CD4049 Revisited - i.e. Mark Hammer

[aron]

Mark,


I have revisited the CD4049UBE chip. I remember it having potential so I decided to wire up a Shaka front end to the CD4049UBE. I needed a tone control and I remembered your SWTC. While looking for it, I found Jack's SWTC2 which I wired up but did not have much success with it. Probably needed to change values. In any case, your original SWTC post mentioned using it in a 4049 circuit and yes, it works well.
I think the 4049 has so much potential. It distorts very smoothly, is easy to wire up (see comments later) and is controllable. It can get little to tons of overdrive and it sounds smooth!
While I am typing this, I realize that I could have made my perfboard wiring twice as easy if I had wired it from in to out following 7,6,5,4 pins.
Instead I did something dumb and wired it the opposite way OMG.
In any case, it is sounding very promising!!! Shaka 49!

[Marcos - Munky]

I'm curious on this one!

[rutabaga bob]

Yes!  Waiting for developments! 

[Mark Hammer]

Thousands of Red Llama owners/builders can't be wrong.

Don't forget to take a look at Stellan Lehrberg's "Slowfinger"; a "golden oldie"!   

[aron]

Just for reading, I found these older threads:
https://www.diystompboxes.com/smfforum/index.php?topic=17114.0
https://www.diystompboxes.com/smfforum/index.php?topic=59325.msg463297#msg463297
http://pedalprojects.blogspot.com/2013/04/how-does-red-llama-work.html

[aron]

After looking at the Llama and other schematics, I didn't even need the op amp front end. This chip has so much potential and I feel like we can use some of our tricks we have learned along the way to build nice circuits with this chip.

[Mark Hammer]

Personally, I like having an op-amp front end, because it provides opportunities for filtering/tone-shaping to extract a more pleasing overdrive from the inverters.   My personal bias is that I like to restrict the spectral input to something that is expected to generate harmonics, and then gradually spool out the resulting harmonic content.

I never did build Stellan's circuit.  But if I ever did, I think I'd stick a cap in the feedback loop of that op-amp.

[aron]

Have you tried comparing just using a single inverter as the first gain stage rather than op amp or transistor stage? I need to try and wire this up and hear what it sounds like. I was thinking one or two stages might make a nice little boost for a guitarist. It also might make a nice little treble booster.


I've been a bit bummed by our components going away like our J201 etc... but this chip is still widely available and could make a nice platform for a bunch of overdrive tones.

[11-90-an]

Sorry if kinda OT, but since you guys are talking about inverters, is there a formula for the gain of an inverter?

Somewhat like :  -(R2/R1) ?

[aron]

That is a good question. I don't know. I found this article but even this guy doesn't say:
https://www.parasitstudio.se/building-blog/cmos-workshop-part-1


I found this ... from this site:
https://www.diystompboxes.com/pedals/jo4049.html

[GFR]

Have you tried comparing just using a single inverter as the first gain stage rather than op amp or transistor stage? I need to try and wire this up and hear what it sounds like. I was thinking one or two stages might make a nice little boost for a guitarist. It also might make a nice little treble booster.


I've been a bit bummed by our components going away like our J201 etc... but this chip is still widely available and could make a nice platform for a bunch of overdrive tones.

Besides, with the opamp you can have a high input impedance, low output impedance stage before the CMOS stage, then you can use smaller resistors and more feedback to linearize the first CMOS stage, leaving gain to the opamp so that the CMOS stage can focus on just shaping the waveform. And with more feedback, it will add a smaller amount of distortion, letting you cascade several stages.

An output buffer could be useful too.

[GFR]

Sorry if kinda OT, but since you guys are talking about inverters, is there a formula for the gain of an inverter?

Somewhat like :  -(R2/R1) ?

Read this, it's a classic app note.
http://www.bitsavers.org/components/national/_appNotes/AN-0088.pdf

The open loop gain is about -30, so, if you're aiming for a much lower gain, yes, -R2/R1 is a good rule of thumb. As you get closer to -30, you get less than -R2/R1 (the maximum is -30).

https://wiki.analog.com/university/courses/electronics/electronics-lab-20?rev=1566561050

[anotherjim]

The gain can be Rf/Rin. I say can be...
An inverter has nothing like the inherent (open-loop) gain of an opamp.
There comes a point where the gain set by the resistors isn't available in the inverter.
It can end up with Rf only setting the auto midpoint bias. Rf can be 20M and still bias it. Rf is essential to bias it for audio.
Rin isn't essential. If it's a wire (zero ohm) and assuming the source has very low output impedance, the gain will be whatever the inverter open-loop gain is.
The open-loop gain is higher for lower supply voltage.
The inverter open-loop gain is not linear. As output swings to either supply rail, it falls - this is the compression effect.
Gain is maximum or = Rf/Rin at the zero-crossing. This means noise gets full gain while the full signal swing is compressed. At extremes when the inverter is forced to hard clip, this can sound very unpleasant IMHO.
The input impedance is only Rin when the inverter swing can obey the Rf/Rin ratio.
The 4049U, uniquely, doesn't have closely matched complementary P & N channel MOSFETs. This can create even-order harmonics. Using x2 inverters in series can add some odd-order harmonics.

[aron]

GFR and Jim, thanks for the info!
I just saw this in the application notes. I never realized you could do this and I haven't seen it on any overdrive pedals.
Seems like an easy way to cascade inverters. Need to try.

[marcelomd]

Another thing to try:

[aron]

I read that in the application notes. Parallel inverters for more current?

[marcelomd]

I've read somewhere it changes the tone somehow, but I don't remember the specifics. This configuration can supply more current, so maaaybe the inverters don't work as hard given the same load...

I don't have a lot of faith in it, but it's worth trying, if you are playing with one in the breadboard.

Me? I just like the fuzzy () feeling of fully using a chip. 14 pins are a lot for 2-4 transistors.

[aron]

I'm thinking a Vulcan front end to two parallel inverters 😁

[anotherjim]

I've never got the x3 inverters in series from the app note to work. I found all 3 needed their own feedback resistor in order to bias (can be really high >1M so as not to affect gain) and then the overall feedback resistor as per the note.
The app note is using the obsolete National 74C04 so that could be the difference, although I'm not sure what it is.

[aron]

No wonder we don't see it in reality. Did you try parallel inverters?