Looking for help to Mod Anderton's quadrafuzz

[Shaukou]

Hello,

Rescently i've become unsatified of my distortion pedals and the idea to make my own pedal crossed my mind. I've got a small idea of what i want to create but don't have the knowlege to manage the design part. That's why i'm looking for someone willing to take part in that project with me.

That said, here's the think i've been thinking about:
I would like to have a pedal that allows me to modulate the distorions of specific frequences. The goal being, for exemple, to have a strong distortion on low frequences and clean high frequences on the same time or the opposite.

So i thought about doing something like:
1- amplifying the input signal with a pre-gain
2- Splitting the amplifyed signal into 2 or 3 signals of specific frequences through (parametric?) filters
3- having a number of distortion circuit equal to the number of splited signals with independent controls
4- Gather the splitted signals and sending it to the output.

The pre gain and splitting sections could also be 2 or 3 boosts on specific freq bands.
The distortions circuits could be differents depending on the wavelength targeted.
The pedal would be designed for bass guitar.


Now that i exposed the project, if somebody is interested by this project i would gladly accept some help to design the circuit.
Thanks,
Shaukou

[Resynthesis]

Have a look at the Quadrafuzz

[R.G.]

Yep. Craig Anderton's Quadrafuzz does almost exactly what you describe.

[Shaukou]

Hi,

After a small look at it, it seems that the quadrafuzz is realy near what i'm loocking for. But unless i missunderstood the schematics, it seem that the distortion setting is pre-set and you can't tweek it. So yes, it's near what i'm looking for but i want to be able to modulate the distortion/fuzz of each band separately.

So basically, i would have to replace the 4 distortion parts of the circuit for others distertions circuit including the knob i'm loocking for. Is that it?

Here is the schematic from PAiA: http://www.paia.com/ProdArticles/quadrafz-design.htm

If i take the upper branch of the circuit for exemple, do i replace everything from R8 included to C24 included by the new distortion circuit?

Thanks for the answers,
Shaukou

[R.G.]

As shown, the amount of distortion in each band is semi-fixed, depending on the setting of the attack control.

The attack control increases the signal level sent to all of the bandpass and fuzz circuits. Increasing the attack level increases all of the distortion "drives" at the same time.

The output of all four distortion circuits is individually adjustable, letting you reduce that distortion band's amount in the final mix.

You can change the amount of distortion (as opposed to how much of that distortion appears in the final mix) in each band by one of two ways. One is to install an input level control per band, either before or after the bandpass filter. This cuts the distortion in that band by decreasing the signal level into the distortion. The second is to make the 100K feedback resistor be a pot in series with a resistor on each distortion circuit. This changes what most people would think of as the "drive" setting of the distortion band individually.

Of course, you are also free to change out the distortion circuits, one or all of them. Another option is to add a control to blend in some dry signal to the final output even when distortion is on. This would have the effect of leaving some of the original signal in a band where the fuzz was fully down, doing much of what you're describing a different way.

The Quadrafuzz is remarkably flexible as it is. It may already do what you want well enough. It might be best to build a prototype of the Quadrafuzz and experiment with it first before going off and adding another four controls. There is serious danger of making something with too many knobs to be useful.

[Shaukou]

Thank you R.G. for your answer.

Adding a blend pot into each band is an option i thought about at first and it's a part i wanted to include in the circuit.
As you said, i'll probably build the circuit as is and try some modifications, making sure to keep the differents fuctions on differents PCBs to keep the modifications as easy as possible.

The effect loop doesn't interest me, so can i remove this part of the circuit without any other changes?

Also, do you know if anybody has ever listed the components for this circuit? It seems all the informations aren't shown in the schem.
PAiA sells a kit for 85$. Do you think it would be cheaper to buy the components separately?

[R.G.]

The effect loop doesn't interest me, so can i remove this part of the circuit without any other changes?

Yes. You must keep the mixer part of the loop circuit, but the amplifier section after that is not needed.

Also, do you know if anybody has ever listed the components for this circuit? It seems all the informations aren't shown in the schem.

See: http://www.synthmanuals.com/manuals/paia/6720_quadrafuzz/assembly_and_using_manual/6720k_quadrafuzz_200dpi.pdf

PAiA sells a kit for 85$. Do you think it would be cheaper to buy the components separately?

Maybe. PAIA kits are not terribly expensive for what they are. However, the kit includes a rack panel and many jacks and other things you may not need, as well as a PCB that you may or may not use in the end.

However, the cost of parts is not generally a good guide for whether to go one way or another in an experimental effect design. In my first version of the Guitar Effects FAQ back at the dawn of the internet, I posted something that I think is still true today. The majority of the cost of any effects pedal is not the electronic parts. It's the enclosure, switches, control pots, knobs, and the mechanical parts that matter most. Resistors, capacitors, transistors and ICs have continued to get cheaper and cheaper, which the cost of a pot, knob or switch has not declined much. And enclosures can be really expensive if you want good looks, or really cheap if you are willing to settle for something that looks knocked-together.

To a first approximation, you can consider the actual parts on a PCB to be free and add up the cost of the enclosure, knobs, switches, pots and so on and have a good guess of the cost of the pedal if you build it. Because you are experimenting, you will also necessarily spend some money in trying things that don't work in the end.

[jimbeaux]

You can find a pdf with the Quadrafuzz schematic, pcb layout & parts list here (last page) > http://paia.com/talk/viewtopic.php?f=6&t=89

One concern is that the RC4136 used in the PAIA kit is now obsolete (3 required) - they're not hard to find - but cost a little more, If you're experimenting or doing a new design - a good choice would be the TL074 - much cheaper (about 50 cents ea) - but unfortunately they are not pin compatible with the RC4136.

