I fried someting on my F5...ugh - diyAudio
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Old 18th September 2010, 06:04 PM   #1
cjkpkg is offline cjkpkg  United States
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Default I fried someting on my F5...ugh

So I had the double MOSFET going good this morning on the F5 and when I cranked the volume up I lost the right channel. I quickly turned the amp off and brought it back to the test bench...

Now, R5,6,7,8 get REALLY hot and there is no current going to the MOSFETS. Am I fearing the worst that I lost the JFETS?

Also, I am getting about 24VDC on the speaker outputs.

What else would be the likely candidate?
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Old 18th September 2010, 06:36 PM   #2
Zen Mod is offline Zen Mod  Serbia
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do you know how to test jfets and mosfets ?

matching procedure is what you need to test them , and that's easiest way for not experienced DIYas .....

look at FW site for articles - then "mosfet testing" article
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Old 19th September 2010, 04:42 PM   #3
cjkpkg is offline cjkpkg  United States
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I verified that the 2sk170 in one channel was bad.

I replaced with a spare and the same thing happened...at lower volumes everything is a-ok...when I cranked it up the 2sk170 blew agian...and passed full DC voltage to the speaker terminal...

Could a bad ZTX550 also be causing this? I will explore later but I cant keep losing these JFETS!
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Old 19th September 2010, 05:18 PM   #4
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Probably not. How is your F5 different from stock?

Is the output DC positive or negative?

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Old 19th September 2010, 05:23 PM   #5
cjkpkg is offline cjkpkg  United States
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I added another pair of mosfets along with the 47 ohm and 0.47 ohm resistors.

I was running at about 525mA on each of the 4 mosfets...

the DC at the speaker terminals is 22.5V positive...

I should mention that this happened both with an aikido pre and the jfet boz pre...
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Old 19th September 2010, 05:24 PM   #6
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What kind of speakers do you play your F5 with? Did you blow your speakers as well?

Wachara C.
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Old 19th September 2010, 06:23 PM   #7
cjkpkg is offline cjkpkg  United States
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CHR-70's in a fonken cabinet...So far they seem to have come out OK...
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Old 19th September 2010, 09:23 PM   #8
cjkpkg is offline cjkpkg  United States
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Well...all went well on the test bench in the basement...brought it back upstairs to the listening room and adjusted the bias/offset after about 2 hours of listening downstairs...

hooked everything up, the F5 is now in the aikido...turned the amp on, then turned the aikdio on...and...crackle crackle crackle...lost both CHR-70's....

This really really sucks...bad day...
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Old 19th September 2010, 09:41 PM   #9
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May sound cheesy, but learn from this. Get some cheap test speakers or dummy loads.

My condolences.
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Old 19th September 2010, 10:15 PM   #10
a.wayne is offline a.wayne  United States
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Isn't that speaker 3 ohms and only 84 db/1/m ............. maybe clipping the amplifier ?
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