Question about transistors and clipping

[Leopold T]

Hello all. My understanding is that, if you're making a fuzz or distortion pedal, a very important factor in choosing transistors is the voltage at which they start clipping. I checked out the datasheet for the BS170G (which is used in the ZVex Distortron) but I can't make head or tail of it. Having read the data sheet I still don't know the clipping voltage , and I couldn't even find out if the transistor is germanium or silicon.

Can anyone help me out here?

https://www.onsemi.com/pub/Collateral/BS170-D.PDF

[ashcat_lt]

It is my (possibly mistaken) understanding that a transistor amp stage like in a fuzz always clips at (or close enough to) the supply voltage on one end and whatever voltage the source resistor sets at the other.  Assuming, I guess, that the load is negligible compared to the drain resistor...

That is, most transistors will swing one way until they are close enough to straight wire and the other way until they are basically open circuit.  To know where it's going to clip, you look at the voltage divider it creates and figure out what happens in those conditions.

[R.G.]

Ashcat is right - the reason you can't find that on a datasheet (well, one of the reasons, anyway) is that the start of clipping is not a characteristic of the transistor itself, but how it's used in the circuit, and what power supply is provided, and the other resistors and such in the circuit. Whomever led you into believing that the clipping voltage of a transistor is important is themselves confused about this point.

Beyond that, you're not asking about a normal transistor. The BS170 is a MOSFET, not a bipolar transistor. These are two fundamentally different kinds of transistors. That will make the question even more confusing for you.

The BS170 is a silicon device. I know this because there are no germanium MOSFETs. There are some exotic transistors that are made from silicon/germanium alloys, gallium arsenide, silicon carbide, and others. But no germanium MOSFETs to my knowledge.

[Leopold T]

Thanks

[PRR]

> no germanium MOSFETs to my knowledge.

They are A Thing. For a decade researchers have been saying they will be a better thing, for some specific applications.



Mostly theory stimulations. And you are quite right that Leopold is not going to find one. (And that to first approximation, "clipping" is all about how you use it, not what it is.)