Fuzz Pedal Oscillation issues

[FSFX]

And off topic of the original post. But thanks for sharing.

For your future reference,  I give you a circuit from the 1959 4th edition of the GE Transistor Manual to consider.

[johngreene]

And off topic of the original post. But thanks for sharing.

For your future reference,  I give you a circuit from the 1959 4th edition of the GE Transistor Manual to consider.

Ah, I guess you got me because nothing has been learned since 1959. Just look at how they did the +ve supply rail in that circuit.
Think about it this way: you are bypassing the emitter resistor with that capacitor (with a variable amount of series resistance) so the "best" place to connect it is across the resistor it is bypassing! By returning that cap to the ground, it will tend to couple in everything "else" that resides between the + and - supply. As battery impedance increases your gain will go down, as an example. Unless you use very low ESR power supply caps and a lot of them.

[FSFX]

. . . . . because nothing has been learned since 1959

Exactly- you got that right. Just look at all of the pedal designs out there and you will see that no progress has been made at all by those in the DIY pedal community.

Those designs were done by real electronics engineers who understood their subject matter.

[johngreene]

. . . . . because nothing has been learned since 1959

Exactly- you got that right. Just look at all of the pedal designs out there and you will see that no progress has been made at all by those in the DIY pedal community.

Those designs were done by real electronics engineers who understood their subject matter.

Or......
They had nothing better at their disposal. 🤔

[PRR]

> Think about it this way: you are bypassing the emitter resistor

In the larger picture: you don't bypass a single part, you close the loop as direct as possible.

In any case, being abrasive is not helping.

[johngreene]

> Think about it this way: you are bypassing the emitter resistor

In the larger picture: you don't bypass a single part, you close the loop as direct as possible.

In any case, being abrasive is not helping.

I can't seem to not come across that way when I write. It's been an issue with me since the USENET days back in the 80's. It always sounds less abrasive in my head.

And I am not sure I agree with you entirely. When bypassing the emitter you are setting the RC time constant and the only way to at least control how those two comments interact, is to connect them to the same points. In my humble opinion.

Anyway, I probably should refrain from posting until after my surgery so I can sit at my computer and provide examples of what I am saying rather than trying to explain it in text since writing is not my strong point. All I really wanted to do was give my experience with oscillation problems in this style circuit to help out the OP.

[FSFX]

In any case, being abrasive is not helping.

John thinks he knows everything and the rest of us know nothing. He has no respect for anyone else, even those who have worked in electronic design for the last 50 years or more.

I see no point arguing or engaging in this forum anymore with people like that.

[johngreene]

In any case, being abrasive is not helping.

John thinks he knows everything and the rest of us know nothing. He has no respect for anyone else, even those who have worked in electronic design for the last 50 years or more.

I see no point arguing or engaging in this forum anymore with people like that.

I've been working as an electrical engineer professionally since 1983. I am primarily an RF/communications designer specializing in UWB. I have "some" experience. I've been a member of this forum since it's inception and have helped numerous people. I had to take a break since around 2006 for potential conflict of interest reasons. But that arrangement has recently been dissivolved so I thought I would come back and participate again. Since I am currently bed-ridden, there isn't much else I can do. Unfortunately. Sorry for offending you.

[antonis]

 

Guys, plz...
Nobody (intentionally) insults anyboby..

[FSFX]

Guys, plz...
Nobody (intentionally) insults anyboby..

It has never been my intention to insult anyone here and on any other forum or FB group and I do actually mentor a lot of beginners, an activity that enjoy immensely and willingly to pass on the many decades of experience I have in working in the electronics and communications industry.
I got my first qualification in radio electronics in 1965 and during a very long career covering radio, microwave, computer hardware and software and data communications systems design for some very large and well know international companies I have gathered a large amount of qualifications and certifications relevant to everything I post.
I just don't like being treated like an uneducated idiot by some people, as I am sure a lot of the other well qualified people here must feel when they get certain types of responses to their valuable contributions.

[Phend]

I know the basics, to start with, never play with electricity when doing the following :
(going back to the very first post)

to get my fingers wet

.

[johngreene]

Guys, plz...
Nobody (intentionally) insults anyboby..

It has never been my intention to insult anyone here and on any other forum or FB group and I do actually mentor a lot of beginners, an activity that enjoy immensely and willingly to pass on the many decades of experience I have in working in the electronics and communications industry.
I got my first qualification in radio electronics in 1965 and during a very long career covering radio, microwave, computer hardware and software and data communications systems design for some very large and well know international companies I have gathered a large amount of qualifications and certifications relevant to everything I post.
I just don't like being treated like an uneducated idiot by some people, as I am sure a lot of the other well qualified people here must feel when they get certain types of responses to their valuable contributions.

If it matters, I couldn't participate on this forum for 16 years because I was consulting for a major pedal manufacturer designing all of their pedals. "for fun" lol.
My primary day job for the last 12 years designing an UWB radar to aid surgeons performing lumpectomies on breast tumors. I am co-inventor of this product: https://www.merit.com/merit-oncology/localization/breast-soft-tissue-localization/scout-radar-localization/. Prior to that I worked on wifi modems and cable modems mostly with a brief stint designing HF and VHF military radios. Back in the day when RF design required a lot of discrete components instead all being integrated into a single IC like they are today. There goes half my career!
We got off to bad start so can we agree to start over?

