Big Muff build questions

[oliphaunt]

I am building a Ram's Head Big Muff from these schematics found here:
http://www.pisotones.com/BigMuffPi/psst/BMP_versions.htm
and here:
http://www.generalguitargadgets.com/pdf/ggg_bmp_ram_sc.pdf

(Should I just post these schematics to make it easy or is it not cool to link to other web site's images?)

The only difference I see between them is in the tone section, the AMZ traced schematic has a .1 cap rather than .001.  I have seen .001 from other scources, so I went with that one.

I put this together on my breadboard this evening, and it works.  I used only carbon comp resistors, 5088s, ceramic and greenie caps and standard electrolytics.  It has enough output to drive a small city.  The heavy distortion is there when the sustain pot is wide open, but it gets a bit sputtery and weak very quickly when the sustain pot is lowered.  Even at full the sustain is not as "singingy" as I remember it, it has some bloom and then dies failry quickly with single notes though chords hold out longer.  A big issue is the tone.  I'm comparing it to the clips found here: http://www.stompunderfoot.com/BIG_MUFFS.html.  I don't have a real Muff to compare it to, and don't really know anyone in my area who does.  But this has a huge, almost out of control bass, and the high end is very muted.  Granted, this is not my kind of tone to begin with so I am out of my element and not sure what to expect, but I am looking to get that Gilmour thing going on.

As I built it on the breadboard I tested the output of each "module" as I think of them.  I built just the first input boost section and listened to it .  Right off the bat the tone was very muted due to the 560p cap in the feedback loop.  Removing this cap brings back the high end.  I figured that was ok, gain stages down the line might add a lot of high harmonics so you might want to tame those early on.  Then I built the first distortion stage.  Again the tone was further muted by the same cap in the loop.  And so on, the second distortion stage making it even worse, so that at this pint it sounds like a garbled mess.  I hoped the tone control would add it back in some way, and it certainly does make things more useable.  The final buffer stage didn;t make much difference(what is the purpose of this final stage, gain makeup as if there wasn't enough gain?).  But it's not there.  I can remove the 560p caps and get the high end.  I suspect I can lower them, though I don't have the 470p cap I see from other versions on hand (it's orded and will be here maybe tomorrow). 

The only Muff I have played in the last 20 years was a modern "Little Big Muff".  I remember thinking the low end on it was out of control and needed to be tamed, but I thought the high end was still very present.  Does anyone have any thoughts?  Am I just missing what a Muff is all about?  Maybe I need to try anoither version?

[El Heisenberg]

Ugh, im on a big muff quest too. My third big muff. Ive built triangle, reissue, and have black russian breadboarded.

Rams head is sposed to be boomy i think. What youre describing is exactly what I get from my muffs. Gilmour used a triangle version. Its my favortie so far. But with each version i dont get crazy violin-like sustain. Is it the transistors? The clipping cap? Coupling resistors? Biasing? 

[petemoore]

but it gets a bit sputtery and weak very quickly when the sustain pot is lowered.
  Certainly calls for a bias check of the transistors after the sustain pot.
  See "What to do when it doesn't work" stick/thread, follow the instructions.
 

[oliphaunt]

I let this build sit for a while and have come back to it today.  Sometimes I need a fresh ear to decide what is working and what is not, as you get very invested in a new build.  I have decided the treble is fine like it is, I  just needed to get used to the mid scoop sound.  I have a few more questions though:

but it gets a bit sputtery and weak very quickly when the sustain pot is lowered.
  Certainly calls for a bias check of the transistors after the sustain pot. 

I think the issue here was that I was using an log pot rather than linear.  I swapped it for for a linear pot and  now the control works better over a larger range.    Now my big question is, should the Muff "fizzle out" after a long sustain?  Again, I have been through this many times and was extremely careful building it, checking each stage before going on to the next, so I feel quite certain it is put together "correctly".  It has huge sustain, but just before it tapers off to silence the sound fizzles and quickly dies out.  Maybe that's how it should work, with the huge amount of compression and clipping going on, but I don;t have a real Muff to test against.  Does the real thing fizzle out at the very end of it's sustain?  What voltage should I be looking for for a correct bias?

I tried out the AMZ mid control mod described by another web site as: "Replace C1 with a 22n cap.  Replace R2 with a 22k to 25k potmeter (wired as a variable resistor) with a 1k resistor wired in series."  This makes for a nice extra control, but the center of the mid frequency is a little too low for my tatse.  Has anyone found some good values to raise the frequency center a little bit?  I'll be swapping caps , seeing what I can come up with...

Thanks!






What should the bias be? 

[petemoore]

  Does the real thing fizzle out at the very end of it's sustain?
  The ones I tried all 'panned over' to noise floor as notes die out.
  It sounds like it could be a nice feature though.
 

[oliphaunt]

  Does the real thing fizzle out at the very end of it's sustain?
  The ones I tried all 'panned over' to noise floor as notes die out.
  It sounds like it could be a nice feature though.
 

Thanks Pete.   By "panned over" do you mean smoothly transition to clean or silience?  Mine definitely has a drop off point, though it is well into the sustain, and not likely to be heard under normal playing circumstances.  I sure wish I had a real Muff to compare to...

