Simple fuzz design - I hear an octave down but didn't mean to!

[sebotron]

Hi! First, my name is Sebastien. I've been studying electronics and experimenting with effects building for a bit over 6 months now and all is going well. I do a lot of reading and usually try to design my own, albeit very simple still, circuits from what I have learned rather than build existing ones. I usually post on Reddit on /r/diypedals but I thought I'd start posting here too.

So, a couple days ago, I was toying with pretty standard cascaded npn gain stages hoping to end up with a nice little fuzz. I ended up with 3 identical stages followed by 2 clipping LEDs with different Vfs and a simple volume pot. (I'll link the schematics in a bit)

While trying to figure out how to play with the total gain with one pot, I decided to link the first 2 stages' collector to the same pot just to see what would happen. My still limited understanding of electronics lead me to think that whatever the pot's value was at, it would be applied in parallel to both collectors, feeding them with the same DC current and thus, affecting gain.

When I started playing, I noticed I had lost a lot of gain, as expected - but I was also hearing a clear octave down under every single note I played. Now I'm trying to figure out what exactly is causing this. Disconnecting the LEDs remove the octave.

So here's the schematics of what I have on my board right now: http://imgur.com/zNML47c

Here is a somewhat poorly played recording of what I can hear: http://clyp.it/v4anll54

Here's my signal path: Fender Jaguar Thinline SE -> my circuit -> Orange Micro Terror -> Custom birch cab w/ 1x12 Celestion Blue -> sm57

Maybe it's not even an octave, maybe I'm just hearing things and maybe it's just some funky harmonics playing games with my ears but anyhow, I would like other people's opinions.

Thank you!

[PRR]

> link the first 2 stages' collector to the same pot

Cascaded adjacent stages are OUT-of-phase.

Connect them together, not much good can happen. They wanna cancel.

Connect _three_ stages on one "soft" power supply, output stage sneaks-back to input stage in-phase to make oscillation. Not that simple, Bode wrote a paper, but Murphy's Law says that if you don't want an oscillator, you will get one.

And if you don't quite get oscillations, what you can get is not-quite oscillation, "ringing".

And I suspect your 0.1u+1Meg coupling networks. They are nominally the bottom of the audio band (more like 70Hz). If several 70Hz corners cascade enough phase-shift to almost oscillate, note in the 200Hz range could excite long-ringing 100Hz tones.

[sebotron]

This is embarassing, I had totally forgotten about phase shifting.

The first half of your explanation makes sense to me, but I fail to see how the R-C networks contribute to producing oscillation. Is oscillation a symptom of the subsequent phase-shifting of a frequency band through multiple stages? Can it be avoided?

I'll admit I do kind of like the sound it makes though... 

Thank you for your answer!

[PRR]

> I fail to see how the R-C networks contribute to producing oscillation.

"Phase Shift Oscillator". Don't make me re-type 75 years of common technology.

[bool]

>>> I'll admit I do kind of like the sound it makes though...

Lucky you! So why are you complaining then?

[sebotron]

"Phase Shift Oscillator". Don't make me re-type 75 years of common technology.

I'm sorry, I haven't been doing this for very long. Thank you very much for your help!

[storyboardist]

I think it sounds pretty cool. Reminds me of something Dan Auerbach would have on his board.

[monksanto]

I agree, sounds cool.

The Bazz Fuss delivers an inverted signal, doesn't it? What is the problem with an "out-of-phase" signal unless you are hooking up pedals in parallel?

(sorry, this is a real question, not a facetious reply  )

[Eddododo]

I agree, sounds cool.

The Bazz Fuss delivers an inverted signal, doesn't it? What is the problem with an "out-of-phase" signal unless you are hooking up pedals in parallel?

(sorry, this is a real question, not a facetious reply  )

He is referring to the connection of the collectors in sequence

[storyboardist]

I've listened to the clip a couple times now and I'd like to give it a go on my breadboard. What kind of transistors did you use? What value on the vol pot? 100k?

[sebotron]

I've listened to the clip a couple times now and I'd like to give it a go on my breadboard. What kind of transistors did you use? What value on the vol pot? 100k?

All trannies are 5088s, gain pot is 10k and vol pot is 100k.

[duck_arse]

I had a go today with cod-ordinary bc548b's sounded like something. I think you need a resistor in series with the gain pot, so you don't connect yr transistors across Vcc and ground.

I found a million ways to make this into a radio, very unstable, if your leds light with no signal in, you're oscillating. some fun if you put a 22k between the first collector and 100nF cap, with a 47nF at that junction to ground.

another of the rare "E1 series" circuits. and you really need to think of a better name than "octave?".

[WhiskeyMadeMeDoIt]

I built it and posted on the other website he has posted this to...it will remain unnamed...
http://imgur.com/a/W3n9o#0
Breadboarded and scoped it.
Red is output and yellow is input. You can see ringing on some notes. I think is just sounds like a fuzz with a slightly "mis-biased" collector and occasional ringing.
What do you experts see that i don't. BTW it sounds ok.