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toobnoob 17th November 2009 08:32 PM

profile a400xl
got a profile a400xl that needs attention.

have not found much info on it other than a "mosfet" 400 watt bridgeable amp.

i doubt very seriously that this amp will run more than 75 rms per channel into 4, but probably more like 2 ohms.

and it appears to me that the only "mosfet" portion is the fets in the power supply.......

love the marketing.

power supply fets are gone.

"source" resistors not identifiable.

(perry, i will trace the resistors out to see what they go to since i don't have and can't find schematics)

should i bother with this amp?

Perry Babin 17th November 2009 09:06 PM

If no outputs have failed, it probably won't be too difficult to repair.

If you were referring to the gate (not source) resistors, they are likely 100 ohms. I'm assuming that the amp has Z44s in the supply.

toobnoob 17th November 2009 10:06 PM

1 Attachment(s)

the supply fets are 30n06's.

the outputs are tip35 and 36's.

the two resistors that took the brunt of the short circuit unidentifiable.

here is a quick draw of the resistors and where they are connected.

the "??" value is unreadable.

Perry Babin 17th November 2009 10:31 PM

In the only photos I have of a Profile amp, they use 4.7 ohm resistors. Check the 0.22 ohm capacitor to confirm that it's not shorted.

These resistors are not damaged by shorted output transistors. They are typically damaged when the amplifier is driven into hard clipping for long periods of time. They can also be damaged if there is a fault in the amp or the signal line (open shields) that's causing the amp to oscillate at high frequencies.

Perry Babin 17th November 2009 11:05 PM

0.22uF capacitor, not 0.22 ohm capacitor.

toobnoob 17th November 2009 11:17 PM

did not catch that until you posted that....

Perry Babin 17th November 2009 11:23 PM

Neither did I until a friend called and told me about it.

I'm going to learn to proofread one day... just after I learn to spell and type.

lsm_audio 18th November 2009 01:10 PM

hello, usually the resistor in question is about 10 ohms, 1 watt to 2 watts

jol50 18th November 2009 07:09 PM

I had couple of those and bajas. I fix them because they are usually easy to do and appear to be a standard design. IIRC I let the last one go to the local pawnshop in a trade. I tested it, it worked....I'd guess you are right about the ratings but if you needed a 2x ~75 it should work ok, or for a spare or test unit. I've seen worse. They are not worth a lot, maybe I just learn from them lol.

Great number of class AB amps are mosfet PS and BJT outputs. I think they refer to old amps (80s?) that didn't have mosfets in the PS, and they are an upgrade for a PS. Some of the V12 alpines are mosfet outputs, old autotek, I'm sure Perry can list most of them. In the alpines they look pretty puny compared to the BJT they typically used, they can handle a lot of power for their size. I've been told they sound the same, :), I'll be trying a mrv-t757 soon.

I'll look and see if I have another one like that. Have one but don't recall.

BP1Fanatic 5th December 2009 04:12 AM

I have an A400XL that my brother blew in his car. I need to replace the 2.7 ohm 5% resistors (red, violet, gold, gold) at R134 & R234. What wattage is the resistor and where can I get it? Here is a cellphone pic.

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