switching transisters in a circuit with a dpdt?

[Narcosynthesis]

would i be able to switch between two transistors in a circuit using a dpdt switch? it would be easy enough to switch two of the contacts on the board to two different transistors, but would it work to leave one of the connections on the transistor wired all the time?

like leaving the collectors connected all the time, if the base isnt connected it wouldnt be able to conduct, so shouldnt affect the circuit, right?

so would this work, and what connetions should/shouldnt i switch?

David

[davebungo]

OK in theory, but have you considered that different transistors may require different bias adjustment (depending on the circuit)?  I would have thought it was only worth doing this if the transistors were sufficiently different to produce a marked change in sound (in which case they probably will have differing bias requirements).

[Narcosynthesis]

OK in theory, but have you considered that different transistors may require different bias adjustment (depending on the circuit)?  I would have thought it was only worth doing this if the transistors were sufficiently different to produce a marked change in sound (in which case they probably will have differing bias requirements).

the circuit is very simple, so i am not sure how much adjustement it would get



that is the circuit, theres only the one resistor controlling the voltage into the transistor, if you were switching the collecter you could also switch the resister at the top to suit the transistor if it need it

David

[Narcosynthesis]

any ideas anyone?

[eliktronik]

I've come across circuits that use a mosfet to act like a switch while studying sampling. Does anyone know if something like the following would work, provided we could choose a mosfet so as to minimize the drain to source voltage... Vg would be set high to allow the signal through, and set low to turn the transistor off. More importantly, how would this affect the sound of the signal?

(Note: omit the capacitor and the second opamp, as they were used to perform the "hold" of "sample and hold".)

[Narcosynthesis]

I've come across circuits that use a mosfet to act like a switch while studying sampling. Does anyone know if something like the following would work, provided we could choose a mosfet so as to minimize the drain to source voltage... Vg would be set high to allow the signal through, and set low to turn the transistor off. More importantly, how would this affect the sound of the signal?

(Note: omit the capacitor and the second opamp, as they were used to perform the "hold" of "sample and hold".)

i am not sure how that would fit into what i am wanting to do...


basically i want to know if i could leave one of the legs of the transistor connected all the time, and switch the other two between the two transistors without any negative effects (includine the bias resister at the top if needed)

David

[eliktronik]

i am not sure how that would fit into what i am wanting to do...

Heh, sorry I quickly scanned your post and was thinking more in general about signal switching.

If you don't need an LED, you could switch the signal between two different transistors with a DPDT switch. I would use two seperate BJTs complete with a diode and a collector resistor going to Vcc. Then you could use a dpdt to toggle the B,C connections of the two transistors to the circuit.

Just my two cents.

[Narcosynthesis]

i noticed now i wont be able to switch the bias resister along with the transistor using a dpdt, so the best bet would be two transistors that suit the circuit as is

but does anyone know the answer to my origonal question, would leaving one of the connections on the two transistors connected at all times while the other two are switched cause any negative effects on the circuit? as i would like to use a dpdt switch to choose between two different transistors. like would leaving the base wired pemanantly mean that it woudl use up some of hte signal switching it even if there is no supply to it from the collector? or would leaving the emitter connected add noise somehow?

David

[davebungo]

It should be OK to leave one leg connected.  No current can flow in or out of the device (ignoring any RF pick-up).

[eliktronik]

Well, something like the following would allow the transistors to be biased independently. In this case, the transistor that is switched out can't turn on because the base is disconnected. Hence, there would be no effect on the performance of your circuit.