What Is A Mosfet Amp?

[toquemon]

I`ve been reading some posts about Pioneer Elite receivers that use MOSFET amplification and i want to know what is MOSFET and what are the differences between a normal amp. (normal amp, aka "no tubes"). I found some information but is very technical to me. Something like pros and cons of using MOSFET

 

[Polkfan]

This may help.

http://encyclobeamia.solarbotics.net/articles/mosfet.html

http://ece-www.colorado.edu/~bart/book/mosintro.htm

The real question is does a MOSFET amplifier sound different than a standard transistor amp? That is debatable. I've heard that the
Elite receivers from Pioneer tend to sound much warmer than their standard transistor competitors. I have also heard that there is no audible difference between the two.

 

[Polkfan]

Also, I think a standard transistor is a FET (Field Effect).

 

[mtrycrafts]

This may help.

http://encyclobeamia.solarbotics.net/articles/mosfet.html

http://ece-www.colorado.edu/~bart/book/mosintro.htm

The real question is does a MOSFET amplifier sound different than a standard transistor amp? That is debatable. I've heard that the
Elite receivers from Pioneer tend to sound much warmer than their standard transistor competitors. I have also heard that there is no audible difference between the two.

I guess I have to cite one too

"Topological Analysis of Consumer Audio Electronics: Another Approach to Show that Modern Audio Electronics are Acoustically Transparent", Rich, David and Aczel, Peter, 99 AES Convention, 1995, Print #4053.

David Rich examined topologies in amps over the years in his tech eval at The Audio Critic. I am sure he analized the MOSFET, I don't remeber now.

Also, if they sound warm, that would show up in the frequency response.

 

[JoeE SP9]

MOSFET means metal oxide silicon field effect transistor. MOSFET's are usually used in the output stage of a power amplifier. Most small signal transistors are bi-polar transistors. The bi-polar transistor is also used in the output stage of power amplifiers. If the amp is not described as a mosfet or fet amplifier you can assume that it uses bi-polar transistors in the output stages. There are several transistors that are in the fet family HEXFET's and MOSFET's are two of the more popular types in use. According to some MOSFET's are more tube like in their operating characteristics. Some say that they produce a veiling that has been called the MOSFET mist. IMHO the type of transistor used in the output stage is irrelevent. The result is all that matters.

 

[Francious70]

Just about all normal car audio components use MOSFET amps. Your only two choices are MOSFET and tube amps, and tube amps are HARD to find. So if you've ever heard a car stereo, stock or aftermarket, you've heard a MOSFET amp.

Paul

 

[Rip Van Woofer]

According to my basic electronics book, MOSFETs are more "rugged and reliable" than bipolar transistors, and can make for a "simpler, more temperature stable" circuit. Hence their popularity for car audio, I suppose.

The Aczel and Rich paper that mtrycrafts cites (I am familiar with the simplified version that appeared in The Audio Critic) says that it is harder to make a really low distortion MOSFET amp, for various technical reasons that frankly I do not understand. Also according to Aczel and Rich, the often made claim that they sound like tubes because they allegedly operate on some of the same electrical principles is an oversimplification. But all this gets us into technogeek territory!

Basically, I think JoeE is right: it's irrelevant as long as the implementation is competent. To risk some oversimplification of my own, using MOSFETs is a tradeoff...just like every other engineering solution to a problem. Manufacturers who play up the use of MOSFETs are just indulging some audiophiles' prejudices and bandying technical jargon about for marketing purposes.

And no, you don't have to use a bipolar transistor amp with bipolar speakers...

 

[Yamahaluver]

My MOSFET amp's distortion figure is around 0.005%, dont think that is that bad, also one of the reasons MOSFET is considered safe is because of their current limiting ability, unlike bi-polars which start passing high levels of current, MOSFETs self limit.

 

[Rip Van Woofer]

I said it's harder to design a really low distortion MOSFET amp, not impossible! I should have also said that in a well-designed amp the distortion is below the point where it's audible in either case.

 

[Unregistered]

Mosfet Vs Bipolar

The real problem is listening to a Mosfet amp when you have bipolar personality disorder. This is to be avoided!

But seriously, folks; I'm a propeller-head who designs fire detection circuits all day, and the "efficiency" of Mosfets is realized in power supplies and switches, not class A or AB analog output stages. Most output stages use Bipolar Junction Transistors (BJT's) because the circuit design is more straightforward and Mosfets would provide no advantage.

Any well designed amplifier should be transparent, be it tube, solid state, or bailing wire and rock salt. Electrons don't care where they've been...

 

[Votrax]

Propeller head is right. Most amps still use bipolar transistors. MOSFET's real work is done as a switch since they have very low resistance between the drain and source, therefore when saturated they dissipate very little heat. Since amplifiers operate in the linear region MOSFET's don't have that great of an edge over BJT's when it comes to power dissipation if designed correctly. Another great device is the IGBT. It has an isolated gate like a MOSFET, but the collector to emitter characteristic of a BJT. MOSFET's and IGBT's are more popular in high frequency/power applications such as switching power supplies.

 

[mtrycrafts]

The real problem is listening to a Mosfet amp when you have bipolar personality disorder. This is to be avoided!

I think you hit the nail on the head


Any well designed amplifier should be transparent, be it tube, solid state, or bailing wire and rock salt. Electrons don't care where they've been...

You said it again. That's two

 

[Unregistered]

stereotype amplifier

hello there!
we had a project on our electronics subject.. to construct an amplifier... we decided to use a 15watts stereotype amplifier as our project as our project... the problem is,,, we need to do some report about it.. I want to have some imformation about amplifier, how it function and any information could you give about it... thnx! it will help a lot...

 

[Unregistered]

Here is a good overview: http://rocketroberts.com/audio.htm. Click on the link 'Amplifier Power Fundamentals.

Google is your friend. Search and you will find all the info on amplifiers you would ever want.