Visonik v2908 power fet substitute

Shane73

Member
2016-02-18 1:57 am
I bought a Visonik v2908 amp for 20. The right channel has blown power fets and blown output transistors. Can I substitute stp50n06 for the irfz44n in the power supply. I plan on replacing all the power fets, at least on the right channel. If stp50n06 is a suitable replacement for irfz44n, should I also replace the left channel power fets? Would I notice any difference between the 2 channels if I don't? Thanks
 

Shane73

Member
2016-02-18 1:57 am
The STP part is close enough.

There won't be a difference in the output of the two channels.

If the FETs in the other power supply survived, there's no reason to replace them.

Thanks. That is what I thought, but it is a massive amp, 39"s long with 12 power fets per channel. I didn't want to plug just anything in it just to power it up and watch it burst in to flames.
 

Shane73

Member
2016-02-18 1:57 am
I have checked the gate resistors and they measure out within tolerances. I pulled the outputs out on the bad channel to prevent that beind an issue. Thanks for the advice on the drivers. I do need to check them. I just want to get this amp powered up to check out the rest of it.
 

Shane73

Member
2016-02-18 1:57 am
I finally was able to power this amp up. It jas a very high draw at idle, 50+ amps and the power fets heat up quickly. I didn't run it for long but it does produce sound on both channels and the output section appairs fine but there is a whine from the speakers when hooked up. I am thinking that since I substituted 50n06 for the irfz44ns for the power fets that I may need to replace the gate resistors. It currently has 68 ohm 1/2 watt resistors in place. Any thoughts?
 

Shane73

Member
2016-02-18 1:57 am
Unfortunately I don't have a scope. I am in the process of buying one but only have a general idea of how yo utilize it (altough a friend of mine is going to instruct me on its full usage). There is an op amp chip that seems to be a part of the driver circuit. I had an issue with one in my MA Audio 802sx. The Visonik amp is made by yhe same manufacturer of MA Audio and is set up very similar.
 
Many people have 12v power supplies with no current limiting control. They use large, low value resistors (100w tubular ceramic 2 ohm is most common) that is inserted in series with the B+ line to allow current limiting which can allow the amp to be powered up and tested (all semis clamped tightly to the heatsink). This can allow you to check things like gate drive signals and current through the output transistors with little risk of damage.

I think I'd pull the rectifiers to see if the excessive current draw is eliminated.