Mosfets: The way to go for SS amplification?

MOSFETs have some very good properties for audio amps. Lateral MOSFETs are more thermally stable than BJTs thanks to their negative thermal coefficient. They are easier to design with too - no beta droop, no secondary breakdown, automatic current limiting, and are voltage driven. However BJTs have a much higher transconductance and thus higher linearity so they are not to be totally dismissed. Linearity is after all one of the most important properties we want and look for in audio amplification. In the (near) future however, there will be some lateral MOSFETs that will rival the best BJTs in terms of linearity, at which point I will go with a MOSFET amp.

JFETs are quite different and are not used much, if at all, in output stages. However they have excellent input impedance and low drift so are more suitable for input stages and current sourcing.

Balanced connection has nothing to do with transistors so it is definately not the only way to go.

Hope this helps. Arthur

Hi Jayme,

I wouldn't get hung up on the technical details if I were you. Yes...MOSFETS can sound great in a great design, but a poorly designed MOSFET amp can sound awful. The same is true for balanced circuitry and all other aspect of audio design. Most equipment was designed by different people with varying ideas of what music should sound like. Unfortunately, the only way to know what is "the only way to go" is to listen to different amp designs and decide for yourself.

My understanding is that generally MOSFETs have a tendency to have sweeter, warmer, even darker characteristics than other transistors. The potential downside of MOSFETs is that they can be attributed to a slightly more polite or recessed midrange.

Balanced connections seem favorable to me in my system as they appear to provide a wider range of macro-dynamics. Perhaps this perception is due to the increased voltage generally associated with balanced connections. But this may not always be the case.

-IMO

You cannot really pin them down as which is better or what's the advantage of one over another. Each have their own operating parameters and do basically the same thing in the end: amplify a signal. How they are implemented for a given topology, the skill of the designer, and overall engineering from power cord to speaker terminals will determine their perfomance. Just one cog of many in a wheel.
For example, Nelson Pass used JFET's in the Threshold "e" series, IGBT's in the Forte's and MOSFET's in the latest "X" series. All different topologies and all, IMO, one hell of a good sounding product history.