zen v4 is kiling me!!

hi everybody. again.. this is the most blew up amp I ever had or buid, aleph 5 had never such a problems.. today I blew 15 irfp 240..

all voltages seems ok (variuos about 3-4%) except voltage across r1 I must get 0,66v and getting 1,1 v drain of q1 is 18-19v. after 5-15minutes of listening amp blows. I measure temperature and this I found- directly onb mosfets 150-160 celsius. o coldest place on hetasinks 60. heatsinks are pretty big and even with smallers heatsinks zen v 4 worked well.. could anybody say where is a problem??
:bawling:
 

Netlist

diyAudio Moderator Emeritus
2003-01-18 9:50 am
elviukai said:
today I blew 15 irfp 240..
And a few weeks ago about 30 :bigeyes: . Don't assume the amp will fix itself by putting in new mosfets time and time again. I think the 1.1V on the source resistors is too high. Try lowering the bias as much as possible, and keep the DMM in place to monitor. With very low bias the amp will play, just not as good as with high bias.
Then, when all is stable after a few hours, slowly increase the bias to 0.6V over the source R's.

/Hugo :)
 

Orgonom

Member
2001-10-18 12:22 pm
Hi elviukai,
you should check R6, Q3.

Under normal conditions it is imposible to get more then 0,7V
across R1/R0!!
Q3 regulate Q2.

Check voltage across gate - source from Q2. Should be close to 4V.
Your situation reflects that max current is only limited by R1/R0!

Hope this helps.

Andreas
 
elviukai said:
I measure temperature and this I found- directly onb mosfets 150-160 celsius. o coldest place on hetasinks 60. heatsinks are pretty big and even with smallers heatsinks zen v 4 worked well.. could anybody say where is a problem??
:bawling:


Magura said:
One thing that came to mind is that you have a heat transfer problem from the FET to the heatsink. Are you using mica and paste or ????

Magura :)




I hate to repeat myself, but if you have a temperature difference of 100C from the fet to the heatsink.......it ought to ring a bell.

Magura :)
 
thanks guys for help. as for heatsinks it wories me a little to.. as usualay I use thermal silicon(?) pads.. the hetsinks itself is ok but temperature is very high. I measure mosfets directly on its metal surface and find folowing q1- 175 C', q2 140 C", q3 100C".. measuring direcly on plastic surface of fets temperature is lower of course. heatsink itself measures 70-80 c"..as for npn I always using original ztx 450 and I read voltage from coret pin.. 0.62v.


yesterday I palyed amp for 30 minutes and it didint blow, but temeperature reached 180 C" of q1.. I adjust so that q1 drain voltage is 27v and r1/0 is 0.9v.. when I increasing/decreasing the goes miror- one increses,other decreases. so I found optimal for both. but this is not soliution I think.. :(
 
Smokin Fets n zen v4

Your problem sounds very familiar. While I agree that 100C diff between fet and sink is high, I am willing to bet that the problem is deeper. You describe the same problem I had in that once the bias was set it would play for 15-20 minutes and then poof. Take a deep breath, get rid of all pre thoughts and check the orientation of q3. I made my own boards and in the design of the q3 part got top down vs. bottom up mixed up. Found the problem by watching the voltage across r1/r0. (use aligator clips ) As the amp warmed up the voltage (hense bias) started to increase. The voltage across r1/r0 should be stable with respect to operating temp.

I hope that this helps

Scott


0.9 V accross r1/r0 is way too high.