Be very careful attaching thermistors to the MOSFETs. I smoked my first F5 build that way. Because of a slight scratch in the coating on the thermistor, a short occurred between the MOSFET drain and the gate drive network that the thermistor belonged to. Poof... In all subsequent builds, I add a small peice of mica between the thermistor and the MOSFET drain lead.
Could you not temporarily disconnect the good channel so that you would be able to use the bulb tester and so not risk frying anything.
If you know you still have one GOOD channel, and suspect you have successfully repaired the bad channel--I'd take some "comparison" resistance checks WITHOUT APPLYING power as your first remediation step. You already have your two most available tools for troubleshooting--a good channel, and a DMM. Check resistances. If you have repaired the board, such comparison checks can give you a good indication of other bad parts, to include resistors, pots, capacitors, semis, and the occasional PCB short or open.
Damage was caused entirely by your unknowledgeable actions.
There's nothing wrong with F5.
DIYers shouldn't be discouraged to build this amp.
Well Katie or Dad, you have learned something that'll stay with you, and a very valuable lesson for others building this amp, or similar projects.
It is disappointing that it cost you a couple of drivers, yes, but now that you've worked out what went wrong and repaired it, there's a tremendous sense of satisfaction and confidence, if you want to see it this 'diy' way.
You just made a mistake (like we all do some times), you figured out the problem (not so easy) and then you fixed it yourself (not so common at all) so, I'd 'take a bow' and pat yourself on the back for a job well done.
It is disappointing that it cost you a couple of drivers, yes, but now that you've worked out what went wrong and repaired it, there's a tremendous sense of satisfaction and confidence, if you want to see it this 'diy' way.
You just made a mistake (like we all do some times), you figured out the problem (not so easy) and then you fixed it yourself (not so common at all) so, I'd 'take a bow' and pat yourself on the back for a job well done.
I completely agree! I was lazy with one of my early F5 builds, so I also had the pots way too high - smoke, but nothing damaged. Turned down the pots and adjusted it properly. Now this amp has been running in my main system without any issues for many years.
I check the bias once in a while, but there is not enough drift to make me want to take off the cover to adjust...
I must have really overcooked mine as obviously some hidden damage was done.
Anyway, it's up and running again.
I put my hands up again, it was my fault. It might have been something as simple as one of the MOS-FETs not being coupled to the heatsink fully, I doubt it as I did monitor each Tj (case) while I was testing it. Initial bias was as something like 3A so something definitely was weakened, the fact that one of the source resistors was found to be OC tells me that one of them eventually fused.
Anyway, it's up and running again.
I put my hands up again, it was my fault. It might have been something as simple as one of the MOS-FETs not being coupled to the heatsink fully, I doubt it as I did monitor each Tj (case) while I was testing it. Initial bias was as something like 3A so something definitely was weakened, the fact that one of the source resistors was found to be OC tells me that one of them eventually fused.
Last edited:
