Ok, seems like a popular pedal and has been for many many years.
Lets figure out what does what. Making a value higher or lower does what?
(http://www.basicaudio.net/Big-muff-tech.jpg)
I'll start the ball rolling.
R1 A Pull-down resistor to drain any DC voltage to ground from C1. Helping reduce "popping"
Any value from 1M to 2.2M is fine, no change in sound.
C1 Sets a high pass filter along with R3. Smaller cap = less bass and a little less signal into the circuit.
R2 Limits the signal in a bit as well as setting the impedance. Bigger lowers the impedance and signal.
R4 Is a feedback resistor which works along with R3, R5 and R6 to bias the transistor. Smaller = less gain
as it lets more feedback flow from collector to base.
C3 is a "coupling cap which forms a low pass filter with R7. Bigger = more bass (and signal) passed.
C2 across the Base and Collector rolls of some high end. Bigger + more roll off.
Next person...
John
I would add that aside from any tone-shaping function, the purpose of C3 is to keep DC from R6 off the sustain pot R7 and the base of Q2 (which is biased by its own network consisting of R10, R9 and R13). R7 controls the amount of signal passed from Q1, a booster, to Q2, by shunting an adjustable amout of signal to ground.
The components surrounding Q2 are the same as those surrounding Q1, with two important exceptions: the addition of D1, D2 and C6 to the feedback network of the transistor, and the lack of a "sustain" control after it. D1 and D2 are back-to-back diodes that are referred to as "clippers" or "clamps", because they clip the waveform (creating what we hear as distortion) and clamp the dynamics of the signal (creating what we hear as compression or sustain). C6 reduces the amount of bass that goes through the clippers.
Thanks for this.. they're always a good read.
I believe C6 is primarily there to block DC through the diodes, which would affect bias.
R5, R13 and R16 (the emitter resistors to ground) can be lowered to raise the gain, I've heard of people shunting the emitter directly to ground for a crazy - over the top fuzz. Conversely, you can reign in an unruly fuzz by raising these values.
The collector resistors (R6, 11, 17 and 25) were components that saw a lot of different values over the years too. Anywhere from 10k - 22k. Lowering these values also tends to raise the gain.
One last thing, R6 is there to control the lower limit of the sustain pot. without it (like on many triangle versions) you get no sound with the sustain rolled all the way back.
Quote from: station on July 29, 2009, 10:43:59 AM
The collector resistors (R6, 11, 17 and 25) were components that saw a lot of different values over the years too. Anywhere from 10k - 22k. Lowering these values also tends to raise the gain.
I've seen them as high as 33K.
Quote from: station on July 29, 2009, 10:43:59 AM
One last thing, R6 is there to control the lower limit of the sustain pot. without it (like on many triangle versions) you get no sound with the sustain rolled all the way back.
I don't think I've ever seen a triangle w/o R6. The lowest value I've seen for it is 820 ohms.
Quote from: station on July 29, 2009, 10:43:59 AM
R5, R13 and R16 (the emitter resistors to ground) can be lowered to raise the gain, I've heard of people shunting the emitter directly to ground for a crazy - over the top fuzz. Conversely, you can reign in an unruly fuzz by raising these values.
I did that on the Creamy Muff on my site. I don't think it gets that crazy but it sounds pretty good.
It not that simple. It has few thing going on a the same time. Some things to look up
Page 86 TAOE has something to look at. The added voltage drop across 100 ohm in the emitter leg adds to the Vbe drop
http://www.nd.edu/~hscdlab/pages/courses/microwaves/labs/Agilent1293.pdf Kind of like figure 6 but with an added emitter resistor.
Okay, I've never even looked at a Big Muff before. (Blasphemy to some, I'm sure.) But I'd like to know the reasoning, in detail, for the values chosen for the resistors on +9v: R6, R11, R17, R24, R25.
Thanks John for starting this!
Quote from: John Lyons on July 29, 2009, 12:26:53 AM
R1 A Pull-down resistor to drain any DC voltage to ground from C1. Helping reduce "popping"
Any value from 1M to 2.2M is fine, no change in sound.
Yep.
QuoteC1 Sets a high pass filter along with R3. Smaller cap = less bass and a little less signal into the circuit.
Yep, sets the input high pass along with everything else up to the collector and emitter of Q1, including feedback - see below.
QuoteR2 Limits the signal in a bit as well as setting the impedance. Bigger lowers the impedance and signal.
R4 Is a feedback resistor which works along with R3, R5 and R6 to bias the transistor. Smaller = less gain
as it lets more feedback flow from collector to base.
