"Piggybacking" trannies for lower gain

[javacody]

Trust me, try it the way that Brett has it and I doubt you will be interested in "removing the piggyback".   :lol:

[brett]

If you replaced the emitter-bridging resistor between Q3 and Q4 in the Miss Piggy with a 25k pot, you'd have a neat "pig" or "piggy" control that'd take your gain from low to high (high now meaning maybe 50!)  At low gain I suspect you'd get softer, more transparent, organic fuzz, at mid gain you'd get a kind of "clean Germanium" sound, and at high gain you'd get a tighter, more "constricted" fuzz.  The high gain Si fuzzfaces have a reputation for sounding far too hard/tight - resulting in "congested" or "sticky" feel.

[brett]

Oops.  I forgot that the bias on Q3/Q4 will change if you change its gain with a pot.  I've noticed this effect already when using 0, 1k and 3.3k resistors in the Miss Piggy.  Each resistor needed adjustment of the collector trimmer to get back to 4.5V.  But I wonder if the bias goes "off" by an acceptable or unacceptable amount with a 10 or 25k pot?

[idlefaction]

i can tell i'm going to have to build one tonight.  did you have to do this when it's friday in new zealand?    i was going to get drunk!!!  *grin*

now for the serious stuff.  say we increase the voltage across the base-emitter of the compound device, what's happening?

i'm going to call the tx with no emitter resistance Q1 and the tx with the emitter resistor Q2.  both Q1 and Q2 have their depletion regions shrinking at the same rate since no current is flowing and it's a function of the voltage.   as soon as some current starts flowing, we have this problem of the emitter resistance.  the BE junction of Q2 and the resistor form a voltage divider - and the current develops voltage across the resistor, which in turn lowers the voltage across the BE of Q2, which thickens the depletion layer of Q2.

meanwhile, we have this voltage at both bases.  as it tries to go up, Q2's 'resistance' drops at a lower rate to Q1's, but without actually affecting the output signal...  so as we turn the compound device on more, we'd expect less and less current to go through Q2 and more and more of it to go through Q1.  you could check it by measuring the voltage across the emitter resistor on Q2, it should go up at a lower rate than the bases do.

so we in fact have a device that has a softer 'turn on' knee but looks the same once you get it turned on.

i might be way out of line but that's my thinking on it.  

[b_rogers]

so if you want to add a "oink" pot (piggyback), you better have a bias pot huh? i am gonna experiment later with some combos..

[Brett Clark]

RG - I've been thinking about the analysis/modeling issue on this. I'm expecting that, once an analysis is complete, that there will be lots of dependence on parameters that are loosely controlled (like hfe itself) or are completely unspecified (like the variation of hfe around cutoff).

If you come up with something good though, I'll be happy to see it!

Also, it may be that SPICE will give nonsense on this - many of the transistor models have a lot of approximations that are generally valid, but not for "fringe cases" like this.

[petemoore]

Take Q1 emitter to outside luf of pot [25k? to start with?]
 Take Q2 emitter to other outside lug
 take the wiper to a socketted resistor to wherever it would go [ground?]
 Then you could turn one up and the other down as it were at the same time.
 Go from the 'front' one to the 'back' one...siamese twinzistors

[petemoore]

When this thread popped throught the needle...that this concept is panning out in reality is beyond Kool IMO.
 Siamese Twansistors share the pot !!! ]?]

[Elektrojänis]

How about putting a capacitor in parallel with that resistor that is placed in between the emitters. Would that make the hfe lower on the higher frequencies? Some other weird FX?

[Doug H]

Has anyone actually compared the sound of this arrangement in a FF to a Ge FF?? This is really exciting stuff! I can't wait to try it out!

Brett and R.G., thanks for all the effort!

Doug

[Kleber AG]

   
I tried that with the easy face I built the other day 2N3906s for Q1, Q2, Q3 and Q4.

For the first gain stages i used a 2k2 emiter and for the second gain stage a 4k7 resistors.

I had the worst time trying to stop playing!!!  

Wonderful tones! No noise, easy to bias, great bass response, bell like tones!
I've just started to use Fuzzface (the easy face is my first ever) and I'm addicted to it...

Thanks for making people all around the world more happy about playing a guitar.

Kleber AG

[Gus]

Brett, R.G.

   I would think that using two of the same devices would be more consistant.  Maybe we should look at devices that have a big change if Hfe vs Ic at the current levels we are working at.

  There is an pro microphone pre that uses 8 matched transistors in the input section.  That was done for noise I believe.

  I stopped  building effects for while still draw out designs in my notebooks.  I have been busy building,modding, learning about etc. tube and transistor circuits for condenser microphones.  Look what happens one of the coolest things in years this is as much fun as the ampage time learning about the rangemaster!

Gus

[Ed Rembold]

Very cool thread guys!
you've probably designed the next generation FF!
Thanks, Ed R.

[gez]

How long till Dunlop/whoever cottons on to it?  

[javacody]

I have a Fuzz Face (dunlop reissue) that I modded with better Germaniums. The germaniums I used are OC88's (? Can't remember for sure) and are a little higher gain that I would like (100 to 120) and to me, this si Fuzz Face I just made (which is identical in every other way) sounds far better.

I would say you get Germanium sound without Germanium's headaches.

[javacody]

Yeah, I was thinking the same thing gez. I wish RG would patent it so that the big shots wouldn't get a free ride offa this.

[Doug H]

I have a Fuzz Face (dunlop reissue) that I modded with better Germaniums. The germaniums I used are OC88's (? Can't remember for sure) and are a little higher gain that I would like (100 to 120) and to me, this si Fuzz Face I just made (which is identical in every other way) sounds far better.

I would say you get Germanium sound without Germanium's headaches.

That sounds really encouraging. Just what I and a bunch of other like-minded people want to hear. :lol:  :lol:

After messing with the FT70 on the breadboard, I realized I do like the si FF sound. But then again, the lower gain transistors sounded the best. This is all very fascinating- stompbox technology history in the making!

Doug

[Doug H]

   
I tried that with the easy face I built the other day 2N3906s for Q1, Q2, Q3 and Q4.

For the first gain stages i used a 2k2 emiter and for the second gain stage a 4k7 resistors.

I will give that a try, Kleber, thanks!

I had the worst time trying to stop playing!!!  

I *hate* it when that happens... :lol:  :lol:  :lol:  :lol:


Doug[/b]

[Nasse]

http://www.freewebs.com/nassetronics/emitters.jpg


I had a dull moment this day and drawed something like this on my calendar corner at job. Sorry if someone can not see the image (my lousy "pages"), maybe pasting the address to new window helps. If not, dont worry , it is just maybe useless thingie. It is just something I thought might be something that I can test those emitter resistors (just a trimpot and a dual-ganged one, halves connected across the single pot. There may be somewhat heavy "interaction"

[aron]

This is all very fascinating- stompbox technology history in the making!

VERY VERY EXciting and I am going to try this. I am excited!!!!!!!!

OK, now U guys, please give credit if you start using these ideas.

I have always had a stock of Ge transistors, but man, not needing them will be GREAT!