Power Mosfet stage for audio amplifier

Hi
I am designing new power stage for audio amplifier.
Dou you know what are the best complementary pair of power mosfet for audio?
I am considering hexfet /due to price and good transconductance/
for example IRF240/IRFP9240 ?
latheral are most suitable but .... for example: 2SJ201/2SK1530
thx in advance
Kris

Hi Krzysztof,

In my opinion, for best quality audio, you should use transistors that are designed for Hi-Fi audio amplifiers, and of course from a shop that you know they are original products from the brand that it's written on them, not cheap chinese junk that copy semiconductors from big companies and write on them the original company brand.

I don't know to recommend you some specific transistors, because I don't have much experience in MOS audio amplifiers.

What class of amplifier do you use in your design ?

Hi
You are right, original components are much more reliable, unfortunately MOS transistors are not popular in audio constructions... for some reasons.... Manufacturers use bipolar due to better complementary characteristics. I n my project the main idea is to linearise both transistors using additional bipolar.
When the transconductance is good enough, the class A / AB has little influence to crossover distortions
- crossing 0 volt potential. I decided to focus on linearity and not fight to much to achive very deep AB class. I built one power AB class amp /mos for current stage and tube for voltage amplification/ it works fine and the sound is real clear. I hope receive same efect using Fet and bipolar for VAS - V apm stage

The IRF240 and IRFP9240 are sometimes suggested for use in push-pull audio amps. They are certainly inexpensive and it won't hurt too much if you destroy a few while developing your circuit.

I suggest including a gate series resistor (10 to 50 ohms) RIGHT AT each MOSEFT to reduce the possibility of VHF oscillation. I've had this occur more often than not with paralleled MOSFETs and it is not fun. The 'secret' to avoiding VHF oscillation is to make a symmetrical layout and drive from the center. That is, if you parallel four MOSFETs bring the drains to one location through equal length leads (very short) and the gates, first through resistors, also to one location.

Thanks David
I've built one power amp but the power stage consists of 2 pairs latheral mosfets 2sk1058/2sj162
and there was no problems with oscilations at all. I 've some experience with hex fet and I think you are right remainding me the problem I ve forgotten the issue.
Below is the part of output stage.

Hexfets are being used more and more and they produce very good sound with very good bandwidth, ultra low distortion and deliver very high output If set up correctly i.e centre rail voltage and quiesant current You can almost literally dump them just as you can with a high quality valve amp's

Good examples of hexfet complementary pairs are as follows buz908 and buz905, IRF9540 and IRF 540 if you use these in a parallel configuration such as you might do with a good quality class AB Power transistor amplifiers you can obtain very high quality audio

They are used every day in modern hi quality top end of the range In car audio amplifiers class AB and class GH amps If memory serves me correctly I think you will find that MNFR's such as sony and mishubishi also made mosfet hi fi amplifiers which were reknown for thier ultra hi fidility quality

Examples of which can be seen at this address

http://skemarangkaian.com/mosfet-300w-audio-power-amplifiers-schematics/

http://www.bkelec.com/Modules/mf450.htm

BK electronics produce " see link above " such an amplifier which is the MF1000 series also very good comprising HEXFET output stage

Then there are also the much aclaimed falcon and eagle amplifiers which are all mosfet outpt stages as well If you would like to see decent designs that is

Hope this helps you