Hi all, I found that adding an input buffer circuit to my darlington rangemaster guitar pedal design greatly improves impedance matching to the pickups. I am currently using the input buffer circuit from a turbo tube screamer wich is a silicon transistor.
Would there be a practical way to design an input buffer circuit using an NPN germanium transistor? Would a germanium transistor inherently have lower input impedance? Furthermore, would a JFET inherently have a higher input impedance?
Attached is the current Si buffer circuit I am using.
Would there be a practical way to design an input buffer circuit using an NPN germanium transistor? Would a germanium transistor inherently have lower input impedance? Furthermore, would a JFET inherently have a higher input impedance?
Attached is the current Si buffer circuit I am using.
Hi. I don't think germanium will work better, as germanium transistors have worse characteristics over temperature. Also this buffer amplifies only current, and input resistance depends on R2 value in your schematic. With Ge such value probably won't work, as Ge transistors have much higher leakage currents, temperature dependent. So in if you use Ge transistors, 510k value may need to be reduced, or 4V5 voltage increased, to get symmetrical output. Frequency response would be also worse. I would say old Ge devices have only one advantage over Si - lower turn on voltage, that's not actual in your case. But if you have some Ge npn nearby, why not try to swap them, just measure dc voltages first with Si and after changing to Ge, to be sure output will be in symmetry.
I do not expect this circuit to work with Ge and I know Si would be more practical as far as temp stability goes but I was wondering if there is something inherently about Ge that would give lower input impedance with a properly designed circuit.
I think yes , in some circuit configurations Ge would have lower input impedance , in example ,in common emitter ,but for buffer this will just reduce input signal and add some noise ,so just degrade signal - where's the benefit ? Input impedance depends on circuit ,on local or global feedback ,if present . In very simple circuit with maximum gain ,no feedback, input resistance is lowest, when emitter is connected to ground ,and input signal goes to base . As you probably know ,Ge measures lower ohms as Si in diode mode, this makes input resistance lower .Why you need to have lower input impedance ? You can just connect a resistor in parallel to signal source .If you thinking about making a very sensitive and very low noise preamp with Ge , that's another case .I'm not aware about low noise Ge transistors suitable for that ,but maybe bjt transistor books/catalogs can tell this ,if this was the case .