R2, R3 and R4 set up the input and feedback for the transistor. All play multiple roles. R3 and R4 do indeed set biasing. But imagine that you replace Q1 with an inverting opamp stage, the + input being biased else where. That would make the gain of this stage be Rf/Ri = R4/R2, right? That is what is happening here, excepting for the transistor having a lower input impedance and less gain than a purpose-designed opamp. Because of the transistor's "imperfections" the gain is lower than you'd get from an opamp with the same resistors, but the operation is very similar. It's an inverting feedback stage.
QuoteC3 is a "coupling cap which forms a low pass filter with R7. Bigger = more bass (and signal) passed.
Actually, with R7 and to some extent R8, which appears as a bigger load as the pot rotates to max. At the max setting, it's almost all R8, or rather, C4 and the input impedance of the next feedback stage at Q2.
QuoteC2 across the Base and Collector rolls of some high end. Bigger + more roll off.
Correct, in the feedback around the opamp sense. This capacitor appears just like a capacitor to ground but of a value equal to the effective gain with feedback times the real capacitance; this is known as the Miller effect, and this is sometimes called a "Miller capacitor".
Quote from: Greg_G on July 29, 2009, 10:01:12 AM
I believe C6 is primarily there to block DC through the diodes, which would affect bias.
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.
Quote from: station on July 29, 2009, 10:43:59 AM
R5, R13 and R16 (the emitter resistors to ground) can be lowered to raise the gain, I've heard of people shunting the emitter directly to ground for a crazy - over the top fuzz. Conversely, you can reign in an unruly fuzz by raising these values.
They control the open loop gain, and as such make the approximation to an opamp more/less valid as they get smaller/bigger. With lower open loop gain, you run out of feedback gain faster and have a lower overall gain, which decreases clipping.
QuoteThe collector resistors (R6, 11, 17 and 25) were components that saw a lot of different values over the years too. Anywhere from 10k - 22k. Lowering these values also tends to raise the gain.
Raising them tends to raise the open loop gain. I'm using gain in the strict sense of voltage out over voltage in, not "gain" the way guitarists say it, meaning more apparent distortion.
Quote
One last thing, R6 is there to control the lower limit of the sustain pot. without it (like on many triangle versions) you get no sound with the sustain rolled all the way back.
Yep.
Quote from: Gus on July 29, 2009, 11:02:17 AM
It not that simple. It has few thing going on a the same time.
Absolutely correct. Most things affect other things too.
Quote from: ayayay! on July 29, 2009, 11:13:02 AM
But I'd like to know the reasoning, in detail, for the values chosen for the resistors on +9v: R6, R11, R17, R24, R25.
6, 11, 17 and 25 are chosen for bias point/gain on the transistors in the open-loop sense. R24 is chosen as per the stabilized-bias setup I've typed in here many times to bias q4 properly with R21.
Ok, good start folks.
I'll add in the details as they come in.
Keep it simple (as can be) as my main reasoning in doing this
is to break it down for people. So far so good.
john
What other details are needed?
Quote from: R.G. on July 29, 2009, 01:57:11 PM
What other details are needed?
Well if there was to be a "technology of the BM", the tone control explanations would have not to be forgotten.
To add to R.G.'s post
The first stages gain is a combination of the open loop gain setting of the transistor (has to be lower than 15K /100) and the 470K/39K about X12 inverting feed from a 0 ohm source, a guitar is not a 0 ohm source.
so LESS than X12 inverting because of limited openloop gain and the source Z of the guitar.
If the transistor had a lot of gain like an opamp the gain would be very close to X12 inverting (ignoring the guitar Z). The input Z would be the 39K and C1 because the node that the base and 470K and and C1 would be at a virtual ground. The transistor is limited to a max of X150 by the 15k and 100 ohm (it is even less because you need to add re to the 100 ohm and re varies with current re=25/Ic, Ic is in ma). Also where in the supply range closer to sat or cutoff
The 470K and 100K are a part of the biasing. The higher the Hfe the less current thur the 470K to the collector node. The Ic (collector current set by the designer selection of resistor value and collector operation point) "splits' at the collector node some current for the bias resistors and some for the emitter The higher the Hfe the less the loading of the resistor bias string.
