Technology of the Big Muff - What does what?

[Solidhex]

 R6 is mentioned as being part of a bias network for the first transistor. Since its dc isolated by C3 how does it effect the bias of the Q1?

--Brad

[frequencycentral]

I think R6 isn't needed really, I left it out of my last BM. Probably just there so the pedal still passes sound with the Sustain pot at minimum - so as not to confuse the hard of thinking.

But making R12 into an external pot sound like a cool idea.

[John Lyons]

 Just so you don't have to go back to page one to see the schematic.



I wouldn't think that R6 does anything but set the lower limit of the
sustain knob.

[R.G.]

I see two R6's. 

[frequencycentral]

I see two R6's. 

Two R6's? Here be mojo! I was referring to the lower R6 of course.

[Greg_G]

And the upper one affects bias..

Great thread !

[Solidhex]

Ah

  Double R6's that's what messed me up. Yeah the one from the sustain pot I can take or leave. I never have the sustain set all the way off and its too small a value to effect the tone... Ok back to the stage by stage breakdown of the muff. Where we at?

--Brad

[John Lyons]

Ok, fixed the schematic so the 1K which was the second R6 is now R7.

I can't think of anything left to ask about. I'll boil down the replies here and make any easy reference chart with notes.
There will probably be some additional comments at that point.

Edit: Bah! now there are two R7s...I took out R7 as the Sustain pot, we all know what that does.

John

[frank_p]

Thanks John.  When Mike started his -paralysed by too many options-  topic.   I was saying to myself: "mhhh.. no technology of the Big Muff at GEO...".  And there it appeared instantly.  Great initiative !

[Gila_Crisis]

need more infos???

just look here: http://www.aronnelson.com/gallery/main.php/v/Gila_Crisis/Big_Muff/Big_Muff_Pdf/

[Solidhex]

Whoa

  I don't think I've seen that before Gila. Really thorough and easy to understand.

--Brad

[Greg_G]

Can I throw this thread back in the ring..
It seems to discuss some issues concerning gain that haven't been discussed this time around.

http://www.diystompboxes.com/smfforum/index.php?topic=60143.0

[Gus]

for fun

Use 2 dual opamps.  Use the same feedback resistor values and caps to keep the gain close to the transistor stages.  Make the first 3 stages inverting opamp stages and the last stage a noniverting stage.  Vref at 1/2 supply.  It should be interesting how close the sound is or is not to the transistor version.

Why I posted about the first stage in some detail is fuzzes that have non perfect virtual ground inputs like the FF and bmp are often liked maybe a more detail look into the interaction of the source and input.  The guitar is part of the feedback equation.

[welcomb]

I'm looking into putting a blend switch/knob in the BMP. I'm guessing since the first stage is a buffer, is it possible to get a bypass by connecting the collector of Q1 through a 0.1 capacitor to lug 1 of the volume pot, turning it into a blend pot? Or simply take a concurrent dry output from there?

Or is it better to make another buffer stage and split right at the input?

[John Lyons]

The first isn't a buffer. it's a booster.
You could add a buffer to the front
then take the output off the
emitter connected to one side of a100k pot
and then the output of the end of the BM
connected to the other side of the pot.
Then take the output off the wiper.
Maybe not ideal but it will work.

JOhn

[moose23]

Can someone explain r22. Does it work the exact same as the other emitter resistors? 

[John Lyons]

R22 sets the bias along with all the resistors to the right of C11.

John

[bumblebee]

RG: This is correct; C6 and C9 also have a varying impedance, and serve to lower the gain and hence the amount of clipping at lower frequencies. Making this smaller/bigger, causes less clipping at bass/more bass to be clipped.

While I'd hope this is well known around here  I'd also like to add that the difference between a 47nF cap and a 1uF cap in C6 and C9 is huge. At the smaller end you can have a very boomy big muff that doesn't do chords well on the low E/A strings, at the other if you have  1uF's in there it handles chords very well.

A lot of people find Sovteks boomy as hell, that's primarily because of C6 and C9 being 47nF (some triangles/ ramsheads are affected by this too with C6 and C9 being 50nF) and once you up them to 1uF the boom is gone. Another thing to note is that once you up C6 and C9 it will give the impression of having less bass overall so you may need to increase the majority of the .1uF caps to 1uF also to compensate.
A good place to have the .1uF caps is C4 and C11, use 1uF for all others.

In some cases, and it is always individual pedal dependent and also what amp you're using to a certain degree, you can get rid of the boom sufficiently with as low as 220nF caps in C6 and C9.



C2,5 & 8 determine the high frequencies cut off point. The higher the pF the less highs come thru. Try replacing the 470/560pF caps with 100pF (or even 50nF) for more high freqs while at the same time retaining the scooped mids of the trademark tone stack and the same bass level. Doing this is particularly useful in an un-ordinarily dark sounding big muff.

I really have no idea why things do what they do in any circuits, I just know what does what from personal experience learned from trial and error.

This thread is great BTW, I can finally learn the technical reasons behind why things happen rather than just knowing that they do happen!

[quarara]

In some cases, and it is always individual pedal dependent and also what amp you're using to a certain degree, you can get rid of the boom sufficiently with as low as 220nF caps in C6 and C9.

hey, this is what skreddy did in the mayo!

[bumblebee]

I have that schem somewhere i think, I've never really even looked at his schems much, not for a long time anyways.