zen v4 is kiling me!!

[elviukai]

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??

[Magura]

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

[Netlist]

Originally posted by elviukai
today I blew 15 irfp 240..

And a few weeks ago about 30 . 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

[elviukai]

thanks guys. and how I can lower to 0.6v? should I replace r1 with some higher values like 1ohm?

[elviukai]

as I measure all voltages are almost identical in circuit as nelson suggest(+-5%) but 0.66v I can not get 1,1V. if I increase drain voltage of q1 I can reach 0.7v but drain of q1 reaches then 35V(!) what should I do??

[cowanrg]

maybe somehow the resistor was damaged in one of the "blow ups."

test its value outside of the circuit?

[elviukai]

i blew also about 10 0.47ohm resistors 3w. now I am runing 10w resistors..

amp plays 10-20 minutes. is it normal in this circuit that fetw has internal 160C' temperature??in aleph 5 they has only 65..

[Orgonom]

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]

q3 shows 0.62v q d g/d voltage of q5 4.37, q2 4.03, q1- 3.7

[Magura]

Originally posted by elviukai
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??

Originally posted by Magura
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