There is even more. A lot going on. IMO it does not lend itself to easy change this for that simple posts
What I suggest you do if you want to understand what does what. Build the first stage use a 10K as a load after C3 (crude sim of the stages load). Use a regulated supply so the voltage does not change. Measure the nodes voltages. Then use a signal gen set to triangle build a sim of the guitar because that adds to the 39K input and set to a pickup you like to the peak to peak voltage it generates. Look at the signal with a scope then change out transistors that you measured the Hfe. Then change the parts one by one maybe remove the 100 ohm emitter resistor. Take notes maybe even listen. If you change the bias resistor(s) and want the same gain the ratio needs to stay the same if they are lower value more current is shunted away From the emitter
I will build circuit or fragments to make sure I got the math right and test them with a gen and scope.
Also If you start to get this you will understand the first stage of the Crybaby like inductor whas.
Here is an idea for the guitar sim think simple, take a pickup and volume control place them in a metal box can etc for shielding feed one end of the pickup from the gen the other end to the "top" of the volume pot, ground to gen and "bottom" of the volume pot and ground of the fragment effect, wiper to input of the effect.
The tone control – really simple, just visualise this:
The signal path splits in two parallel RC filters, one is a low-pass filter (R18 & C12) the other one is a high-pass filter (C10 & R20). The potentiometer is connected between the outputs of these two filters and acts as a "fader", panning between the corresponding output of each filter. At one far end of the dial, most of the signal comes through the low-pass filter, at the other far end the signal mainly comes through the high-pass filter. In the mid-position of the dial the output signal is that of the two filter outputs combined. Usually the -3dB points of the filters are a bit different, which results into a mid-range notch.
The main question I've always had looking at the Big Muff is why there are clipping diodes in more than one stage? It seems that anything that gets clipped in the Q2 stage will be clipped even more in the Q3 stage, making the Q2 stage's clipping irrelevant.
I'll add my descriptions for the tone stack and output:
C10 and R20 act as a high pass filter - Larger caps and smaller resistors decrease the relative amount of bass on higher tone knob settings. Larger caps and larger resistors increase the output level of the filter at a given frequency.
R18 and C12 act as a low pass filter - Smaller caps and larger resistors decrease the relative amount of treble on lower tone knob settings. Smaller caps and smaller resistors increase the output level of the filter at a given frequency.
The relative fcs of the filters detemine whether the combination of the two results in a mid cut (high pass > low pass, the result for stock components), a mid pass (high pass < low pass), or neutral mids (high pass = low pass).
R19 blends the output of the filters.
C11 is a coupling cap and also acts as high-pass filter with R21.
R21 and R24 work as a voltage divider to set Vb for Q4.
Q4 provides some gain after the tone stack. Decreasing R22 or increasing R25 increases the gain of this stage.
C13 is another coupling cap and also acts as a high-pass filter with R23.
R23 is a voltage divider used to set the output level.
I posted this a long time ago and Aron used to have it archived somewhere
funny how nobody mentions this key resistor :
R12=8k2
replace by a 10k trimmer, and set to taste - it affects the overall "dirt/sensitivity" response more than anything IMO
I've woken up old BMP's by tweaking this guy alone ...
R12 does two things, mainly it allows more drive into the second clipper stage and also, to a lesser extent, slightly reshapes some of the NFB going on in each stage around it ...
eons ago I wired up a BMP with trimmers replacing every resistor except for a few obvious ones and switches with multiple caps ... as expected most of clipping occurs past a certain gain level and then doesn't really change much - that's because the diodes dominate the clipping picture - even using high gain NPN devices doesn't necessarily give you more girth to the grind ... you can get a bit more edge from the gain stages if you eliminate the emitter feedback in the gain stages (R5, R13, R16) but not that much ... my feeling is that the stock resistor and cap values were well chosen - tweak R12 and that's as good as the circuit gets IMO
in response to the doubling of clipper stages - that raises a good question ... I find the BMP's dirt is not as focused as some similar fuzzes, I think as a result ... but it is what it is - certainly serves as a design data point ...
holy crap i'm actually learning something. all these explanations are making me see the schematic completely different than i did before. thanks for starting this!
As for doubling up the clipping stages... Well, for a given amount of voltage gain (in total) it results into harder clipping than a single clipping stage would provide. Also, the signal to the second clipping stage does pass through the low-pass and high-pass filters involved, which will then alter what gets clipped in the second diode clipping stage and in what proportion. It's a complex process and the outcome depends a lot on shaping of the frequency response ("voicing") and gain / overdriving levels involved.
Think about it. If this kind of "cascading" of overdriven stages was futile all tube amps would practically have just a single gain stage.
I skipped the tone circuits because Jack's done those to death at his site. It's an overlapping blend between a single-RC high pass and low pass. Twiddling the overlap gets you a whole lot of different over/underlaps.
