Replacing mosfets with different/higher spec fets?

ThyDntWntMusic · 28th July 2011, 01:27 AM

is there any issue with doing this?

the amplifier I have is a crossfire BMF1000D.

the mosfets in the powersupply all have holes in them.

not sure if they're the original fets, but they're IRF3205

http://www.irf.com/product-info/data...ta/irf3205.pdf

the amplifier appears to have been repaired before, so these may not be the original fets.

the question is, can I simply replace them with IRF1405's, in the hope that the amplifier will be less likely to fail, due to the higher current handling?

http://www.redrok.com/MOSFET_IRF1405...4.0_TO-220.pdf

Perry Babin · 28th July 2011, 03:11 AM

Unless the user is abusive, the 3205s will work perfectly fine in that amp. There's no reason to use anything else. As far as I know, the 3205s were the OEM part.

Using higher current FETs generally means that they will be more difficult to drive which could mean that the drive circuit would have to be modified for them to work 'properly'. If the amp has a regulated power supply, it may not be immediately obvious that there is a problem with the drive circuit.

ThyDntWntMusic · 28th July 2011, 03:18 AM

well its died twice already.

quite possibly due to low voltage, but I'm not sure as I wasn't the one using it at the time.

anyway, I ordered the IRF1405's, I'll see how it goes/blows.

1moreamp · 28th July 2011, 03:34 AM

Quote:

Originally Posted by ThyDntWntMusic

well its died twice already.

quite possibly due to low voltage, but I'm not sure as I wasn't the one using it at the time.

anyway, I ordered the IRF1405's, I'll see how it goes/blows.

You could have a lot of troubles causing this like intermittently shorted power transformer, Shorted output filters...etc...All of these problems may not be evident on a test bench until you push the amp to full power. Perry's is also 100% dead on about the possible issues you may create when boosting current capacity in a power supply...

ThyDntWntMusic · 14th October 2011, 10:05 PM

still haven't fixed this amp, my stupid desoldering station AND the one I borrowed from work, were both completely and utterly useless.

So, I took it into work last night, and desoldered the old parts there.
Of course, my soldering iron died a month or so ago too, so I might be fixing the entire amp at work

I plan to run this at 0.666 ohm

shall see how it goes, only need it for "burps" so with impedance rise, it should be fine!

JLH · 14th October 2011, 11:01 PM

As far as I know, that amp is not rated to drive that low an impedance. If you keep destroying the power supply, then I would recommend a higher impedance load for the amp. It doesn't make sense to me to keep blowing up an amplifier.

ThyDntWntMusic · 15th October 2011, 08:02 AM

Quote:

Originally Posted by JLH

As far as I know, that amp is not rated to drive that low an impedance. If you keep destroying the power supply, then I would recommend a higher impedance load for the amp. It doesn't make sense to me to keep blowing up an amplifier.

impedance rise.

ThyDntWntMusic · 15th October 2011, 08:13 PM

I run all my amps at half their rated impedance, daily, or quarter their rated impedance for burps, if they'll let me and not go into protect

I've never killed an amp, this crossfire was bought already cooked.

28th July 2011, 01:27 AM	#1
ThyDntWntMusic diyAudio Member Join Date: Feb 2008	Replacing mosfets with different/higher spec fets? is there any issue with doing this? the amplifier I have is a crossfire BMF1000D. the mosfets in the powersupply all have holes in them. not sure if they're the original fets, but they're IRF3205 http://www.irf.com/product-info/data...ta/irf3205.pdf the amplifier appears to have been repaired before, so these may not be the original fets. the question is, can I simply replace them with IRF1405's, in the hope that the amplifier will be less likely to fail, due to the higher current handling? http://www.redrok.com/MOSFET_IRF1405...4.0_TO-220.pdf

28th July 2011, 03:11 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Unless the user is abusive, the 3205s will work perfectly fine in that amp. There's no reason to use anything else. As far as I know, the 3205s were the OEM part. Using higher current FETs generally means that they will be more difficult to drive which could mean that the drive circuit would have to be modified for them to work 'properly'. If the amp has a regulated power supply, it may not be immediately obvious that there is a problem with the drive circuit. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

14th October 2011, 11:01 PM	#6
JLH diyAudio Member Join Date: Apr 2005 Location: Indianapolis, IN	As far as I know, that amp is not rated to drive that low an impedance. If you keep destroying the power supply, then I would recommend a higher impedance load for the amp. It doesn't make sense to me to keep blowing up an amplifier. __________________ Ah, how beautifully the orchestra sounds before a rain! In a dry sunny day there is no way for the instruments to sound this way!

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28th July 2011, 03:18 AM	#3
ThyDntWntMusic diyAudio Member Join Date: Feb 2008	well its died twice already. quite possibly due to low voltage, but I'm not sure as I wasn't the one using it at the time. anyway, I ordered the IRF1405's, I'll see how it goes/blows.

14th October 2011, 10:05 PM	#5
ThyDntWntMusic diyAudio Member Join Date: Feb 2008	still haven't fixed this amp, my stupid desoldering station AND the one I borrowed from work, were both completely and utterly useless. So, I took it into work last night, and desoldered the old parts there. Of course, my soldering iron died a month or so ago too, so I might be fixing the entire amp at work I plan to run this at 0.666 ohm shall see how it goes, only need it for "burps" so with impedance rise, it should be fine!

15th October 2011, 08:13 PM	#8
ThyDntWntMusic diyAudio Member Join Date: Feb 2008	I run all my amps at half their rated impedance, daily, or quarter their rated impedance for burps, if they'll let me and not go into protect I've never killed an amp, this crossfire was bought already cooked.

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