AMB Laboratories DIY Audio

[daniele86]

Hi guys, i have a problem with my beta22 board. I connect it on sigma22 and after few seconds i see a little smoke outside the board, in fact the heatsink were very very hot. So i close the button immediatly. I controlled the circuit and i see that the trimmer is mounted in inverse mode, with initial check up I turn it "fully counter-clockwise" so I think I made a short circuit and i put a big bias current into the mosfet, is right this my thought?
Now i must change the mosfet or can be still good? how can i see if the mosfet are broke or don't function at 100%? There may be other components damaged? How can i see it?

Thanks a lot, and sorry for my poor english.

[amb]

Check the MOSFET for internal shorts between any of its pins by measuring with a DMM in ohms mode. Also check R32, R33, R34, R35, D9 and D10.

[daniele86]

Thanks for the rapid response! I check the short circuit with the component mounted or i must unmount it? And if There isnt a short circuit i considera beta22 fully work also the mosfet?

[amb]

You can check them mounted. Whether the amp works or not cannot be determined until you power on again and go through the initial setup.

[daniele86]

Hi AMB
Thanks i see the mosfet and the other componets for the short circuit, and nothing is wrong. So i made all the step of intial setup and ALL is right! all is go like AMB inital set up!
But i put the signal inside the input, and nothing came out from the headphone, no song, no noise floor, nothing.. so what means? How can i find the problem? all is connect right..i control more and more times..

[amb]

You probably wired up the headphone jack wrong. Please post a pic showing the wiring from the boards to the jack.

[daniele86]

wow it works!
I have change the jack connector, I used a old connector, and just I change it it works!
it sound amazing! thanks AMB fore beta22 and the support!! Really a very good amp!!

[daniele86]

Sorry AMB but there is another little problem..
After about 20 minuts, there is some mosftet very hot, some hot, and the last really not very hot; so there is differences between mosfet temperature, but is this a problem?
Or is normal that there is differences between mosfet temperature?

In particular Q21, Q23 from one board is too cold..i think..

Thanks

[linux-works]

on a few of my builds, the heatsinks vary in temperature. some are very hot and some much less so, just like you say.

it could be due to very small diffs in the .47's or the transistors and so they don't all carry the same exact current. I can't think of any other reason but it always ends up that I have some that run much hotter than others, on the same board.

[daniele86]

Thanks!
so isn't a problem!
Now there is a little hiss from the right channel, and i saw it during the initial set up, with a small offset, but i think isn't a issue because now i havn't the case and the mass cable.