[Wales]

I have built a few of the Big Muff's from the GGG site and have a friend who is also looking for a Gilmore type sound. My friend likes the triangle version and 70's versions best, he can't seem to decide between the two. With those versions and my green Russian version I do not notice the note drop off you talk about, but with my Violet Ram's head version I have the same problem. I have been trying to narrow the problem down as well and with no luck so far (however its been at least two months since i have had the time to look at it). For treble I find the Green Russina best, for mids the triangle withe the 70's in close second, and for bass the violet rams head.

Since you have it on the breadboard its nice with the muff you can just get a few different parts and swap it over to a different version.

That my cents, not worth much but.

Forgot to mention my friend won't use the muff without the ross compressor on as well. Gives alot more hang and sustain without colouring the distortion.

[petemoore]

By "panned over" do you mean smoothly transition to clean or silience?
  Nope, wouldn't call it silence, kinda noisy is the general consensus for the Big Muff Sound.
  Mine definitely has a drop off point, though it is well into the sustain, and not likely to be heard under normal playing circumstances.
  They all sound a little different.
  I sure wish I had a real Muff to compare to...
  That's a real Muff. Still curious what the Q voltages are though.
  Kind of a big build to just try another.
  First transistor boosts the signal, as should the 3 remaining transistors [minus some clipping and tone attenuations], which should mean any teeny input is treated as such...hard compression and boost.

[oliphaunt]

Here are my voltages with an 8.88v power source.  The transistors are 2N5133, I prefer the sound of them over 5088s.  The fizzy quality at the end of the sustain is the same with both transistor types.

Q1
C=7.04
B=0.59
E=0.02

Q2
C=5.5
B=0.65
E=0.04

Q3
C=3.91
B=0.67
E=0.04

Q4
C=4.91
B=1.31
E=0.78

These are mostly in the range of the GGG voltages I found here: http://www.generalguitargadgets.com/pdf/ggg_bmp_instruct.pdf
except for the Q1 C which they have as 3.9.  I don't know which version the GGG voltages are for though.

[petemoore]

C=7.04
B=0.59
E=0.02
  What does the resistance measure between the collector lead and the battery clip +? [should be between 10k and 20k]
  This Q1 gain stage isn't biased. Check every other resistor value of the first stage.
Q2
C=5.5
B=0.65
E=0.04

Q3
C=3.91
B=0.67
E=0.04

Q4
C=4.91
B=1.31
E=0.78

[oliphaunt]

What does the resistance measure between the collector lead and the battery clip +? [should be between 10k and 20k]

The resistance is 10k

This Q1 gain stage isn't biased. Check every other resistor value of the first stage.

I checked (measured) every value of every component in the first stage and went over the schematic several more times and found no errors.  The collector bias is still 7.4v.

I also just rebuilt the first stage according to this schematic:

I built this on a separate breadboard with no input or output, just the circuit and 9v power in, so I could test just this stage without any possible interference from the rest of the circuit.  All the values are essentially identical to the complete circuit.  I can raise the value of the 10K R5 to lower the voltage at Q1, it takes a 220K resistor to get the voltage to around 5.  It sure seems like this is how this circuit wants to work.  Does anyone see anything I am missing?

[oliphaunt]

What does the resistance measure between the collector lead and the battery clip +? [should be between 10k and 20k]

The resistance is 10k

This Q1 gain stage isn't biased. Check every other resistor value of the first stage.

I checked (measured) every value of every component in the first stage and went over the schematic several more times and found no errors.  The collector bias is still 7.4v.

I also just rebuilt the first stage according to this schematic:

I built this on a separate breadboard with no input or output, just the circuit and 9v power in, so I could test just this stage without any possible interference from the rest of the circuit.  All the values are essentially identical to the complete circuit.  I can raise the value of the 10K R5 to lower the voltage at Q1, it takes a 220K resistor to get the voltage to around 5, but I lose some sustain and gain and the fizzle is still there.  It sure seems like this is how this circuit wants to work.  Does anyone see anything I am missing?

[oliphaunt]

Well, I finally figured this one out.  I borrowed a Little Big Muff to compare how it acts and it was obvious I had an issue, but I had gone over my schematic and my build dozens of times and everything seemed right.  Today I happened to be looking at a different Muff schematic and I discovered that the position of the diodes and the cap in the feedback loop were reversed in each clipping section (D1, D2, and C6) in the version I was working from, a Ram's Head schematic credited to AMZ: http://www.pisotones.com/BigMuffPi/psst/BMP_versions.htm.  All other schematics I have found look like this one:



I reversed the diodes and cap, so they look as seen in the picture above, and now the fizz is gone now, it fades smoothly into Muff noise. It also changed the tone, giving it a woody thwack with more useful upper mids than the modern Muff, and maybe not quite as much distortion.  I can really hear the Wall era Glimour sound in this thing now!

Obviously this is the difference, can someone explain exactly what is happening here?  I'm guessing there was poitive voltage on the diodes in a way they didn't like.

Now that everything works I've found I prefer the tone with the cap (C2) in the feedback loop of the boost section removed, I think it opens it up just a bit without making it overly bright.  I will probably socket all those caps in the final build so I can experiment more with them down the line.

Thanks for the help on this (in this thread and the many others I have searched), hope this helps someone else with similar issues!