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?
 
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!
 
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...
 

Brit01

Member
2008-07-04 10:35 am
ouchhh

25 volts on the speaker. no explosions?? no smoke??

I use the cheapest 1 watt 8 ohm 3 inch speakers for testing.

You don't want any more than 0.5- 1.0 dc on the speaker terminals. magnets do not like DC. I fried 1 test speaker last week with 4 volts (testing an OTL build!). You could feel the hot magnet.
I get concerned when I have more than 15mV DC on my Kipsch speakers from my 380 watt SS amp.
 
I had this rig set up with test speakers for at least 2 hours.

when I went to hook them up to the CHR70's I checked the dc offset and it was ~150mA. I reduced it to ~0 and fired everything back up. That is when the crackle happened.

So please stop lecturing on test speakers...I did that. Sorry to be short but I did the basics and still got burned...

Tinitus...I always wondered if there was a best practice...pre or power on first...
 
Yes,
This is how I hooked up both ends...
f5-2mosfet.png
 

Melon Head

Banned
2006-11-10 10:14 am
Yes, adding current limiting circuitry might help.
But what is the root cause of the problem? There are several others, as well as myself who are using the amp without the current limiting circuitry without problems.
So it seems strange that he is having problems.

He must be heavily voltage clipping the amp.

A picture of the amp might help.
 
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