Penultimate zen all mosfets distroyed

[Rixsta]

hi im new here and new to electronics but have managed to build two zen v4's

one channel works ok but has a lot of hum when a cd player or input isnt connected. While the other channel the one i bult first worked ok for about a week, but now works for minuite or two and then all the irfp044's blow, and resistor r0 goes up in smoke

this has happened twice and im wasting me money so just wondering weather you smart people here have got any clue what the problem is..

The sound was amazing compared to my bang and olufsen
http://www.beocentral.com/productinf...oductid=BM2400

With the zen v4 the kick drums in most songs seemed to be more pronounced and i tried eq ing my bang & olufsen to try and get the same sound as my zen but it just couldent do it lol.

Cheers Rixsta

[kilowattski]

There are so many possibilities. Firstly check all your wiring because you most assuredly have a grounding problem. Did you build the Zen V4 exactly as described in the PassDIY article? When you first turned the unit on did you perform the adjustments? When you keep replacing the Mosfets are you replacing them with matched pairs? This should get a dialog started so we can help you.

[till]

Did you use enough heatsink? what temperature did the FETs reach? Is mounting of FETs with grease and good contact to heatsink?

Is the amp oscillating? My Zen V4 did oscillationsat 166kHz and blew Rs. when i build it, this happened with thin cables between PS and amp and bad contacts (crocos) With good connection and thicker wire between PS and amp it workedwithout problems.

Do a search, you are not the first one.

[Rixsta]

Thanks people

first im going to check the for right voltages present, can i do this without the mosfets attached ? probably no

The circuit i built has the feedback circuit there but not connecting to the output, and im using a 15,000 output capacitor with no bypass
the mosfets are irfp044n everything else is the same as nelsons exept theres no resistor going from ground to the chassis.

im not using matched pairs but there probably not that different,
iv'e kept the mosfets the way they were when the amp was working. so i cant see heat being problem

when it works it sounds fine and only a bit of hum present and no oscilations. im using thick wire from the power supply to a prototyping board.

[Rixsta]

actualy iv'e just remembered i unplugged the input whilst the amp was on, maybee the cd player i had it conected to was prventing the problem from happening by grounding the amp properly.

[Rixsta]

heres the prototyping board

[kilowattski]

No hum when you had your cd player attached is a real good indication that you have a grounding problem. What feedback did you add to the circuit? Also make sure you included the bridge rectifier for isolation to the power supply.

[Rixsta]

Im still curently checking my amp over but have also found this site http://www.geocities.com/fuherb/sonofzen.htm

and have noticed the zener diodes
my question is can theise be used in the zen 4 for mosfet protection, also giving me the time to test my amp for the corect voltages before the mosfets blow.

if someone could show me how to add the zeners corectly i would be very pleased indeed..

[kilowattski]

My suggestion is before you go start adding stuff, get the unit working when built exactly to the schematic. Once it is working reliably, then make your modifications. The Zen 4 works very well as advertised with no modifications. It is a tried and true design and many have been built to print and worked well. Since you are a beginner I suggest you get the original design working first and learn from the experience. If you go willy nilly and start modifying before you got the original nailed you may never get it to work no matter who helps you. As a start you know there is a ground problem. If you have made any mods, remove them and lets see if we can get this thing working reliably first.

[Rixsta]

cheers for the help kilowattski and till you are most probably right so i shall post here sometime again when iv'e fixed it.

Positive thinking might just work too.