because it hasn't gone through the gain of the fuzz? I'm trying to figure out how you want the circuit to look here. So we are talking about this circuit,
 
placed at the input of my pedal, with the fuzz circuit replacing the clipping diodes and the 10k resistor, right?  Then we'd swap the pot for a 50k pot, up the cap by a factor of ten, lower the 39k resistor down to 10-12k.  So it would look like this:

[Mark Hammer]

This, my friend, is brilliant.  Damn, I wish I had thought of it!

You might wish to consider a cap between the distortion side of the 100k pot and the diodes, just to make the diode contribution to the mix primarily mids and highs.  But that's a smart circuit.  Hey, where IS Jack these days?

[Lurco]

This, my friend, is brilliant.  Damn, I wish I had thought of it!

You might wish to consider a cap between the distortion side of the 100k pot and the diodes, just to make the diode contribution to the mix primarily mids and highs.  But that's a smart circuit.  Hey, where IS Jack these days?

check the URL: http://www.muzique.com/images/sat11.gif  ! Jack`d 

[DaveM]

But I wanted to use the FF distortion, not diode clipping, so I used the circuit you just posted and moved some things around to make this, which I posted above.


The switch bypasses the crossover effect, for regular FF tone.

Is that going to work? 

[brett]

Hi
I'm not sure whether it will work like that.
A better otion might be to take the output from the wiper of the pot (no connection from switch to wiper) and feed the input to both the filter and the fuzzy goodness (in parallel).  That's INPUT->parallel filter and fuzz->mixer pot->output from wiper.  Then, an SPDT switch from input to output can bypass both the filter and fuzzy goodness.

If that's as clear as mud, please ask again.
I'm sure that this has many applications.
cheers

[DaveM]

Hi
I'm not sure whether it will work like that.
A better otion might be to take the output from the wiper of the pot (Which pot?) (no connection from switch to wiper) and feed the input to both the filter and the fuzzy goodness (in parallel).  That's INPUT->parallel filter and fuzz->mixer pot->output from wiper.  Then, an SPDT switch from input to output can bypass both the filter and fuzzy goodness. (I just want the switch to bypass the filter, so I can have fuzz with no filter)

So we're getting rid of the clipping diodes in this, right?  So I have the filter as is, sans didoes, and the fuzz in parallel, with a mixing pot connected to the outputs of each.  But that mixing pot would do what the 100k pot in Jack's circuit does now, so we wouldn't need that 100k pot. Which basically means we are just connecting a LPF and the fuzz in parallel, and mixing the outputs.  Right? If not, I'm lost and i need a schematic for this to click in my head. 

If that's as clear as mud, (it is) please ask again.
I'm sure that this has many applications.
cheers

[DaveM]

bump bump bump...

[owenjames]

All of these answers have been very complicated so far, if you want a simple mod just change that big 20uF cap to somethign smaller.

That cap is there to be a Zero resistance to AC signals while keeping the DC biased correctly with the 2K Pot.
When you twist the pot you are just adding more and more resistance to your AC signal, thus reducing the gain.
It is set at 20uF so that basically everything above 4Hz or so will have gain applied to it.
If you change that cap to something smaller, say 0.5uF, then this cuttoff changes (to 160Hz actually), so the gain the Fuzz knob gives will only be applied to frequencies above 160Hz.

I would try that first and see how it sounds, you might find that the bass is cut a little too much rather than just cleaned up, but for such a simple hack its worth trying before delving into a more complicated solution.

[DaveM]

All of these answers have been very complicated so far, if you want a simple mod just change that big 20uF cap to somethign smaller.

That cap is there to be a Zero resistance to AC signals while keeping the DC biased correctly with the 2K Pot.
When you twist the pot you are just adding more and more resistance to your AC signal, thus reducing the gain.
It is set at 20uF so that basically everything above 4Hz or so will have gain applied to it.
If you change that cap to something smaller, say 0.5uF, then this cuttoff changes (to 160Hz actually), so the gain the Fuzz knob gives will only be applied to frequencies above 160Hz.

I would try that first and see how it sounds, you might find that the bass is cut a little too much rather than just cleaned up, but for such a simple hack its worth trying before delving into a more complicated solution.

I'll try that.  I have a big pile of polarized caps kicking around, and if I like it I could have it switched, so that I could have full-range fuzz and only high-frequency fuzz available at the flick of a switch.  Or perhaps a DPTT switch for three options. I just happen to have one I salvaged from an answering machine. If it works, excellent idea. Thanks.

[DaveM]

owenjames, your simple solution worked quite well. By cutting the bass before it gets fuzzed, I could use the mixer at the end of the circuit to mix in some clean bass. Works excellent.  Thank you. So here is the final circuit I'm going with. Then I just have to finish putting it into an enclosure.