I built the PAIA project & it works great - much different than conventional distortions - I added the separate output jacks for each fuzz channel & ran the lo & mid 2 to one amp & the mid 1 & treble to another amp - the un-modulated "stereo image" is interesting - and different.

I have an old Craig Anderton article (before he did the Quadrafuzz) - He discusses different ideas on experimenting with pre-filtering / multi-fuzz - one is really simple - it's a block diagram (not schematic) using the state variable filter (SVF) from EPFM & feeding the hi-mid-lo outputs to three separate distortion circuits (your choice - identical or different) and feeding the outputs to a simple mixer. Using the SVF would allow you to change lo-mid-hi frequencies simultaneously & also change resonance too.

Using different one and two stage fuzz circuits - input/output phase could become an issue - If it sounds thin - could be phase cancellation.

If you're interested in the Anderton experiment article - just let me know - I can e-mail it to you.

[Mark Hammer]

Here is a reduced version of the Quadrafuzz I editted down from the original.  It is missing the highest frequency band, the filter, and the electronic switching.  But, it provides for 3 bands, the splitter and mixer stage, and only requires two quad op-amps.

I have always been of the view that, as forward-thinking as the overall design was, applying the same gain to frequency-bands thathave different intrinsic amplitude levels was a little short-sighted.  Consider making R39 a little larger in value than R40, and R38 a little larger than R39; e.g., R40=100k, R39=150k, R38=200k

[Shaukou]

Thanks for all the answers. I'm curently trying to recreate the schem to make my own pcb and in the same time looking for aviability of every components and i've got a question about a capacitor.
12 4.7uF 10v capacitors are requiered and le listing says electrolytic capacitor but i can't find a matching capacitor of this kind. I instead found this one: https://www.banzaimusic.com/Tantalum-4-7uF-10V.html

Would it be ok to use this one instead?

Just found after some researches that tantalum capacitors are in fact electrolytic capacitors too.

[jimbeaux]

This should work > http://www.banzaimusic.com/4-7uF-50V-Radial.html

You're going to power it with a bipolar power supply (from +/-9 to +/-15 vdc) & on-board regulators (7805 / 7905) are going to take it down to +/- 5 volts > 10 volt capacitor rating is minimum - My kit came with 4.7 uF / 16 v electrolytics - the ones above are 50 v & should work just fine. I don't see anything in that value below 50 volt rating (at Banzai) - there are some 25 volt ratings but they are non-polarized.

[armdnrdy]

Mark,

Did you remove the highest frequency band because you felt it wasn't audibly useful...or just to reduce the size of the circuit even more?

[Mark Hammer]

Both, but also because if I removed the LP filter, best not to have too much uncontrolled buzz.

[armdnrdy]

Gotcha!

Thanks Mark.

[armdnrdy]

I have to admit...when I first read Shaukou's first post..I was caught between  and 

But after the inclusion of the Quadrafuzz, MH's, and R.G.'s modifications and suggestions into this thread...I can see where the Quadrafuzz circuit can be made into something very interesting and useful.

I like the idea of a separate controls (gain adjustment, tone) for each frequency band.

This would be like recording the exact guitar parts with different amounts of fuzz, EQing them differently, and then adjusting the level of each track with the mixing board faders to your liking.

[Mark Hammer]

As much as I like to tweak stuff, having individual gain controls for each band starts to get too complicated.  I prefer having a single master drive control, and simply mixing the bands down.  That doesn't preclude use of trimpots inside to set the drive of each channel appropriately, but the ability to futz around with individual drive controls on the panel just invites one to get lost in tweaking and forget about playing.  Besides, the filter bands aren't that sharply divided anyway, so you'd be driving yourself crazy about things that end up not making a lot of difference.

If it was only two bands, then separate drive pots might be useful.  I whipped up a simple overdrive several years ago where I had individual clipping stages for the high and low range, with a couple poles of HP and LP filtering to split the signal.  A simple blend pot, akin to the balance control on a stereo, let me mix the proportions of each channel.  I only used a single gain pot: a linear pot wired up as the ground leg for each of two non-inverting stages, in reciprocal fashion.  That is, increase the gain for one side and you decrease it for the other.  Three controls - gain/antigain, balance/mix, and output level - gave a fairly broad range of sounds.  If I had it to do all over, I think I'd knuckle under and use 4 pots: gain-Hi, gain-Lo, blend, output.  But that's as complex as I'd have patience for.  YMMV

[Processaurus]

Just eyeballing the design, I wonder if it will have an overabundance of high frequencies, because, even the low frequency band will be producing a fuzz with abundant highs, because the distortion generates artificial harmonics above what is being fed into it.  Like how you can get a full, synthy fuzz with a normal fuzz pedal with your neck pickup and the tone knob down, if there is enough gain.  I'd bet the same thing is happening here, all of the frequency bands are generating high frequencies with their fuzz section, and these get added together.

Might be worthwhile to put a tone control on the end, after C21, like Mark's Stupidly Wonderful Tone Control.  Changing R2 (in the feedback loop of IC1A) to 10K would add some extra gain that the tone control eats up.

[armdnrdy]

There is a tone control on the original.

The dual 100K.

[Ben N]

I always thought a hex-inverter based Quadrafuzz might be interesting.

[deafbutpicky]

It is, search for Thrice I here.
Only down side is phase cancellation when you start messing with different distortions
per band. I thought about adding phaseshift stages but they need to be readjusted
with every change...