germanium-like silicon transistors

[kwtsos]

Hey everyone..

I am about to build a Tonebender pedal.. I want to use silicon transistors just for stability but I want a germanium-like sound..
Any ideas on what silicon transistors should I use?

Also, If i make it hybrid, which transistor should be germanium? I mean Q1, Q2 or Q3?

[LucifersTrip]

I am about to build a Tonebender pedal.. I want to use silicon transistors just for stability but I want a germanium-like sound..
Any ideas on what silicon transistors should I use?

I don't think any silicons can give you a ge-like sound, but you can always try to get close...you will also have to re-bias (change) the
circuit to accommodate silicon...search the forum & google for silicon MKIII /MKIV /Buzzaround for tips

for instance, if Q3 is si, I don't think you need the diode, but you'll need a large resistor (say 1M) from B to C or from B to supply (not ground)

Also, If i make it hybrid, which transistor should be germanium? I mean Q1, Q2 or Q3?

Q3

[brett]

Hi
it's a bit like asking what sort of wood is most like metal. Sure, some sorts of wod are hard and heavy and strong. But are they metal? No.

Most people concentrate on getting the hFE right. Some people add components to simulate leakage, because it's needed in some circuits to supply a base current. A few of us like to have high capacitance like the old devices (that's why Gus and I suggest power devices like TIPs and BDs).

BD139 and BD140 are fairly good (hFE 120-160), especially with an 'extra' small cap across the B-C junction. Maybe add a reverse-biased germanium diode (or a few) to simulate C-B leakage. Unfortunately, the B-E junction will always have a 0.7 V drop and not the 0.3V drop of Ge. As far as I know, there's nothing you can do about that.

Also, you might want to check out 'piggybacking'.
cheers 

[R.G.]

The next step beyond piggybacking is to add a germanium leakage diode from collector to base. This changes the leakage (but not the biasing) to be germanium-like.

A small capacitor from collector to base (start with 47pF) gets the frequency response down. It's not nonlinear like the parasitic capacitance in a germanium junction, but it'll be closer.

[mac]

I compared BD175 and BD237 with ACxxx and their high internal capacitance is close enough.
Low hfe, high capacitance, no leakage, cheap 
And they react to guitar volume like ACxxx. I think this is because they are power devices and ic=ic(ib) curve falls in a similar way.

mac

[Paul Marossy]

The next step beyond piggybacking is to add a germanium leakage diode from collector to base. This changes the leakage (but not the biasing) to be germanium-like.

A small capacitor from collector to base (start with 47pF) gets the frequency response down. It's not nonlinear like the parasitic capacitance in a germanium junction, but it'll be closer.

Great ideas. In theory, that way you can get quasi-Ge sounds with the stability of Si transistors.

[Thecomedian]

germanium sounds different from silicone due to the response coming out of saturation or cutoff, in that Si responds much sooner. This is what leads to a harsher distortion with silicone vs a more organic sounding distortion with Ge.

Also, the type of doping material used in turning Si or Ge into a Semiconductor has an effect, which is why earlier Ge's are "better sounding" than later Ge's.

You just want to produce something that causes this "laggy" response time. There's obviously a way to mimic Ge without using any Ge parts inside at all. Im thinking about what sort of circuit design could cause this.