As to multiple clipping stages, the real story is in how hard each clipping stage is driven over and above the clipping knee. For the most interesting clipping you want the waveform driving the clipper to spend as much time in the bending-over-but-not-flat-topped part of the clipping. This is simpler to do if you have a previous clipper stage to keep things in bounds so you know where the clipping's going to go. And with more than one stage, there is plenty of gain available to get a lot of clipping.
And, as Teemuk says, and I have said for a long time, the outcome depends on the shaping of the frequency response both *before* and *after* clipping.
Quote from: MattXIV on July 29, 2009, 04:31:59 PM
The main question I've always had looking at the Big Muff is why there are clipping diodes in more than one stage? It seems that anything that gets clipped in the Q2 stage will be clipped even more in the Q3 stage, making the Q2 stage's clipping irrelevant.
The clipping in this arrangment is sometimes called "soft clipping". The diodes are a feedback loop just as in the Tube Screamer.
This is a good bit softer than diodes to ground as in the Rat, Distortion +, etc etc.
With only the first clipping stage in the BM the fuzz is fairly weak. Add in in the second clipping stage and you get the
classic BM "violin like Sustain" If you have an audio probe you can listen to the collector of the first clipping stage to hear
what one clipper stage sounds like.
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
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.
Just so you don't have to go back to page one to see the schematic.
(http://www.basicaudio.net/Big-muff-tech.jpg)
I wouldn't think that R6 does anything but set the lower limit of the
sustain knob.
I see two R6's. :icon_lol:
Quote from: R.G. on July 29, 2009, 08:19:25 PM
I see two R6's. :icon_lol:
Two R6's? Here be mojo! I was referring to the lower R6 of course.
And the upper one affects bias..
Great thread !
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
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
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 !
need more infos???
just look here: http://www.aronnelson.com/gallery/main.php/v/Gila_Crisis/Big_Muff/Big_Muff_Pdf/
Whoa
I don't think I've seen that before Gila. Really thorough and easy to understand.
--Brad
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 (http://www.diystompboxes.com/smfforum/index.php?topic=60143.0)
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.
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?
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
Can someone explain r22. Does it work the exact same as the other emitter resistors?
R22 sets the bias along with all the resistors to the right of C11.
John
QuoteRG: 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!
Quote from: bumblebee on January 03, 2010, 12:47:15 AM
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!
I have that schem somewhere i think, I've never really even looked at his schems much, not for a long time anyways.
just to clarify, I didn't accuse you to have taken that idea from Skreddy. I have never attempted to modify my triangle based muff accordingly to Skreddy's specs, but after your explanation I surely will :)
I never took it that way dude! :)
Quote from: bumblebee on January 03, 2010, 04:41:01 PM
I never took it that way dude! :)
well, English is not my mother-tongue and sometimes I cannot grasp nuances of your languange :)
however, your previous post about the boominess of triangle muff is great indeed. I'm still a little bit unsatisfied about chords sounds with my muff and now I know where I should put my hands. Thanks!
I remember of a discussion way before i started diy where guys argued about the capacitors in the triangle version.
They told that one must use ceramic caps in them. Does it really matter? (Wouldn't it sound better with film caps?i know, this is subjective)
Sigh, i must breadboard this before soldering, too many options.
Very interesting thread. I'll have to build a BMP now.
-Joe Hart
Some triangle muffs use film caps and electro's not ceramics. Some use ceramics. Some use a combo of each so no its not true! Some use .1uF caps and some use 1uF caps and some use both, there's no ONE triangle muff (nor any other muff) schematic that covers EVERY pedal. There's the official EHX schems but EHX never stuck to that real well anyways in the old days.
Big muffs, each individual pedal, are as varied as the people that use them and that is why some people (like myself) have so many and continue to build and modify them.
Quote from: quarara on January 03, 2010, 05:06:54 PM
Quote from: bumblebee on January 03, 2010, 04:41:01 PM
I never took it that way dude! :)
well, English is not my mother-tongue and sometimes I cannot grasp nuances of your languange :)
however, your previous post about the boominess of triangle muff is great indeed. I'm still a little bit unsatisfied about chords sounds with my muff and now I know where I should put my hands. Thanks!
no problem.
God damn it... I love this place. Thank you so much.
:)
Quote from: welcomb on September 28, 2009, 06:58:19 AM
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?
It happens I'm working on a Muff with active bass blend (not clean blend, bass blend) for bass. Have it up on breadboard, had it in the studio and got some major trouser flapping going. I like it so far, but I'm not done with tinkering. It should be no problem to voice the original circuit, well, "original", remove the lowpass filter from the blend driver and go from there and have a straight clean blend in there. I might influence the straight (no-blend) muff sound though - you'll have to see.
