Germaniac one stage booster (samples and questios)

[zjokka]

As I'm not a fan nor a man of thousands distortions, but will never play without a booster pedal again, last month's FX competition inspired me with to try a simple germanium booster. I hardly know what I'm doing electronically, but reading this board sort of gave me some intuitive knowledge to start experimenting.

Did want to repost it here because wanted to refrain from bumping the competition thread and I have some questions.

It's a basic simple gain stage, stripped of all unnecessary components, because I wanted to find out what makes a gains stage work with germaniums and not with silicon transistors.

I was surprised to find that it doesn't need any voltage to the base. Does it still work because the collector is leaking ("a bit" = low leakage!) a bit of current?
Also why does it get cleaner with higher bias in this setup? Is that for the same leakage reason.
If you piggyback and add a resistor a SI is the resistor simulating the leakage?

Is leakage the reason for the always lower gain of GE?

five clips way at the bottom
any comments are welcome.

thanks
zj
---------
maybe simplicity has its own reward: hence the GERMANIAC



Q1 is a low leakage Germanium NPN, I used 2SD352H with gain of hFE 115.

C1 is the input capacitor -- .022uF or 22nF would be a good starting point, but you can try values from .01 up to .1uF
C2 is the output cap - .047uF or 47n for starters, but try up to .1uF (100nF)
C3 is 47uF or higher for more extreme though less defined maximum gain. Connect the negative side to the ground.

If your base measures too low you could add a big resistor (2M to 5M) between base and collector like shown in Tim Escobedo's Boosterama.
I explicitly tried to keep the component count down as much as I could. Of course I was tempted to remove the gain pot completely, as you can clean it up alright with your guitar volume. As I am really a lover of that thin line between clean and gritty, this really is my thing.

Mods? a well chosen tone control pre or post, diodes at the end, buffers, pulldown ? Don't hesitate, try and report the results. This one's a building block, really. Simpler than the beginner project, a first lesson in biasing with simple setup, an interesting new beginner project for the modcrazy modders.

I succeeded recording a few more respresentable samples. All are recorded on a Digi 001 soundcard with a SM58 microphone in front of a BF-ed Super Reverb. Guitar used was a MIJ Strat, shielded and stargrounded, loaded with Texas Specials in neck and mid position.

The first two are recorded with the circuit as drawn, no master volume. First is a clean sample of the setup, in the second I gradually increase the gain. Did switch from Neck to Neck+Mid in the second, and had to back up the mike at almost maximum gain.

Download Germaniac Clean sample
Download Germaniac Boosting sample

Because these don't demonstrate the gain maxxed out, I recorded three more samples after installing a master volume after the effect. All samples recorded at max gain, with different Vc's. Battery was 8.8V

Download Germaniac sample bias 3.5V
Download Germaniac sample bias 4.8V
Download Germaniac sample bias 6V

You will notice that the lower bias provides more dirt than the higher values, though midway the power supply as usual would be the best choice. Maybe a tad lower rather than higher.

Because of the dead simple setup, you could put a fixed resistor in series with a pot to vary the dirt bias. But it will depend on your particular transistor what values are required.