is it just me, or do fet based overdrives not like to be pushed?

[ode2no1]

over the years i've played thru dozens and dozens of dirt pedals, but until i built a blue magic last year i'd never played one that was fet based. i have to admit, i wasn't completely in love with it, but i did think it sounded good and figured i could incorporate it into my rig seeing as how i cascade dirt pedals anyway to where when i'm at my most distorted usable rhythm guitar sound i'll have 3 or 4 pedals on. what i noticed though was that i couldn't hit the blue magic with anything loud or it would become very congested sounding and not actually get louder, just mushier, whereas my other overdrives can be slammed and will get louder and more distorted without losing all of their own character. i ended up setting it aside, hoping a friend would need an overdrive one day and maybe make more use of it than i would. fast forward to a few weeks ago and i build up a peppermill just for kicks, knowing full well that i don't really need another overdrive...but hey, i'm bored and it's a simple circuit. so i get it all built up and actually love the way it sounds before my red snapper. what i did notice though was that again, if i try to hit the peppermill, which is also fet based, with any real sort of boost it starts to sound congested and wont pass any of the characteristics of the pedal running into it. where it's at in my chain and the fact that it's a bit more transparent than the blue magic allows me to be happy enough with it to keep it on my board, but i'm just wondering if this is something inherent to fet based overdrives so that i don't waste my time with them in the future (due to my cascading setup, that is).

[newfish]

Good question.

I've done similar cascading with OD / Fuzz boxes, and this is what I've found.

Booster into a Fuzz Face works really well.

Booster into a Big Muff works up to a point, but sounds really constricted with the booster anywhere above 12 o'clock.

Fuzz Face into a Big Muff is good, again up to a point, where the constriction comes into play again.

Booster into Fuzz face into Big Muff was just too damn filthy to tell what was really happening, but it was lots of fun.

I'm guessing that pushing too high a signal into *any* active device - which needs to have room to move in order to amplify - will seriously limit how effective an amplifier that active device can be.

Could your FET based OD be run on a higher voltage? 

Looking at things like the Dr.Boogie schematic, there are fairly high value (100s of K Ohm) resistors between each gain stage.
My take on this is that the clipping from the previous stage (the shape of the signal) is maintained, but this large value resistor limits the amount of signal (amplitude) going into the next stage - allowing the new stage to amplify the already clipped signal - resulting in yet more clipping.

There's probably something in the way that FET pedals are biased to work at their best with a small signal - such as that from a guitar's pickup - something several hundreds (or even thousands) of times greater.

[merlinb]

I suspect you are hearing the result of blocking distortion, which happens when an AC-coupled transistor or valve is overdriven to the point where the gate tries to go more positive than the source. This causes the bias to shift more negative, and generally makes for a nasty, mushy overdriven sound.
I suspect the peppermill is very susceptible to to this as it has no gate stopper on the JFET.

[caress]

I suspect you are hearing the result of blocking distortion, which happens when an AC-coupled transistor or valve is overdriven to the point where the gate tries to go more positive than the source. This causes the bias to shift more negative, and generally makes for a nasty, mushy overdriven sound.
I suspect the peppermill is very susceptible to to this as it has no gate stopper on the JFET.

what value gate stopper would be appropriate here?
perhaps you're hearing the mosfet start to clip?

[merlinb]

what value gate stopper would be appropriate here?

Something between 100k and 1Meg I would think.

[liquids]

It's hard to say.  I tried a big clean op amp booster into a Jfet mu-amp thing one time.  Seemed to drive it crazy, tonally, after a certain point.  Might be what Merlin mentioned.

However, generally speaking,  I like the sound of jfet mu-amps slamming into a a jfet mu-amp....?

I think to some degree, like tubes, there has to be a level of  signal-->clip--->attenuate--->clip--->attenuate etc.  That usually sounds good, with some filtering.  

Don't forget the filtering.

[jcgss77]

Is the boost NPN based or FET, and is it before the distortion chain or after?  If you haven't tried putting the boost after the FET distortion, I would give it a wack.  Just thinking aloud.  If I remember correctly, I think that in the thread of deadastronaut's 386 & J201 distortion someone tried NPN's in it and it didn't sound good.  Maybe there are certain transistors FET's don't like to play with?

[ode2no1]

i was running a SHO into the peppermill when i noticed the mushy overdrive recently, but i was using an op-amp based overdrive before the blue magic a while back and got the same results. the peppermill is the first overdrive that comes up in my chain now so it doesn't have any dirt running into it, and when i was hitting it with the SHO i was just messing around...not something that i actually do on a regular basis. but i'm assuming that if i put it second in my chain of overdrives i'd get the same results i had with the blue magic. i can run anything into my red snapper...boost, fuzz, overdrive, whatever...and it pretty much acts like an overdriven tube amp. it get's louder to a point then compresses a bit, smooths out whatever fuzz is hitting it. i just figured an fet circuit would behave the same way, but like i said, very little experience with them.