25W MOSFET amp problem :(

[Mlaen]

It's me again, ,with the same amp and simisliar problem...
I've finished constructing the amp (new one) and when I connect ampermeter in series with Q8 drain and turn it on fuses, R16, R13 and Q6,7,8,9 blows!
I have checked PCB many times but I found no errors, I don't know where to start search for mistake...
You can find the amp at http://www.electronics-lab.com/proje...001/index.html
Any help is welcome! Thanx!

[MikeB]

Maybe there is something wrong with your powersupply ?

[Mlaen]

When I messure it output is -+36V
I think PS is OK

[MikeB]

Can you post pictures of the assembled amp ?
The schematic looks fine and uncomplicated.
R10&12 also should have burned, if not, there is something
very wrong !

[richwalters]

Now the nasty ones...ehh... This isn't easy following it through without having the board in front of me-.I'm suprised there isn't a resistor somewhere in current path to Q2.....R4/R5 are they correct ? if not, then there's an unlimited current path from + to 0v. Same applies for R9/10... Q5/6.
Has R11 got badly soldered joint? Is it o/c ? Obviously check all semiconductors are the correct way round. If you do find one wrong......replace with new ones. While you are about it, just check C9 polystyrene cap for s/c......you might have branded it with the soldering iron. This wouldn't be the cause of the problem.

rich

[psychosteve]

i know it sounds silly but i had a problem similar to this,

it turned out that the amp meter i was using had a feeder circuit in line with the current sense. and it was the amp meter changing the circuit that made every thing blow. some thing about inductive windings???? dont ask me, i dont know why.

if your setting up the circuit for the first time, setting bias current?, have you used a smaller power supply, or small batterys, or put resistors inline with the power supply to make sure that the circuit is correct, before you try to sett every thing?

see you soon, steve.. ..

[psychosteve]

should quincent current, for bias setting be measured on the power line into the amp, ..... not inline with Q8????

i dont know much, but all the amps ive ever built have a fuse, and the setting is done with a amp meter in series with the fuse...

but then what do i know, see you soon, steve.. ..

[Rahul]

Hi!

My personal experiance P ch FETs are not very regular consumer components in comparison to N Ch FETs. Possibly the trouble may lie with the N ch FET alone.

Seeing you are interested in N Ch FET designs I made a single sided bord for the Pass Mod for HK Ciatation 12.

You may download the artwork from:

citation 12

It is not the ultimate but nevertheless it is a very good for price to performance ratio. The layout has been tested many times over. ( Boards were free for asking for Indians DIYers)

Regards

Rahul

[Rahul]

N ch FET alone

Kindly read it a Pch trouble . N Ch are more abundunt.

Regards

Rahul

[MikeB]

I never had any problems with P-channel hexfets from IR.