Power MOSFET

[Eva]

By what you tell, I assume that the amplifier is class-D, isn't it?

Then, the problem at high volumes may be due to cross-conduction (new MOSFETs turn-off slower and switching periods overlap) or due to spikes caused by a too fast turn-on activating the overcurrent protection prematurely. Either way, checking gate and drain waveforms with oscilloscope may be the best way to find a solution (that may be as simple as changing gate resistors).

[swordfish689]

Sorry about stealing this thread, but i know that they made 2 versions of the 6500d and the newer version with the fb42n20d had a few more resistors on the output stage. Also it was a much more reliable amp.

[TELLNICK]

I have a mb Quart raa 1000 with the same problem. (it was a broken gift lol) It has a bad fairchild SSP45N20B. i went to the fairchild website and found the same info EVA found, it appears the fairchild SSP45N20B is obsolete, and replaced by the fairchild FDP39N20, and FQP34N20 as eva stated in a previous post "the values are not the same"

hence i have 2 questions:

1) has anyone tried with any luck relaceing a ssp45n20b with a FDP39N20 or FQP34N20?

2)if not is the amp worth fixing? (i have not tinkered much with this type of stuff but it looks like fun even if its not worth fixing)

[1moreamp]

Heres a guy on e-bay but WHEW !!!

http://cgi.ebay.com/SSP45N20A-45N20A...QQcmdZViewItem

If you replace them with the IRF Fets the gate capacitance will be altered and the driver might not be able to handle that. I see MTX amps that use them all the time. And I have seen them being replaced By the the IRF fets mentioned, but the gate resistors were also changed to get the amp to work correctly.

Hope this helps abit


good luck try this link next time you need parts:

http://www.findchips.com/

[Perry Babin]

512-SSS45N20B
http://www.mouser.com/index.cfm?handler=home

This is a fully insulated version of the 45n20B it will not replace the 45n20A (like those used in the early MTX class D amps) but for the 45n20B it works (or always has for me). It's a fully insulated part so you should probably remove the insulator that was previously used and use heatsink compound between the transistor and the sink. You need to replace all that are in parallel with the one that failed.

[sachserjuris]

Hello Mr. Clipped]

Please send to me some mosfet free charge for me build my SMPS.

Thank you very much

Sandro Sachser
Av. Maripa 766
Mal. Cdo. Rondon - PR
Brazil
CEP85960-000

[Formas]

Hello guys, I'm having the same problem with some shot FETs on my MTX amp, they are SSP45N20A actually three of them (2 from left channel and 1 from the right channel).
Did anyone come out with a positive research on what replacements to use?
Thanks for any help as i need this amp to be repaird ASAP.

[Perry Babin]

If the rail voltage is less than ±70v, you can probably use the IRF3415.

If you have any other questions about your amp, start a new thread.