cd4069's good for fuzz?

[pinkjimiphoton]

yah, it's a cool sounding kind of fuzz, very different from most of the other methods of getting it.
petey two finger turned me on to a lot of ideas for further exploration.

this thing isn't a sound i normally use, myself, it's too "metal" for my taste. i have a few friends tho that are in love with that.

thanks for the link mark, and the advice... as always, i'm standing on the shoulders of giants.

i worked up a schematic (with apologies to justin philpott, who's schematic i appropriated) for you guys.
the tone stack section i don't think is something i've seen before. have you?
what the hell am i doing, and why does it work? is it some kind of feedback network or something?
beats the hell out of me.. but it's gonna lead to , and merit further exploration i guess.

here ya go.. the boogie snake:

[petey twofinger]

ot , but i cant stop thinking of jimmy tango now ...

[pinkjimiphoton]

ok, i'll bite.
who?

[jonasx26]

the tone stack section i don't think is something i've seen before. have you?
what the hell am i doing, and why does it work? is it some kind of feedback network or something?

No, never seen that before.. You usually want to have the inverters share the work 
Lots of circuits use paralleled inverters to get higher output current drive, CMOS-inverter headphone amps comes to mind.

But I think your circuit does the opposite.. With the tone-knob set to the least amount of treble-cut, the inverters share the 'work' about equally.
At max treble-cut the inverters become unbalanced, with the top inverter doing most of the work..
Not entirely sure though.. Sure is a strange circuit. And I haven't had my coffee yet.

[pinkjimiphoton]

thanks for the explanation, jonas.

i for-sure don't know what i'm doing, but it does seem to work well. i was thinking maybe it was some kinda phase cancellation or something.
sure would love to know what i did, and how it works.

[Mark Hammer]

One of the things I've tinkered with is using a treble bypass cap on the input to the first invertor so that upper mids have less attenuation applied to them before hitting the first invertor stage.  Under medium-to-low gain conditions, with juuussst the right amount of treble-rounding on the output, you get a wonderful Rick-into-Vox bite...at least to these ears.

I use a voltage-divider arrangement between op-amp input stage and invertors, but in your case, somethng like a 22k resistor in series with a 4n7 cap, and placed in parallel with the 68k input resistor might be the ticket when you want to brighten things up a bit.

[earthtonesaudio]

Re: the tone stack,

One "feature" of CMOS inverters when used as linear amplifiers is their high output impedance.  This is not listed in the datasheet.   Think of each inverter as having a built-in resistor in series with its output.  This is what lets you parallel them and also lets you get away with capacitively coupling stages (both of these practices would be unstable or smoke-releasing if used with op-amps, for example).

Since the output of your RC tone filter is taken from the pot's wiper, you have two things going on:

Part 1: Inverter B sees a variable resistance + cap to ground.  This type of tone stack is seen in many single-transistor boost circuits.  Move the wiper toward the cap, the output is loaded down with more capacitance.
Part 2: Inverter C sees a more constant RC load, but the tone pot is wired as a voltage divider.

To the extent that this circuit is a linear system, the superposition principle applies and we can just add the effects of Part 1 and Part 2 to see what happens.

[pinkjimiphoton]

ok, one more time in english?


thanks alex, and mark.

this is just the first experiment.. and i LIKE it a lot!!
but i have several of these chips, so i'm gonna see what else i can find to work with.
petey was kind enough to send me this, many ideas for mods:



be curious to see what happens. definitely gonna mess with the basic circuit some, thinking the unused stages may come in very handy with this kind of tone control..
i'm imagining there's a lot that can be done.

i got some weird sounds out of this too, with diode clippers of different kinds in different places...octave downs, weird tremolo and modulations etc...

almost thinking i could add a simple phaser/wobbletron kinda circuit to it. this is fun,
i'm actually learning about this stuff now instead of just copying everything.. a lot of epiphanies lately!!

