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Old 24th April 2005, 03:53 PM   #1
raszvan is offline raszvan  Russian Federation
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Unhappy 300w mos-fet amp

i need a mos-fet amp schematic...with pcb...
rms-aprox 300w
i can't find one...
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Old 24th April 2005, 04:46 PM   #2
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Did you look at AV400 by Holton
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Old 24th April 2005, 06:45 PM   #3
edl is offline edl  Hungary
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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.

Power amp under development

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!

Regards

(instead irfp450 you can use the cheaper irfp240 in the output)
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Old 25th April 2005, 11:51 AM   #4
ezis666 is offline ezis666  Latvia
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Yes, i have tested and this is good
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Old 26th April 2005, 01:48 AM   #5
quasi is offline quasi  Australia
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Default 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.

Cheers
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Old 26th April 2005, 02:01 AM   #6
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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?

Greg
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Old 26th April 2005, 02:51 AM   #7
quasi is offline quasi  Australia
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Quote:
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?

Greg

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.


Cheers
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Old 26th April 2005, 03:21 AM   #8
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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.
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Old 26th April 2005, 03:35 AM   #9
quasi is offline quasi  Australia
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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.

Cheers
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Old 26th April 2005, 03:49 AM   #10
Coulomb is offline Coulomb  England
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Check this thread.

Hitachi 2SK/2SJ 300 Watt Class A/B Amp Completed
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