Measuring transistor voltages

[KerryF]

So I have had a multimeter for about a week now and cant really figure out how I am supposed to measure the voltages.  Can someone tell me how I am supposed to do this.

Also, I just finished building a MOSfet type of booster.  Would putting one with higher voltages in make the boost louder and add a bit more gain?  I am using BS170 MOSfets in the pedal.  The pedal does sound great and all, but if it is possible, everyone would like to have their pedal working at its possible best, so yea.

Thanks all!
Kerry

[Seljer]

connect the negative lead to ground, use the other lead to measure voltages.

I've got no idea if mosfets have any kind of gain differences. Though I don't see how a properly working boost circuit wouldn't give enough gain, the Mostfet Boost gives about 40dB of boost at max settings which should be plenty.

[KerryF]

and connecting to ground is where?  its not in the circuit.  its seperate.  i recieved a bunch of the BS170s from mouser.

i am getting more than enough boost, but i want to see if it is possible to get even more.  i read Zachary Vex's page on the Super Hard On, and he says that it uses MOSfets and that each pedal has minor differences and to play different ones to fit your gear right.  i am thinking that it may be different MOSfet voltages that alter the sounds on those pedals, so why not this one?

[markm]

Sounds as though maybe you're looking to get a little bit of "grit" out of the Mosfet Boost as opposed to Gain?
That circuit is going to be clean as a whistle for the most part. Powerful yet clean.

[Seljer]

and connecting to ground is where?  its not in the circuit.  its seperate.  i recieved a bunch of the BS170s from mouser.

i am getting more than enough boost, but i want to see if it is possible to get even more.  i read Zachary Vex's page on the Super Hard On, and he says that it uses MOSfets and that each pedal has minor differences and to play different ones to fit your gear right.  i am thinking that it may be different MOSfet voltages that alter the sounds on those pedals, so why not this one?

mostfets don't exactly have "voltages", you can't measure it with just a multimeter. Many multimeters have the ability to measure the current gain of BJTs on their own, but for other stuff you're going to have to make up a basic test circuit to determine stuff like that (theres a JFET matcher on geofex, as well as stuff on how to measure the gain and leakage of germanium transistors), no idea about mosfets, just go by ear...

[Herr Masel]

and connecting to ground is where?  its not in the circuit.  its seperate.  i recieved a bunch of the BS170s from mouser.

i am getting more than enough boost, but i want to see if it is possible to get even more.  i read Zachary Vex's page on the Super Hard On, and he says that it uses MOSfets and that each pedal has minor differences and to play different ones to fit your gear right.  i am thinking that it may be different MOSfet voltages that alter the sounds on those pedals, so why not this one?

I think you are confusing with voltage rating with actual voltage. A transistor not connected to anything doesn't have any voltage or current going through it, therefore you can't measure it. You can measure the voltage on the transistor for example in your booster, with one lead of the dmm connected to ground and the other at the point you want to measure, as Seljer explained.

Voltage rating is the maximum voltage you can pass through a component before it burns. Therefore if you have a capacitor that is supposed to see 20 volts in a certain point in a circuit you should use a capacitor with a voltage rating of at least 25-30 but the actual rating doesn't make a difference to sound I don't think.

[markm]

Voltage rating is the maximum voltage you can pass through a component before it burns. Therefore if you have a capacitor that is supposed to see 20 volts in a certain point in a circuit you should use a capacitor with a voltage rating of at least 25-30 but the actual rating doesn't make a difference to sound I don't think.

As far as I know you are correct.
Voltage rating for caps is just that.....the voltage rating. 

[KerryF]

Ok, thanks then guys.  Its working great anyway, just wanted to know.  And I said before, its a MOSfet type of boost.  Its not the Mosfet Boost pedal.  It does have grit to it also, so its all good.  Just wanted to know.

Thanks!

[R.G.]

The reason techies are so obsessive about technical terms is that the words have very specific meanings that are not always what they sound like or what common usage has perverted them to. Take "gain" for instance.

Electronic gain means just how many times bigger than the input the output is. Gain says nothing whatsoever about how much distortion you get or how much overdrive or boost you get unless you also qualify that with what amounts to the limits of the output ability of the device you're talking about. The limits are usually set by the power supply, and that's the area you're sniffing around here.

If you have your booster built and you up the power supply voltage, it usually adds no more gain at all. That is, the output is just as many times bigger than the input as it used to be. You have added the ability to make a bigger output voltage, so you MAY be able to drive whatever follows the booster harder. As many boosters are used for overdriving the input of a tube amp, that might produce more distortion. Whether that is closer to its possible best or not is only possible for you to say.

If you want more gain, you usually have to change something in the circuit that is limiting the gain of the device. Depending on the circuit, if you already have it running at its biggest gain, then more voltage won't help. You'd need more stages or a higher gain MOSFET.

There is always the question of whether more gain equals better. More gain is easy - a common opamp has a gain between a hundred thousand and ten million. So if you had a gain-of-a-million opamp powered from a 9V battery and you put a 0.1V guitar signal into it, the gain would be not 100kV, but something under 45. That's because the opamp cannot swing more than 9V peak to peak or 4.5V peak, and the resulting "gain" is 4.5V/0.1V = 45. It's really trying to do a million, but it cannot swing that big. Moreover, it's almost impossible to control that. Electrons jumping off air molecules would bang it one way or the other into the power supply and you'd get a lot of noise, maybe enough that you could not hear your signal. The thermal noise of the wires connected to it would make it noisy.

If you want to post your circuit, I'll tell you if it's already doing all it can or not. If not, I can tell you what to change to wring more gain out of it.

[markm]

And I said before, its a MOSfet type of boost.  Its not the Mosfet Boost pedal.  It does have grit to it also, so its all good.  Just wanted to know.
Thanks!

Really?
Now you've peaked my interest a bit more......got a layout or a schem 

[KerryF]

I am PMing you markm about it. 

[markm]

Got it.