thanks for the advice, help, and support.

i still don't understand the tone stack thing...i may be too stupid to explain it to! 

mark, i'm gonna try that treble bypass cap idea... i bet it will tame it down just enough.
right now, it's a little too "metal" for me still.

i called it the boogie snake, cuz at some settings it sounds vaguely boogie-ish... and then tube steak boogie popped into mind, and well,
i liked the way boogie snake sounded. it boogies, and it's got some TEETH. and it's fairly "slick"...so...

i know, i know... mama dropped me on my head too much. lol

[petey twofinger]

jimmy tango :

http://vimeo.com/28408779

[pinkjimiphoton]

oh, THAT!!

[jonasx26]

Re: the tone stack, ..

Yes, you're absolutely right. But I'm not at all sure as to what extent the system can be considered linear 
I'm thinking that the high (and varying..) output-Z makes stuff interact a lot.. Not sure though.

[samhay]

Cool thread - have some 4069s in my stash and am now feeling like I need to abuse some of them. If we keep the gain down, it seems they could make a cool cabinet sim.

What is the input and output impedance of each inverter?

Edit: I guess the input impedance into the inverter will be very high (it's a mosfet after all), so the input impedance will usually be approx the parallel resistor. The output impedance seems to be a bit trickier, but I'm guessing low-mid k-ohm if we can directly couple stages?

Is there any harm, as a first approximation, in treating each stage as an inverting op-amp with an output resistor?

[digi2t]

Is it my imagination, but shouldn't any unused CMOS inputs be tied either high or low?

To quote PRR from my DOF build;

> it states to ground any unused inputs in the 4049.

It should say: do SOMEthing SOLID with un-used inputs. They are like dogs. If you let them wander around loose, they WILL get into trouble. In CMOS, they may howl supersonically, or they may wander to a middle voltage and run hot. In digital logic, such things can lead to unexpected logic; in audio maybe strange noises and maybe nothing bad.

Jam them high or low, whichever is more convenient; makes no difference.

Whether inverting or not makes no difference: just get them to one extreme or the other so they "stay".

[jonasx26]

Is there any harm, as a first approximation, in treating each stage as an inverting op-amp with an output resistor?

No harm. Inverting amp with very low open loop gain.

[samhay]

Is there any harm, as a first approximation, in treating each stage as an inverting op-amp with an output resistor?

No harm. Inverting amp with very low open loop gain.

Thanks Jonas.

[pinkjimiphoton]

as usual, i'm a hack, so no idea why or how something works.
it either makes a cool noise, or it starts to smoke, ya know?   

[samhay]

No worries Jimi, and sorry for the slight hijack - I think that is a very reasonable approach, and you do seem to make a lot of stuff that makes a cool noise. I guess we don't get to hear about the smoke, but I am also guessing you get much more of the noise than the smoke these days?

[pinkjimiphoton]

thanks sam...

yah, more function than smoke these days, thankfully. i DID melt some NPN's the other nite tho, trying to get a dual led flasher circuit going. trying to create a "tremolo" to kinda mimic the old phase split fender harmonic vibe of the yellow and brown amps.

it's stupidly hard to get too led's to flash perfectly 180 degrees out of phase, AND be able to control the speed.

dino,
beat me bro. i DO know that

[samhay]

it's stupidly hard to get too led's to flash perfectly 180 degrees out of phase, AND be able to control the speed.

Did you figure this out? If not, take your op-amp LFO of choice and couple it, via a 100R-1k resistor, to the (-) input of an op-amp with anti-parallel LEDs in the feedback loop. This is how my 'another optical compressor' works. I can knock up a schematic if you like, but I fear I will derail this thread completely.

[pinkjimiphoton]

i'd love to see your schematic, sam.

i'm one of them guys who just don't "get it". i'm a hack, and lucky. fuzzes are easy. all ya need is patience and the willingness to waste components.
eventually, you make it work.