using Ge transistor in clean boost

[jlullo]

hey guys,
if i were to use a NPN Ge tranny in a clean boost (such as the LPB, amz mosfet boost, etc), would it be a much different sounding then sillicone?

[Meanderthal]

 What you'd wind up with is pretty much Dragonfly's Creampie... which is said to have a sound all its own.

[GibsonGM]

I'm guessing a little warmer, but not likely to be very 'clean'.  You'd have to re-bias whatever you put it into to operate within the ranges of a Ge device.  I bet it would sound really good, tho ;o) 

[Paul Perry (Frostwave)]

When you sub a Ge for a Si in a circuit, you have to at least think about the bias.
Because, Si has MUCH lower leakage, and sometimes a Si circuit will not bias properly when a Ge is put in.

[Unclerny]

I'd agree with the above and I'd say to get it to stay clean through out the volume range you won't have much total gain.  It will want to clip.

Probably sound great if used right.

UE

[jlullo]

alright, so i've been reading in the archives as much as i can about rebiasing for a Ge tranny.  I've also searched on google.  I'm still having a hard time understading it, but from what i gather, i would sub in a trimpot for the resistor running to the base of the transistor.  Then, depending on the voltage that is supposed to be at the base (using a Si tranny), i'd adjust the trimpot until i got that same voltage reading on the Ge tranny.  Is this correct?

[GibsonGM]

I think it's close, but the values of collector & emitter resistors might have to change, too!  I'd start by biasing the base, and using trims on collector & emitter pre-set to the LPB etc. values, and go from there....

[jlullo]

so you'd use trims on all 3 resistors, right?

[Meanderthal]

 This is pretty close to an LPB converted to Germanium. Maybe the resistor values and trimpot location might be of help for biasing something similar. I can't find a schematic though for some reason, but this is pretty easy to follow anyway-

http://aronnelson.com/gallery/album77/CreamPie_LAYOUT_perf_001

[jlullo]

thanks meanderthal!  i was peeping that earlier.  i'm just trying to get a better understanding of everything as well.  i'm sick of my "paint by numbers" method that i feel like i'm stuck in

[Meanderthal]

 I hear that! I hesitated to post it for that reason, it looked like you were taking the more admirable figure-it-out-yerself path...  but it ocurred to me that although it's a Dragonfly circuit, it's not in his gallery, so... it was possible to miss that.

My dim understanding of transistor biasing goes about this far- replace the resistor/resistors between 9v and the tranny with trimpots a bit larger value and twist to taste... but there are other ways I suppose...

Sorry if that ain't much help...

[jlullo]

that's actually a ton of help.  thanks dude!

[jlullo]

how would you actually sub in a trimpot with there are only two holes drilled on the circuit board for a resistor.  Just snip off the middle lead?

[Meanderthal]

 Noooo! you'll ruin the trimpot. Connect leg 1 to leg 2 to make a variable resistor, then legs 1 and 3 go where the resistor would go.

[jlullo]

ah, so you.... bend it? 

[Meanderthal]

 You can, or you can just solder a jumper wire between them. If yer trying to stuff it in the holes a resistor used to occupy, it can be tricky. If you're perfing, no problemo. If yer gonna etch your own pcb, it's best to change the layout to accomodate the trimpot. Vero... I wouldn't really know...

[jlullo]

gotcha.  thank you SO much for all of the information.

i love all of you.

[Meanderthal]

 Hey, one thing I ought to add is the primitive method of transistor biasing I use may not be everything needed to convert a Si to a Ge circuit... there's leakage and gain and all kinds of things that are gonna be different, I was just talking about adding a trimpot to an existing circuit for the option of bias adjustment. The other guys were giving better advice as far as a conversion would go, because there could be a lot more adjustment necessary for the conversion to work well!

Sorry, didn't mean to mislead you, I was more saying I don't know a whole lot about biasing in general!

[jlullo]

no, i understand!  i just went off on a tangent there for a bit