Adding more gain to a Box of Rock

[GrooveChampion]

Hey guys, I used the complete Box of Rock schematic that's featured here and I wanted to know, is there a way to squeeze out more gain out of it?

[Frank_NH]

Try replacing the 180R source resistor for the second MOSFET with a lower value (e.g. 51R or even 10R).  That should bump up the gain.

[GrooveChampion]

OK, here's where my interest in the science of this stuff kicks in. From what I saw in the in the layout the gain control goes into said 180R resistor and into the source of the mosfet. Now explain this to me on a scientific level, if possible.

Like, can I do this with every pedal? Or atleast with most FET based drives?

[Frank_NH]

The schematic for the Box of Rock is shown below.  The BS170 is an n-channel MOSFET (and works differently than a JFET like the J201).  A MOSFET like the BS170 used in the B.O.R. is an enhancement mode device, i.e. current doesn't start flowing until the gate voltage - the source voltage (Vgs) is greater than a threshold voltage (Vth) which is device dependent.  Basically as you drop the source resistance, the source voltage drops and Vgs > Vth and the device turns on.  As the source resistance drops, the gain increases.  Another way to achieve this in a frequency-dependent way is to bypass the source resistor with a capacitor.  Note that you have to bias the gate and add the diode for protection.

Also note that you could also lower the 330R resistor and increase the gain of the third stage.  If you really want to play around with this to your heart's content, get a breadboard and set up the circuit so you can plug in different source resistances.  Have fun!  

More here:

http://www.electronics-tutorials.ws/amplifier/mosfet-amplifier.html

[GrooveChampion]

Wow man, thats exactly what I wanted. So each MOSFET is a gain stage that builds up distortion? And I suppose the S.H.O. is basically a switchable 4th gain stage?

[Frank_NH]

Yes, the gain stages are not unlike a tube amp preamp.  You can mod the stages to control gain and frequency reponse.  Again, using a breadboard you can play around with all areas of the circuit, including the tone stack.

[Sphere80]

Add the gain boost from the DistorTRON.  Jumper the 330R on the  3rd stage. Some of the earlier replies cover it, but compare the schematics.

If you like the gain stage idea here, try the Box of Metal. 5 of them!

[nocentelli]

1 x SHO = SHO
2 x SHO = Super duper 2-in-1
3 x SHO + BMP ts = Distortron
3 x SHO + BMP ts + SHO output boost = BoR
5 x SHO + FMV ts = BoM
(SHO + Escobedo tripple fuzz) x 2 = machine

Zvex gets a lot of mileage out of that boost stage.
If you want more dirt, I would simply build the stock BOR, but use a "order juggler" toggle switch as well as the bypass footswitch for the boost SHO: That way you could have stock BoR with optional output boost, or Distortron with optional input gain boost.

[Frank_NH]

Here's my take on the Box of Rock / Distortron:  A modded Madbean Boomstick.  It sounds pretty good to my ears.

http://guitar-fx-layouts.42897.x6.nabble.com/Madbean-s-Boomstick-tp29335.html

[GrooveChampion]

Whats a BMP and a FMV?

[rocket88]

BMP - big muff pi
FMV - Fender/Marshall/Vox