[RandyBeast]

Now that the battle is over, I am doing some redesigning of the circuit and will lay it all out on a breadboard. I will send a video of my results and then get another PCB designed. I will also send a new schematic with it and will explain my thought process.

John, thanks for your input, it's been very helpful.

[Dormammu]

The original scheme contains many unnecessary components and several errors.
I'm guessing the transistor stages don't really work, and all the gain comes from IC.

[johngreene]

Another point regarding stability of negative ground PNP Fuzz Faces is the the decoupling capacitor on the fuzz pot on the emitter of Q2 should go to ground rather than be connected to the +ve supply. That way you have the lowest impedance path to ground. If you have it connected to the +ve supply then the emitter decoupling capacitor and the power supply decoupling capacitor are in series and form a capacitive voltage divider. This means that some of the signal from Q2 emitter (which looks a bit like an emitter follower and thus has a low output impedance) gets feed back onto the +ve power supply. A good recipe for instability, oscillation and motorboating.

I disagree. The emitter is referenced to the +ve supply rail. The pot should be connected to the same reference rail as the emitter of the transistor it is connected to.

Looks like we may have both missed that he has a series 120 ohm resistor in line with the pot. I assumed that is to set a maximum gain by not letting the emitter resistance go below 120 ohms. Connecting the capacitor to either supply would also bypass this resistor.

[RandyBeast]

The original scheme contains many unnecessary components and several errors.
I'm guessing the transistor stages don't really work, and all the gain comes from IC.

The transistor stage works fine as I breadboard it before adding the gate circuit. the Grn diodes has a 3.3V drop, so the high gain there is to just get back the volume that was lost. thanks for your input though. if you would explain the errors, that would be helpful too.

thanks

[RandyBeast]

Another point regarding stability of negative ground PNP Fuzz Faces is the the decoupling capacitor on the fuzz pot on the emitter of Q2 should go to ground rather than be connected to the +ve supply. That way you have the lowest impedance path to ground. If you have it connected to the +ve supply then the emitter decoupling capacitor and the power supply decoupling capacitor are in series and form a capacitive voltage divider. This means that some of the signal from Q2 emitter (which looks a bit like an emitter follower and thus has a low output impedance) gets feed back onto the +ve power supply. A good recipe for instability, oscillation and motorboating.

I disagree. The emitter is referenced to the +ve supply rail. The pot should be connected to the same reference rail as the emitter of the transistor it is connected to.

Looks like we may have both missed that he has a series 120 ohm resistor in line with the pot. I assumed that is to set a maximum gain by not letting the emitter resistance go below 120 ohms. Connecting the capacitor to either supply would also bypass this resistor.

Yeah, I tried to set a minimum feedback resistance to see if it would help with oscillation then later realized I connected pin two of the pot to the wrong spot. my ned revision will not have this resister as the last board worked as log as the was an impedance buffer at the biggining, so I am breading today.

thanks

[FSFX]

Looks like we may have both missed that he has a series 120 ohm resistor in line with the pot.

I did spot the 120 ohm resistor but it seemed a bit of an unnecessary thing to have there in reality.

[Dormammu]

RandyBeast
The original FF has enough gain. Part of your scheme with IC is not needed. R14 is too much value. No suppressing oscillations resistors on inputs and small cap in NFL of IC1A.
The best choice is to build on IC two MXRdist-like things, without tranz part. And separately build FF.
1-st MXRdist must to be modified with lesser gain and no clipping diodes (for clean sound).

[RandyBeast]

Another point regarding stability of negative ground PNP Fuzz Faces is the the decoupling capacitor on the fuzz pot on the emitter of Q2 should go to ground rather than be connected to the +ve supply. That way you have the lowest impedance path to ground. If you have it connected to the +ve supply then the emitter decoupling capacitor and the power supply decoupling capacitor are in series and form a capacitive voltage divider. This means that some of the signal from Q2 emitter (which looks a bit like an emitter follower and thus has a low output impedance) gets feed back onto the +ve power supply. A good recipe for instability, oscillation and motorboating.

I disagree. The emitter is referenced to the +ve supply rail. The pot should be connected to the same reference rail as the emitter of the transistor it is connected to.

Looks like we may have both missed that he has a series 120 ohm resistor in line with the pot. I assumed that is to set a maximum gain by not letting the emitter resistance go below 120 ohms. Connecting the capacitor to either supply would also bypass this resistor.

Ok here is a Video and new Schematic. after considering all your input, I went with scratching the gate circuit. after cleaning and filtering the power, and switching to silicon transistors, I really didn't have that much noise that needed to be gated. check out the video, when I switch capacitors, you can hear quite the tone shift. I'm thinking I might want to lower the 1uF to maybe something like 220nF. it just seems to be very muddy and to much low end. I put a buffer in the front with a 5.1K impedance resistor to insure the impedance stays consistent throw this pedal. I did try bypassing the buffer to see how that worked and it was fine. however, when plugging other pedals in, it doesn't play nice anymore, so the buffer insures it plays nice with other pedals.

https://youtu.be/tqmksPqH4Fg (Video of the pedal on Breadboard)