Big Muff Pi Blend Build

[Barcode80]

So, I've been working on this Big Muff Pi for a friend of mine (i may have posted already about this, if so, sorry, i just can't remember) and i have a "clean" knob wired in to dial in unaffected signal. itis wired something like this:


my question is, do you think i need a buffer on there to keep the clean pot from loading the signal, or do you think a cap across the signal lugs would be good, or do i need anything at all? the vol pot i was going to use is 50k by the way.

[hendriko]

excuse my (probably extreme) n00bness, but when the switch is in bypass, aren't only the bottom 2 rows of lugs "selected", so wouldn't that pot not do anything?

just wondering...might be (probably are like i said) wrong here

[Barcode80]

when the effect is in bypass, it isn't supposed to do anything. it's purpose is to allow a controllable amount of clean signal to mix with the distorted signal. unless i'm mistaken, this should give me one knob to control the volume of the muff (via the muff volume pot) and then dial in some unaffected signal via the extra volume pot. this is being made for bass, so i want a clean mix in there for the guy i'm making it for.

[hendriko]

oh my bad then...i thought you wanted a volume control for when the pedal is in bypass (clean sound)

[mills]

Thanks for asking, I'd just wondering about this out myself.  (sorry, I'm of no help, just watching for an answer)

[Processaurus]

Don't think that will work out very well.  It makes a feedback loop from the BMP out to in through the clean blend pot.  Also it connects the weak guitar signal to the much lower impedance output of the effect.  Consider routing the clean (with or without buffer, I'd just buffer it and be done with it, that would work better with your 50K pot) to its volume pot, and then use a high value resistor, and coupling cap, from the wiper to the base of the the last transistor (the LPB1 type stage that brings up the volume after all the distortion).  You might need a similar value resistor to put in series with the BMP signal coming from the tone control, to keep the two sources getting mixed from interacting.  A plus of this is you can get the clean louder than unity gain.

Big Muff with the clean blend is outstanding on bass, sometime I'm going to try one with a clean blend with a LP filter type tone control (or maybe just routed to the LP side of the big muff tone control), so you don't hear the telltale attack of the clean, but get a natural dynamic in the bass frequencies.

[Barcode80]

hmm, i'm having trouble picturing what you said. is this what you mean?


sorry, when it comes to signal impedance and things like that, i'm a bit green. 

[mills]

Sorry, I've been doing to much reading on here lately and am having a bit of trouble grasping exactly what we need to do ( I know theres lots of general blenders on here, but keeping it small would be nice).  Is this drawing close?  Buffer/split it (the B) send one half to the muff, the other to a volume control (and possibly a lowpass tone trimpot ) then meet them up at the base of the last stage in the muff? (ignoring that this picture lost something in the save, and leaving out the resistors that were mentioned.  With those, would we just look at it similarly to another stage of the big muff and use similarly valued coupling cap and resistors?



Alternatively, I had originally intedned to play with the brassmaster clean mix.  would this basically work with the top (blank) path heading off through the muff, and meeting up with the clean as shown?  Except in the red box, we have the last muff tone stage, in the blue we have the muff tone control, and in the green we have the similarly valued resistors, and the coupling cap after they join?  As the wiper of the tone pot which usually goes to the base of the transistor doesnt typically have a resistor off of it, will this alter the values in our tone stack? (I know, I'm massively new at this so thanks for the patience and help)

[cab42]

Recently I build a Bazz fuzz for the bass player I play with, and we found out that some kind of blend control would be beneficial.

I decided to go for SeanM's B.Blender as a stand alone unit for flexibility, but Sean also had a Minimal blender using a single JFet or a single opamp.

Maybe that is what you need. Here's the link: http://www.seanm.ca/stomp/minblend.html.

Regards

Carsten

[Barcode80]

senas blender would likely work, but not with the functionality i need. i need discrete level controls for each, as i don't want turning up the clean to mean having to turn down the fuzz. plus, the box is etched and labeled already. i could do it that way though. would the send and return tips just be wired to the muff in and out?

[royzic]

i would try doing it the way it is done in the ampeg scrambler.
it seems to be simple and effective.

looking at the scrambler's schem, i see the blend pot connected to the end of the circuit by log 3
log 1 of the blend pot is connected to the output of the first stage
and log 2 goes to the output.

that might work in the big muff too

-Roy

[Processaurus]

Hi, Barcode, you nearly got what I was thinking about, I looked at the big muff schematic at ggg and I think you can leave out the coupling cap and just connect your 1M resistor to the connection between C12 and R20 (the tone knob).  My instinct would be to go with a smaller resistor than 1M now, maybe 50K?  And also add a 50K between the wiper of the tone knob (R20) and C12, so both new resistors meet at C12, and get mixed together.

[Barcode80]

out of frustration over not getting this blend thing figured out and discovering the big muff i built is a dud, i built a RAT. WHOAH this thing sounds great. tungngruv gave me one of the old vintage 308's for it a while back, and it really makes a difference. goes from nasal scream to good warm and thick distortion. i think i'm going to sub it in the big muff's place if i can at least get the blend going. i tried building the minimum blender, but it didn't seem to work. i got no signal through it. could have been my layout, although with like 6 parts, i can't imagine that's the case.

[mills]

Hi, Barcode, you nearly got what I was thinking about, I looked at the big muff schematic at ggg and I think you can leave out the coupling cap and just connect your 1M resistor to the connection between C12 and R20 (the tone knob).  My instinct would be to go with a smaller resistor than 1M now, maybe 50K?  And also add a 50K between the wiper of the tone knob (R20) and C12, so both new resistors meet at C12, and get mixed together.

Sorry for the probably stupid question, but can I just put two wires off the switch, and bring the clean wire back into the circuit before the last gain stage (plus volume pot, and 50k resistor)?  I'm pretty new to this, but I thought that I'd read in one of the FAQ's that one should buffer before spliting the signal...  is that just preferable but not essential?  Also, if its not asking too much, are the 50k resistors simply to get the impedances into the same ballpark for mixing before they hit that last gain stage?  (and if so, why so high relative to the 8.2-10k seen in the other stages)

(not questioning whether you are right, just trying to sort out everything in my head while planning the build)

[Processaurus]

Sorry for the probably stupid question, but can I just put two wires off the switch, and bring the clean wire back into the circuit before the last gain stage (plus volume pot, and 50k resistor)?  I'm pretty new to this, but I thought that I'd read in one of the FAQ's that one should buffer before spliting the signal...  is that just preferable but not essential?  Also, if its not asking too much, are the 50k resistors simply to get the impedances into the same ballpark for mixing before they hit that last gain stage?  (and if so, why so high relative to the 8.2-10k seen in the other stages)

(not questioning whether you are right, just trying to sort out everything in my head while planning the build)

Its a good question and you're right, on principle it's preferable to buffer things when you split them, then there is no chance of interaction from one part of a circuit to another, its like a turnstile at the train station, you can only go one way.  Also when you split your signal, it has to deal with the lowered impedance from driving both loads, which can be hard on guitar pickups and suck the treble.

The 50K resistors I suggested were just some minimal attempt at getting a little bit of a summing stage going on, the idea being that the current from each source has an easier time getting to the amplifier input than messing with each other.  like this:



If you're going to try this I'd stick the ggg jfet buffer between the input and the clean vol pot, that should sort out any potential impedance mismatching issues and present the guitar with a high impedance input.

[mills]

Excellent.  Thanks for the help and understandable explanations!