MOS-FET - What's It All About Then ?

[RobbieGong]

I've heard about MOS-FET in audio equipment for years but I dont actually know how it works. I know it's associated with 'quality' but how ? The japs love it in some of their top integrated amps. For example one of their amps I quite like says it has Mos-Fet transistors in the driver stages AND in the power stages. How is this good or better ?

[struth]

metal–oxide–semiconductor field-effect transistor. They were used a lot in cmos circuits. they need very little current to switch them on and deliver more current. they have 4 pins as opposed to a normal transistors 3, although usually 2 are shorted together

[hornucopia]

Valve-like sound, supposedly. My Hafler DH 200 is mosfet.

[walpurgis]

I've owned and used MOSFET (metal oxide sandwich field effect transistor) amplifiers and they can sound nice, but nothing like any valve amp I've used.

Unlike the Sony VFET amps, which certainly do achieve a sound something like a big valve amp (but not the same). They sound lovely. I'd love to get my hands on a mint TA-8650.

I owned the Hitachi HMA-7500 and the Legend P300 years ago and they were pretty decent, but not truly amazing (yes, I've used a DH200 as well).

[petrat]

The only FET amp I owned was an ATC integrated, which, needless to say, did not sound like a valve amplifier .. at all ... but was very good in its own solid state sort of way. Very transparent and dynamic, but tonally uninvolving IMO.

[Oldpinkman]

The fet (field effect transistor) was the original first transistor before the bipolar was discovered. It has 3 terminals - gate,source and drain. MOSFETs are the type usually used in audio, due to their lower noise. (There are several variants including a 4 pin dual gate MOSFET). The laugh with all this "sound like valves" malarky is that a MOSFET is the transistor in ic opamps...

[Jimbo]

Croft Series 7 use MOSFETs due to their "valve" like characteristics. In fact the Series 7 is an OTL amp using MOSFETs instead of valves. I have compared this amp to an OTL valve amp and their was very little difference:)

[cloth-ears]

If you really want to make a transistor amp sound like a valve job it’s easy. Just reduce the amount of correction in the negative feedback loop it bring distortion up, then drive the speakers through a matching transformer to reduce the damping factor by about 95%. Send the hate mail to the usual address, you’re welcome…….

[struth]

You forgot to add salt n pepper :lol:

[cloth-ears]

Oh yes, the salt and pepper :lol:

[walpurgis]

If you really want to make a transistor amp sound like a valve job it’s easy. Just reduce the amount of correction in the negative feedback loop it bring distortion up, then drive the speakers through a matching transformer to reduce the damping factor by about 95%. Send the hate mail to the usual address, you’re welcome…….

Yes. Just bung a Musical Fidelity X10-D into the mix. :)


(well it works. I've got a couple)

[The Barbarian]

Ive had a few Mosfet designs. Sugden, Linx