Thanks for the ideas. I have tried unbalanced and balanced input signals. I get the same results with both.
Yes I did make my measurements with the amp warmed up for over an hour.
DC offsets were both pretty good at around |0.3V| or less.
Last night lying in bed I thought perhaps I have some bad output FETs. A few weeks back I accidentally fried 2 of 4 output FETs. I won’t get into how.
Anyway, I changed the two FETs that were obviously bad, but left two in circuit as they appeared to be working fine. Maybe they are damaged, and aren’t fine after all.
I’ll be removing all of the FETs in order to match them. My test circuit will find any questionable FETs.
Yes I did make my measurements with the amp warmed up for over an hour.
DC offsets were both pretty good at around |0.3V| or less.
Last night lying in bed I thought perhaps I have some bad output FETs. A few weeks back I accidentally fried 2 of 4 output FETs. I won’t get into how.
Anyway, I changed the two FETs that were obviously bad, but left two in circuit as they appeared to be working fine. Maybe they are damaged, and aren’t fine after all.
I’ll be removing all of the FETs in order to match them. My test circuit will find any questionable FETs.
I tested some FETs today and had some very interesting results.
This shows that FETs can seem good but actually be bad!
Here is my test circuit along with graphs for good and bad FETs.
Full Size Pic of Boofers FET Test Circuit and Graphs
I started with my power supply voltage turned all the way down.
As I brought the voltage up, a good FET would never read much above 4V.
A bad FET on the other hand would not properly turn on until the voltage across it reached like 10V.
Then it would suddenly turn on and afterwards behave fine.
I had a few of these bad FETs in my Aleph-X. They all read perfectly fine with a DVM.
They also seemed fine if I set my power supply to 24V and switched it on.
Has anyone seen this behaviour in bad MOSFETs before?
I would really be interested in an explanation as to what is hapenning here.
Is this damage caused from static?
This shows that FETs can seem good but actually be bad!
Here is my test circuit along with graphs for good and bad FETs.
Full Size Pic of Boofers FET Test Circuit and Graphs
I started with my power supply voltage turned all the way down.
As I brought the voltage up, a good FET would never read much above 4V.
A bad FET on the other hand would not properly turn on until the voltage across it reached like 10V.
Then it would suddenly turn on and afterwards behave fine.
I had a few of these bad FETs in my Aleph-X. They all read perfectly fine with a DVM.
They also seemed fine if I set my power supply to 24V and switched it on.
Has anyone seen this behaviour in bad MOSFETs before?
I would really be interested in an explanation as to what is hapenning here.
Is this damage caused from static?
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