PCB V1 is done, but not verified yet. I was going to wait until I was happy with it, but I'll get it posted soon to give you some ideas.
changing c8 to .004uf will give you flat mids on the NYC reissue version.
Hi
QuoteI skipped the tone circuits because Jack's done those to death at his site. It's an overlapping blend between a single-RC high pass and low pass. Twiddling the overlap gets you a whole lot of different over/underlaps.
is 99% of the tone section story. If you SPICE the tone section, it becomes obvious that the results depend on the impedance of the next section. In the BMP, it's not very high (around 80 Kohms), so there are some differences from the theoretical mix of the two filters. Higher impedance (e.g. 1M+) would give a "pure and stiff" blend.
Also, this is one place (of very few IMO) where the tolerance in cap values can be heard. +/- 10% can change the depth of a mid scoop. Changing a value by 20 to 50% is enough to get a significantly different BMP. Which might explain some of the differences between square and triangles, colour vs bw, NY vs Moscow, etc.
I just remembered - most of these variables can be checked out using Duncan's Tone Stack Calculator (if it is still on the www)
cheers
It's hard for beginners to get and remember, but there are always two more impedances involved with any circuit fragment - the source impedance driving it and the load impedance after it. Those simply have to be considered.
Quote from: brett on August 10, 2011, 07:47:50 PM
... this is one place (of very few IMO) where the tolerance in cap values can be heard. +/- 10% can change the depth of a mid scoop. Changing a value by 20 to 50% is enough to get a significantly different BMP. Which might explain some of the differences between square and triangles, colour vs bw, NY vs Moscow, etc. ...
good point ... i've had excellent success in experimenting with C10 ( one of the capacitors in the tonestack ) ... my current favourite is a polystyrene capacitor that i had from way back when ...
here's an example from a surplus store: http://www.allelectronics.com/make-a-store/item/CS-472/4700-PF-POLYSTYRENE-CAPACITOR/1.html (http://www.allelectronics.com/make-a-store/item/CS-472/4700-PF-POLYSTYRENE-CAPACITOR/1.html) ... cheap and cheerful
IMO, this type is awesome in critical fuzz-box ( is that an oxymoron? ) filterapplications ... and they look pretty cool to boot :icon_biggrin:
Hi guys, this is an unbelievable thread! Sorry for ressurecting it, but my question is in the vein of it...
I recently built the Black Arts Pharaoh Fuzz which is a muff with some altered values. I accidentally put bc550c transistor with reversed pinout in Q1 [could not get hold of a mpsa18] and while it did hum a little more, the sound was PERFECT. It was everything I ever wanted of a fuzz pedal, I was thinking to myself gooood damn this is what I want my fuzz face to sound! [of course cleaning up the BM with your volume knob never is a particularly nice endeavor]
From a point of how things work, how could one achieve a similar response in the later stages, as with reversing the Q1 would affect them?
I don't know if this was just a happy coincidence but it sounded f-in fabulous! Since then I returned the Q1 like it should be, and while I like the sound, reversed Q1 is better.
I should note that the muff was running on a power supply. When I attempted the same with a battery [reversed Q1] all I could hear was a loud hiss, no alterations on the tone whatsoever, no distortion, nothing.
Do we think the first transistor contributes any distortion, with "typical" guitar pickups?
What about with humbuckers, say P.A.F.s?
I don't know if there's any actual clipping happening in the first stage, I would assume very little if any. But for a given set of circuit values (pick your version!), the hFE of Q1 definitely does have an effect on just how fuzzy the BMP gets. I think it might be the most critical transistor gain in the circuit, because Q2 and Q3 are limited by their clipping diodes, and Q4 is more about volume that dirt.
What thermionix said..!! :icon_wink:
"Rough" Q1 stage gain is about 12 (470k/39k) due to NFB bias configuration but, as R.G. said somewhere inside this thread, there always been 2 more impedances than "obvious" ones - In & Out impedances..
That said, you have to take into account driver(guitar) source impedance in series with input resistor (39k) resulting in lower than calculated gain..
It actually should also be taken into account lower base bias resistor and effective Collector load (Collector resistor in parallel with Q2 input stage impedance) but it should result in too complicated calculations..
(Voltage-Sunt Gain w/o & w feedback formulae, resulting in about 9.6 (calculated) or about 6.8 (simulated)..)
So, we shake hands and call Q1 stage as:
>Booster who sets the pedal input impedance, shapes the frequency response and adds "some" gain..< :icon_wink:
(ElectroSmashCopyright)