Cascading boosters Experiences?

[Toney]

Hi,
I started out just thinking of doing a dual boost pedal, spend a little time considering the swotching options but now I'm curious about results when cascading boosters.

Hairyandy reported excellent results running a modifed RM into a mosfet boost.

Search shows two standard mosfets boosts seems to get mixed results.

What has worked for you? What have you tried?

[petemoore]

  Looking at the BSIAB's, is it essentially two Mu Amp gain stages...of course with some attenuation/voicing options. Very popular, intense distortion available.
  Looking at ROG amp 'em's, cascading gain stages..."Fetzer Valve' exactly can be seen in some of them, these contain Fet stages cascaded.
  Any of the above, and Mos stages, or even Bipolar's or OA's can be cascaded to provide different types of Distortion.
 

[WGTP]

Joe Davidson's Mosfet Obsidian is essentially 3 Mosfet boosters in series.   

[Mark Hammer]

Using two boosters in a row entails some risk. 

Why?

Well consider first why you use a "clean" booster.  Usually, we use it to keep more of the top and bottom end in our signal; i.e., "clean" = more bandwidth.

Okay, now consider what people want from overdrive.  Usually it's more "smooth" and "warm" and less "fizzy" and "brittle".

Okay, now ask yourself what happens when you take a bright, crisp and hot output, and feed it to a second device that aims to keep as much bandwidth as possible and has insufficient headroom to amplify that input signal that much.  The odds are pretty good that you may end up generating harmonics of the top end, which may well increase the "brittleness" factor considerably.

Again, I'm not promising you that it will always do this, and I'm not suggesting that cascaded boosters are a bad thing.  Obviously, there are many commercial examples of the cascaded booster arrangement that have earned our collective respect.  There IS a risk, though, and I would strongly suggest that any attempt to stick one booster into another be accompanied by some modest form of bandwidth control in order to prevent the dreaded harmonics-of-harmonics.

That bandwidth control could consist of many different things, such as a simple Rat-style lowpass fiter, a cap to ground on the first and/or second pedal's input, a feedback cap, or anything else that works in similar fashion.  Essentially anything that assures that the second pedal will spend more of its energy/effort boosting lower order harmonics and not higher order ones.  Alternatively, include something on the final output to tame the fizzies.

For whatever reasons, the Ge-based boosters like the Rangemaster, even though they are ostensibly "treble boosters" probably have less upper top-end than a number of other clean booster designs, so they present less of a problem.

[phaeton]

For whatever reasons, the Ge-based boosters like the Rangemaster, even though they are ostensibly "treble boosters" probably have less upper top-end than a number of other clean booster designs, so they present less of a problem.

And probably less gain overall too.



What have I tried?  A lot of stuff.  fetzers into fetzers, fetzers into fetzers into fetzers,  lpb-2s into fetzers, lpb-2 into lpb-2,  muffers into muffers, 741s into TL082s, 4558s into 4558s, 9v powered boost stage into a 3v powered boost stage, misc. other transistor stages, etc.

Just like Mark said, you've got to be careful.  That schematic I've linked above goes between sounding awesome to sounding like deep fried dog poo to whistling dixie so loud it could saw a tree in half at thirty paces.  It's a very crude setup and therefore is very unstable and unpredictable.  Your main points of interest are going to be filtering (like Mark says) and stopping oscillations.  Some of the tricks for stopping oscillations are capacitors to ground, isolating grounds between stages, routing of circuits/shortening traces and wires, and adding a unity gain stage at the end to throw the output 180 degrees out of phase from the input (unless you already have an odd number of stages).

But fear not, brave knight!  Fire up thyne breadboard and go to town!  Post back what you find! 

[JHS]

The "Insane Gain" is nothing but 3 cascaded LPB-1 and the "Super Duper"  2 cascaded SHO, so feel free to try other combinations.
It's allways fun testing those weird things on stage.

JHS

[petemoore]

  quote of me
  of course with some attenuation/voicing options.
  I would strongly suggest that any attempt to stick one booster into another be accompanied by some modest form of bandwidth control in order to prevent the dreaded harmonics-of-harmonics....M.H.
  One way I've found among the many...is solder a little wire to ground, run a couple little caps off of it [something very small value and something small], then attach the other end of the cap at the input of the first stage, second stage...etc. noting what is heard, then try the other cap...etc.
  The just stick a .001uf or so from input to ground and repeat the LP filter applications as above to later stages.
  Voicing/trying out/revoicing...at higher volumes...'what amp', settings etc. have alot to do with what is done with the 'product' of the effect. What pickup also.
  Multi-pole LP, and other types of filters can be a nice option to try.

[Mark Hammer]

   One way I've found among the many...is solder a little wire to ground, run a couple little caps off of it [something very small value and something small], then attach the other end of the cap at the input of the first stage, second stage...etc. noting what is heard, then try the other cap...etc.
  The just stick a .001uf or so from input to ground and repeat the LP filter applications as above to later stages.

Yeah, that's pretty much all I was talking about.  It doesn't have to be complicated or extreme.  All it has to be is "just enough".

[Toney]

Ok, so once the gain stages are sorted, it's all about voicing, both in/out and between stages to humanize it....hmmm.. holy interstage harmonic amplification.............to the breadboard, Robin.

I 'm curious about driving a single Minibooster into break up using a mosfet also... I've posted  first crude attempt ideas in another thread... any help or input would be much appreciated there too.

[gaussmarkov]

I 'm curious about driving a single Minibooster into break up using a mosfet also... I've posted  first crude attempt ideas in another thread... any help or input would be much appreciated there too.

you are not alone ... 

My preference is a Mosfet Booster driving a Mini-Booster.

regards, Jack

[kvb]

I've tried lpb-1 into fetzer valve and vice-versa. Mosfet into fetzer, mini into fetzer . . .

The sound that seemed usable - and not completely out of wack - was a mosfet booster, with the AMZ tone control set to treble, feeding the mini booster. So a treble boosted mini gets my vote.  I remember thinking "I've heard this sound before . . " Very nice.

[petemoore]

  I like to find a Booster I want boxed, box it, then build other booster boards for testouts on my testjig [a tray with in/out/gnd clips to jacks] so I can re-arrange the order of the chain, and easily [with the 3 testclips and a battery] change one of the circuits out for another 'plain' [board only] one.
  I have a 'spare' gnd wire on the testjig, for clipping the DMM or a cap..whatever to.