diyAudio (
-   Solid State (
-   -   300w mos-fet amp (

raszvan 24th April 2005 03:53 PM

300w mos-fet amp
i need a mos-fet amp schematic...with pcb...
rms-aprox 300w
i can't find one...:xeye:

bigpanda 24th April 2005 04:46 PM

Did you look at AV400 by Holton

edl 24th April 2005 06:45 PM

lets bulid Quasi's great quasi-complementary design.
that gives 350W(rms) to 4ohm. of course with lower rails (and maybe a few modifications) the power will be less, so if 250-300W is enough, you can use 60-70V idle rails.

on the last page of the thread you will find the attached schematic in "pdf".
there is pcb-drawing there, too.

it's recommended to read the whole thread!


(instead irfp450 you can use the cheaper irfp240 in the output)

ezis666 25th April 2005 11:51 AM

Yes, i have tested and this is good:cool:

quasi 26th April 2005 01:48 AM

Hi Rasvan
The amp suggested by edl and ezis666 has been running now for more than a month without any issues. It is very quite when idle and very clean under power.

Last week I took it to a friends house for it's first public audition.

We ran a NAD CD player and NAD receiver as the pre-amp into the power amp driving a set of IMF transmission line speakers (very nice speakers).

Everyone was impressed with the amp and another amp will be built by the host and his son as a project.

If you decide to build it, contact me if you want any advice.


amplifierguru 26th April 2005 02:01 AM

Hi quasi.

Does your amp have a turn on thump? Have you tried to DC couple it to eliminate the electro's from the signal path?


quasi 26th April 2005 02:51 AM


Originally posted by amplifierguru
Hi quasi.

Does your amp have a turn on thump? Have you tried to DC couple it to eliminate the electro's from the signal path?


Well yes and no.

The amp boards themselves do when they are first turned on and the woofers do pop a bit.

The completed amp has speaker delay via the protection circuit and this comes in about 4 seconds after the amp is turned on so no thump is sent to the speaker.

You will note that I also a have a soft turn on cct for the powersupply and this lasts about 1.5 seconds. This means that the voltages for the amp modules rise slowly and a speaker delay is required to prevent any problems here.


amplifierguru 26th April 2005 03:21 AM

Just wondering. I used to make PA amps similar to this topology in the 70's but with complementary feedback triples using MJ15003/4. There's probably a few still floating around there they were installed in a lot of clubs and discos.

They didn't us a relay output so I dethumped the turnon by using a long RC timeconstant feed to your T7 which simulated the slow charge-up of the primitive bootstrap which never thumped.

You don't mind having electro's in the signal path?

Have you tried cascoding the input stage/ FETs instead of the bipolars? dead easy with no circuit changes just drop in.

quasi 26th April 2005 03:35 AM

The final version of the amp does not use a cascode input stage but rather a current mirror. A FET input stage would work well as you sugested and would be a "drop in" provided the FETs were rated to at least 75v. In my amp I use a 1uf MKT style capacitor for the input.


Coulomb 26th April 2005 03:49 AM

Check this thread.

All times are GMT. The time now is 11:57 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2