New mosfet amp from ESP

[B.VDBOS]

Rod Elliotts new mosfet amp P101



http://sound.westhost.com/project101.htm

[hifiZen]

Bootstrapped VAS - yuk! Use of L-mosfets in source-follower is good though. Overall, it doesn't look like anything special; I can see plenty of potential enhancements.

[paulb]

Interesting how Rod seems to have changed his mind on FETs...

[Workhorse]

I dont agree with RODE as he states that lateral type Mosfets sound good as compared to VERTICAL switching Mosfets.
I am designing N-CHANNEL MOSFETS amps using IRF mosfets and has compared them with ams using lateral mosfets.
The result is somewhat different , the lateral types doesnt drives in professional way and create more distortion than vertical counterparts!

[millwood]

it is essentially the citation 12 mosfet version. and it shouldn't be that hard to figure out component values.

Incidentially, I am breadboarding a similar design using a mosfet driving two mosfet output devices.

one trick I learnt while simulating mine is that you need to run the vas stage fairly hot (like 10ma or higher) for the irf devices I am using (540/9540). Otherwise, you may have to use a driver section (I used mje15030/15031 configured in a T) which actually improved performance considerably.

i have had great luck with bootstraps so I don't quite know why others are so sick and tired of it.

[paulb]

Originally posted by millwood
it is essentially the citation 12 mosfet version. and it shouldn't be that hard to figure out component values.

I'll have to take your word on that, it looks way different to me. One obvious difference is the complementary FET outputs.

[Fred Dieckmann]

Quite a bit of difference! Quasicomp output stages are making a bit of a comeback lately Since the N channel mosfets are better than the the P channels this might be the way to go. The mosfet Citation 12 could be redesigned with all mosfets ( Zetex and IRF) and would be a very interesting project........

[Fred Dieckmann]

Mosfet 12 Schematic.

[millwood]

what I found is that you can improve mosfet performance by increasing bias current of their drivers. because of their high gate capacitance, those devices don't behave like true "voltage-driven" devices. Instead, they will have substantial gate current, especially at high frequencies: depending on your set-up, the irf540s will have about 0.5-1ma gate current at 20khz.

so one way to improve mosfet performance is to use high driver current so that any "gate" current wouldn't have a significant impact on their drivers.

I used 40ma on the driver in my mosfet jlh, and in my mosfet citation 12, I am using 10ma for the driver (which itself is a mosfet as well).

mosfet drivers (especially medium power mosfets rated at about 1amp maximum current) do quite well. They can be run very hot (into 100-200ma if you so desire), and because of their small gate capacitance (100-150ph at most), they kind of isolate the VAS from overloading the input stage. I like them a lot.

However, they do give you higher distortion, and are a major pain in the rear to run in cfp configurations.

[Cradle22]

Hi!

Why does Rod metions time and again in his articles about this mosfet amp (I have also access to his construction site with the complete circuit), that the layout of the PCB is very important, in fact a lot more important than for all (his) other amps?

Only to boost PCB sales, or are mosfet amps more open for distortions than comparable bipolar amps?

Bye,

Arndt