Jfet, amz boost modify to OD pedal

[TimWaldvogel]

i have only tampered in op amp based circuits and i was thinking about dabbling in transistor overdrives and boosts.

i know when you are using an op amp you can achieve overdrive by placing clipping diodes in the feedback loop of the op amp, where is the feedback loop in a transistor based circuit?

here is the amz mini booster link, http://www.muzique.com/amz/mini.htm could you show me where i woult place diodes in this type or circuit? or is there something im missing about transistor based circuits?

[LucifersTrip]

I can't  give a technical answer, but I learn from some of the classics:







Os Mutantes:

[TimWaldvogel]

These all seem to be fuzz/distortion pedals. Looking for something like a Smooth overdrive. Like a TS but transistor based.
Some nice jfet design or something. I have a few j201s around and wanna work on a nice overdrive pedal

[petemoore]

  Fetzer valve article, a number of biased Jfet Fetzers may have near-cousin circuit fragments appear in...
   Also see the ROG emulator pedals.
    A Jfet to bring the guitar signal up to 'workable' level', a Jfet to distort the boosted guitar signal, more Jfets continuing to add a bit of distortion in each successive Jfet stage. Any voicing and tone controls also show likely ways to wire up an amp emulator or even do a 'schematic scramble'...dump a buncha eggs [Jfets or other] in a bowl, mix and add spice to taste.
   Two or three 'tamed' [ie clipping 'just some', not too hard] stages generally would generally fall into the associated categorical vernacular: 'smooth OD', four or five start leaning toward the nomenclature [distortion]. Pickups, settings and interpretations will vary.
   Also see any 'tube sound fuzz' derivitaves [will show CMOS chip in BOM or schematic].
   

[MikeH]

+1 on the Runoffgroove stuff.  They used to have something called the "Odie" which was a Jfet OD.

As pete said, you get overdrive or distortion from Jfets by cascading them, or hitting them with a hard signal.  How hard they get hit determines the amount of breakup.

[rockhorst]

Search for the Golden Dragon, by DragonFly. He aslo has a soundclip of it in the layouts gallery. It's basically a minibooster with some different component values. Haven't build it myself yet. I'm planning to do my take on a booster 2.5, which is 2 modded minibooster in series with a tone control (BSIAB evolved from this). No clipping diodes in either of them, but it definitely clips!

[TimWaldvogel]

so whats more the dominate character in these circuits? is it the stage pushing then jfet into overdrive? or the jfet itself? like for instance, if i used a silicon transistor booster circuit like the LBP1 (provided potential component tweaks maybe for input\output caps filters etc) and pushed a basic j201 jfet stage into overdrive. would that work? i know very little about transistors and im slowly reading into it. but i have this idea like the one i described above.c

lbp-1 basically (gain knob being a pot wired between stages to control how much it pushes the jfet stage. but im not sure what the jfet stage would look like. would it be a basic jfet input buffer that it distorted by the gain it is recieving? can someone point me in the right direction, if not a similiar circuit

[MikeH]

I don't think an LPB pushing a Jfet would sound as good.  I think it's the cumulative effect of multiple jfets that sounds nice.  LPBs are kind of heavy handed and harmonically stale - to my ears anyway.

but im not sure what the jfet stage would look like. would it be a basic jfet input buffer that it distorted by the gain it is recieving?  can someone point me in the right direction, if not a similiar circuit

Already have.  Go to runoffgroove and look at the fetzer valve article.  That will show you exactly what a jfet gain stage (not a buffer) should look like.  It will give you all the info you'll need as far as biasing, etc.  Then look at the other jfet designs - you wont find more info and jfet designs anywhere else.