Big muff pi feedback path questions (cap/diode order)

[Boner]

https://www.electrosmash.com/big-muff-pi-analysis
https://www.electrosmash.com/images/tech/bmp/big-muff-pi-v3-clipping-stage.png

In the bigmuff pi, does it matter if its cap/diode or diode/cap in between the collector and base of the BJTs?

If the feedback cap is connected to the collector first, would this feedback cap somehow "mess" with the bypass cap (to connect to a following stage) that is also connected to the collector? By "mess" with, I mean lets say you have a 2.2u feedback cap and a 100n bypass cap, would you still get that soft clipping effect through the entire audible spectrum since 2.2u is a basically a short at low frequencies and 100n isnt?

Also, can I go ahead and replace the electrolytic cap with a film type? I kind of hate the leakage associated with electrolytics

[idy]

The order does not matter, they are in a series and the feedback loop doesn't "know" which comes first. Yes, film is fine, you are probably using a version that calls for 1uf. Many versions call for a smaller value, and may be cutting a little bass. 1uf makes a pretty fat muff, I doubt you would actually want to increase that. (And 2.2uf film cap would be hard to find....)

The other cap that bypasses the diodes is usually smaller than 100n! more like less that 1n as in your examples. That limits the "bandwidth" cutting some highs and preventing the whole thing from oscillating.

[antonis]

https://www.electrosmash.com/images/tech/bmp/big-muff-pi-v3-clipping-stage.png
the bypass cap (to connect to a following stage)

Bypass caps are C12 & C11 - Coupling caps (connecting to following stages) are C5 & C13..

<off-topic ON>
IMHO, the use of C6 & C7 polarized caps should be avoided..
They are set with correct polarity in relation with DC bias but they're almost always working back-biased on AC due to NFB and high gain configuration..
Non-polarized caps, electros or not, should be a much better choice..
<off-topic- OFF>

[Boner]

They are set with correct polarity in relation with DC bias but they're almost always working back-biased on AC due to NFB and high gain configuration..
Non-polarized caps, electros or not, should be a much better choice..
<off-topic- OFF>

So the cap is reverse biased in audio due to negative feedback? I don't understand.

I don't understand the idea of "reverse biasing" (if thats what back biased means) in caps. The whole point is to block DC right? So why would it matter if its AB or BA? Anything above or below ground is filtered out correct? Everything else is passed on thru

[idy]

Most electrolyte caps are polarized, they have a + and a - side. It is bad for them to experience reverse voltage, they may blow up (not likely here) or wear out more quickly, or sound poorly.
In that feedback loop they will experience voltages back and forth. The voltage on the + side will/may sometimes be lower than the -. So film caps or non-polarized electrolytes are preferred. But polarized have worked "well enough."

[antonis]

What idy said...!!

For a signal of 1V, say, Q3 base sits on 1.7V (DC+AC) whereas collector sits on about 250mV (CE_SAT - negleting V_E of some tens of mV).
That forms a "reverse" voltage difference between C6 negative & positive leg..

[Boner]

BLAST! I was getting my wording all mixed up. 

I understand, thanks all! Definitely a lot of help...

...now I'm curious about the bypass cap and resistor in the feedback path. Is this just to limit the higher frequencies to tone down the harshness? I'm seeing that resistor/cap as a lowpass filter.

For the sake of argument, lets say you went with jfets instead of bjts, would you still want an RC filter in the feedback path or could you skip it because the miller effect limits it anyways?

[antonis]

...now I'm curious about the bypass cap and resistor in the feedback path. Is this just to limit the higher frequencies to tone down the harshness? I'm seeing that resistor/cap as a lowpass filter.

Partially true..
(actual feedback cap/resistor configuration forms a HPF but its specific placement inside feedback loop "turns" it into LPF - more highs "sneak" out of voltage gain, hence less amplified..)

You might also see that bypass cap alone (usually of a value of ten times lower) in the feedback loop in case of different bias method (considering CE junction almost open circuit due to reverse bias) with a sole task of preventing high frequency oscillation/squealing on a high gain configuration..

For the sake of argument, lets say you went with jfets instead of bjts, would you still want an RC filter in the feedback path or could you skip it because the miller effect limits it anyways?

Miller effect reflects capacitance in the range of few pF where feedback cap values are in the range of few tens or even hundreds of pF..