Boosting output level on a Big Muff type circuit - advice sought!

[antonis]

It might seem complicated at a first glance but after some practice you'll be able to implement it as a matter of course..

[duck_arse]

...but it's entirely possible that I may mave wildly misunderstood something...! 

don't worry about it, plenty of the us here are confused by the trolling, too.

[GibsonGM]

What I found to be FAR less complicated for my 'math-limited' head was something Paul Reid (PRR) posted maybe a decade ago (!) that I saved. I've found this helpful on a few occasions to whip up a gain stage, and hope someone else does too!    If you follow the steps as written, in order, this becomes a simple matter of 'going around the circle' and doing just a couple of basic calculations.  And it works!

Way back then, Paul wrote:

"Assume 10V supply.

We want the collector resistor dropping a lot of this. "Half" is good.

Transistor base-emitter voltage is about 1 Volt. (It will really be 0.5V-0.7V, but let's avoid tricky math.)

We need an emitter resistor to drop a voltage "not small" compared to transistor base-emitter voltage. 1V is enough.

So far we have 10V supply, collector at 5V, emitter at 1V. We have lots of room (10V-1V) to swing the collector, the output terminal. We waste only 1V in emitter bias.

Remember these relative proportions! Collector resistor and collector-emitter drop most of the available voltage. Emitter resistor voltage is smaller.

How does the emitter know to be at 1V? We force the base so that 1V appears at emitter. We already pretended the base-emitter voltage drop is 1V. Therefore the base must be forced to 1V+1V=2V.

We could use a 2V battery, but not handy; we will also eventually mix audio here and a battery would absorb audio.

We use a voltage divider. Be familiar with the concept.

Pick a collector current. Often 1mA is as good as anything.

Emitter current is the same as collector current.

Now we can pick collector and emitter resistors.

We need to pick a current to flow in the voltage divider. Too small won't force base voltage firmly enough. Too high will lead to small resistors which will absorb the signal we will add later. When you don't know better, pick divider current 1/10th of collector current. 1/10th of 1mA is 0.1mA.

Later you can add your in, out, and emitter bypass caps."

[paulbuzz]

Are you familiar with the term "stage\cascade load capacity"?

I am not, but would be interested to learn!

I would change the tonestack a lot.

Interested in your thoughts about the tonestack. As far as I can tell it's a fairly standard James layout?
My main aim for this project was a muff-style pedal with more flexible tone control.
The existing setup seems to work well for higher settings of the bass & treble controls, but aiming for a more mid-centred sound by using low settings for bass and treble loses so much level in the tonestack that additional post-tonestack make-up volume is needed; leading to my original enquiry in this thread.

Any further thoughts gratefully received!

[antonis]

plenty of the us here are confused by the trolling, too.

Trolls DO have names, don't they..?

[Dormammu]

Interested in your thoughts about the tonestack.

I would change it something like this.


c11,c16 may require 2-3 times enlargement.

[antonis]

@paulbuzz: Another chart with handy formulae for real world CE amp behaviour..
(e.g. why a CE amp with R_Collector / R_Emitter = 10/1 doesn't always - actually never - exhibit a gain of 10..)



P.S.1
I do know all those nasty          formulae seem like nightmare but, unfortunatelly, you have to mess with them if you like to understand what's happening..

P.S.2
Of course, there are numerous circuits to plagiarize, as long as you DO know what are you looking for..

[GibsonGM]

P.S.1
I do know all those nasty          formulae seem like nightmare but, unfortunatelly, you have to mess with them if you like to understand what's happening..

If one wanted to really dive in, they could write these formulae into a visual basic program or one using another language...  I gave up on them when I learned to plagiarize!!      I admire those who take the time to work with these relationships until they are well-understood.

[PRR]

http://www.vk2zay.net/calculators/transistors/commonEmitter.php

[GibsonGM]

(or just use an online calculator, but they often don't show the forumula)   

[mac]

In Antonis first schematic I would change the 2k7 with a 2k5 pot wired as in a Fuzz Face.
This will give you the right amount of dirt you want from the last stage.

mac

[antonis]

In Antonis first schematic I would change the 2k7 with a 2k5 pot wired as in a Fuzz Face.
This will give you the right amount of dirt you want from the last stage.

Quite right, Mac..

But that last stage is only for Tonestack loss recovery..
(about 12dB or so - more close to a boost rather than overdrive..)

[edvard]

At Q3, there are clipping diodes that limit the output of Q3 to around the diode voltage drop rating, but also are essential to the Muff distortion tone.  However, you can try a few things: If they are Germanium, swap in Silicon diodes.  If Silicon, remove one, remove both, or swap them for LEDs.  Easily reversed, and you just might like the tone.