[kelly]

Could anyone take a stab at defining these different type of amplifier circuit designs?

MOSFET
JFET
Bi-Polar

Thanks

 

[DesBen]

I remember reading something about it in the past (I think it was on Adcom's web site), but I can't find it anymore.

The only article I found is the following:

http://www.mastersonaudio.com/features/20020501.htm

It defines a MOSFET (explains what a "FET" is), but not the others. On the other hand, it has great explanations for amplifier classes (A, AB, B, C, etc.), negative feedback, and others. Recommended.

 

[thomas]

These all refer to the type of transistor used

Bipolar- amplifies current, rather than voltage. Generally sound "fast" and detailed, but also tends to give the cold, analytic sound people associate with solid state... not very good for input stages, when used properly can be great as an output stage...

JFET and Mosfets are a different type of transitor (field effect transitor), which amplify voltage, so designs using them are similar to tube circuits. Jfets (junction-fet) use traditional silicon, while mosfets use a metal oxide semiconductor... Mosfets are known for their warm, smooth sound, but can also be noisy and lack clarity ("vieled")... Jfets have a sound inbetween mosfets and bipolars, and are commonly used on the inputs of amplifier circuits...

All of these just describe the type of transistor used, and have nothing do to with the design of the amplifer. Designs frequently use more than one type (maybe even tubes) for the best sound. Also, the topology of the amp has a huge effect on the overall sound, so it's possible to get a warm/smooth bipolar amp or a fast and analytic mosfet amp

 

[geom_tol]

Quote:

Originally posted by thomas All of these just describe the type of transistor used, and have nothing do to with the design of the amplifer. Designs frequently use more than one type (maybe even tubes) for the best sound. Also, the topology of the amp has a huge effect on the overall sound, so it's possible to get a warm/smooth bipolar amp or a fast and analytic mosfet amp

Huh? The transistors work differently, the circuit HAS to be designed for the transistor chosen.

But you are right that you can make the transistors sound different by design.

Jfets are also known for very low noise, therefor they're often used in the imput stages of amps.

 

[dparrish]

There's a pretty thorough explanation at the following site:

http://sound.westhost.com/amp-basics.htm

 

[pedxing]

The link in the previous message is handy. I had suspected many of the things it had said, but never could prove them. Good dinner time reading.

 

[Alex Nikitin]

Hi,

Quote:

Originally posted by dparrish There's a pretty thorough explanation at the following site: http://sound.westhost.com/amp-basics.htm

Just a bit of warning to all - this is a generally good information site, however there are several basic errors (not just simplifications) especially in the valve-related section. So be vigilant and do not just believe everything there

.

Alex