New Germanium DirtyBoost/Overdrive-use those russian transistors!-Dirty Boots OD

[rnfr]

         
       this is a dirty boost and fuzzy overdrive that i designed in order to keep on in front of my loud, clean Traynor YBA-3.  not that it doesn't sound great overdriving a small amp too!  it uses Russian GT313A transistors, but just about any germanium would probably work.  this is my attempt to make an overdrive that uses germanium transistors instead of diode clippers because i prefer the sound of the germaniums.  the diode from C to B is something that i saw in the Bazz Fuss and it really adds a nice compression and breakup to the circuit.   it started out as a kind of germanium version of the Trotsky Drive/Electra but turned into something different getting the distortion from the transistors instead of the diode clippers.  it can go from a light overdrive to a decently fuzzy tone depending on your pickups and how you have the gain boost switch set, and there is tons of volume on tap.  i hope you guys dig it. 



also- i've got vero layouts for the russian transistor version as well as one for normal germs if anyone wants one.

[earthtonesaudio]

Either you have the emitters and collectors reversed, or those transistors have some serious reverse beta. 

[rnfr]

i added a note to the schem- can't figure out how to flip em in DIYLC!  i thought they were backwards, but just got used to lookin at them like that. thanks for the catch!

anyone know how to flip them around?

[earthtonesaudio]

I've had the same problem.  Maybe we don't have the latest version...?

I usually just re-arrange the circuit but it would be nice to be able to rotate the parts around.

[rnfr]

yeah i guess i could do that, but it would be kind of "upside down" you know?  ground at the top, power rail at the bottom.  not exactly intuitive.

[Auke Haarsma]

just edit the pic in an image-manipulating program (GIMP, Photoshop etc)

[Auke Haarsma]

Well, even paint could do it



Hope this helps.

[rnfr]

thanks man! 

i don't think i have any of those programs.  would you mind takin the correction completely off the schematic?


edit: aaaaaaaaahhh... who cares!  it's correct.

[Auke Haarsma]

you're welcome. Paint comes pre-installed on pretty much any windows machine. Gimp is available on pretty much any linux-machine

And, no prob, here's the schematic without the remarks:

[rnfr]

well, i've got a mac.  it has some photo editing stuff installed, but no illustrating programs installed.   i'm sure i could find some sort of freeware.

anyone wanna breadboard this thing and give it a listen?

[Auke Haarsma]

do you have any idea of the Hfe of Q1 and Q2?

[rnfr]

well the gt313a's have some sort of internal internal resistor in them, so i'm not going to get an accurate measurement.  i would guess a low to medium hfe germanium would do the trick.  it's not supposed to be an incredibly high gain circuit.  i could try switching them out with some xistors that have a known value and try it out. 

[Auke Haarsma]

Ok, thanks. I have put it in my bookmarks. When I have some time I'll give this one a shot!

[rnfr]

right on.  good luck with the pedal board!

[Steben]

there are still issues with this schematic.
Did you build it this way?
NPN transistors work on positive power, so you need +9V, instead of -9V.
If so the electrolytic caps are to be reversed too.

[PerroGrande]

Yeah -- I think there is an issue with the schematic.

Everything seems correct except the way the emitter's arrow is drawn.  It is showing up as an NPN transistor, but the rest of the circuit looks like it is designed for a PNP...

I'm also a little concerned with the direction of the diode that biases the base...  I need to ponder on that for a bit.

However, to make the rest of the circuit make sense, all that needs to happen is the emitter arrow needs to point in and not out. 

***EDIT****  The Diode direction is okay.  It is early here and it took a little more coffee for my brain to kick into the "on" position...

[Steben]

***EDIT****  The Diode direction is okay.  It is early here and it took a little more coffee for my brain to kick into the "on" position...

No it's not. You were right the first time. The diode lets the bias current through with a positive supply.

So either:
- you reverse the electrolytic caps and take +9V = OK
- you take PNP's and reverse the diodes.

[Auke Haarsma]

I didn't pay attention to that at all. Better like this?:

[Steben]

funny,
if your circuit really works this way, it has something to do with the leakage current on germaniums, since there is no current going through the diodes to the base.
If you leave them as this, you could have a weird leakage biased fuzz. If you reverse the diodes as I hinted, you have a double PNP bazz fuss.

[PerroGrande]

I've spent a little time today looking at this circuit on a simulator...   I had to use Silicon trannies as I don't have any models for Ge transistors.

However, if the diodes are "reversed" -- i.e. like they are in the schematic, the sim. shows a working circuit if and only if the forward bias rating of the diode is less than the Vbe rating of the associated transistor...

With a silicon tranny, a schottky diode worked well -- produced a nice, distorted waveform with lots of gain.  The closer the forward bias got to the Vbe of the tranny, the more square-wave-like the output became, with less gain.

I need to think on this more, because obviously something is producing enough base current to turn on the transistor...