Germanium Buffer Impedance

[Davebassman]

Hello,

I've a lot of OC1045 GE transistors, with a very low leakage and low gain ( 20 - 30 hfe ). I've searched what to do with these transistors, and I found an article from AMZ that explains what to do with high leakage transistors.

AMZ Germanium Transistor Buffer

But I think I need to rise R4 with the OC1045.

Zin = ( B + 1 ) x R4

Supposly that I have some AC128 with 100 hfe:

Zin = ( 100 +1 ) x 10000 = 1M

but for the OC1045 with 20 hfe:

Zin = ( 20 +1 ) x 10000 = 210K

It's a bit low impedance for a buffer no?

I'm wrong?

please correct me if it's wrong.

Anybody help me to calculate the Zout?

Thanks.

[SoulFetish]

Hello,

I've a lot of OC1045 GE transistors, with a very low leakage and low gain ( 20 - 30 hfe ). I've searched what to do with these transistors, and I found an article from AMZ that explains what to do with high leakage transistors.

AMZ Germanium Transistor Buffer

But I think I need to rise R4 with the OC1045.

Zin = ( B + 1 ) x R4

Supposly that I have some AC128 with 100 hfe:

Zin = ( 100 +1 ) x 10000 = 1M

but for the OC1045 with 20 hfe:

Zin = ( 20 +1 ) x 10000 = 210K

It's a bit low impedance for a buffer no?

I'm wrong?

please correct me if it's wrong.

Anybody help me to calculate the Zout?

Thanks.

If those low gain germaniums have low leakage, then you may be interested in using them as a darlington pair.


Where the gain of Q1 is multiplied by the gain of Q2, and the input impedance is extremely high (usually in the MΩ).
(But a quick search should yield the info you need to calculate it if needed.)

[mozz]

Think you multiply the noise also. Here is a good read on the darlington setup.
http://diy.smallbearelec.com/HowTos/...lingtonFFs.htm

[Helmholtz]

It's a bit low impedance for a buffer no?

Yes. I assume R4 means the emitter resistor?

Anybody help me to calculate the Zout?

Zout depends on the circuit. It's always lower than the value of the emitter resistor.

Can you post a link to the AMZ article?

[Davebassman]

Can you post a link to the AMZ article?[/QUOTE]


http://www.muzique.com/tech/ge_buff.htm

I think that this transistors aren't a good idea for a buffer.

[Helmholtz]

Can you post a link to the AMZ article?

http://www.muzique.com/tech/ge_buff.htm

I think that this transistors aren't a good idea for a buffer.[/QUOTE]

The AMZ circuit with R2 = R3 = 220K has an input impedance below 110K, the modified version with R2 = R3 = 470k has an input impedance below 235k.
A good buffer should have an input impedance >= 500k to not unneccessarily damp the PU's resonance.
I would prefer a high Hfe (around 500) Si transistor or a Jfet. The emitter follower circuit in a Tube Screamer works great.

[Davebassman]

Yes,

I agree. I only was experiment with some transistors, and what to do with this ones low gain. But definitely I prefer an opamp buffer or jfet.

Maybe I use them for a Range Master or Fuzz with darlington pair, it's a better idea I think.

[Davebassman]

Or the mystical "Harmonic Porculator".