Hi
I build 2 F5 turbo V1 channels with low gain (R7-R10 = 100ohm) with a bias of 0.7a per mosfet (irfp240/irfp9240) 32v rails and they have been working nicely for the last 2 weeks until yesterday.
I think the jfets are dead in one channel, R7-R10 gets very hot/smokes. I choose some 7 ma fets.
Can a too high input signal cause this?
The amp gets the signal for a active XO, with some gain max output is +-10v. I was thinking about securing the input using some diodes or should I look for the problem somewhere else?
I build 2 F5 turbo V1 channels with low gain (R7-R10 = 100ohm) with a bias of 0.7a per mosfet (irfp240/irfp9240) 32v rails and they have been working nicely for the last 2 weeks until yesterday.
I think the jfets are dead in one channel, R7-R10 gets very hot/smokes. I choose some 7 ma fets.
Can a too high input signal cause this?
The amp gets the signal for a active XO, with some gain max output is +-10v. I was thinking about securing the input using some diodes or should I look for the problem somewhere else?
The 2SJ108 has a Vgs breakdown voltage of 25V and the 2SK370 40V.
You could try adding 2 x 24V zeners back to back across the inputs as per the Alephs, in fact the Alephs use 9V zeners.
PASS LABS CLONE - ALEPH 4 Amplifier PCB
You could try adding 2 x 24V zeners back to back across the inputs as per the Alephs, in fact the Alephs use 9V zeners.
PASS LABS CLONE - ALEPH 4 Amplifier PCB
I will recheck my XO.
How much voltage swing is to much for the input stage of the F5?
With the "normal" low gain 15.3 db, I will need close to +-6v pk or 4.2v rms to reach clipping with 32v rails.
If that is too much I can increase the gain of the F5 by changing R7-R10 to 200 ohm which should give me about 21 db gain.
How much voltage swing is to much for the input stage of the F5?
With the "normal" low gain 15.3 db, I will need close to +-6v pk or 4.2v rms to reach clipping with 32v rails.
If that is too much I can increase the gain of the F5 by changing R7-R10 to 200 ohm which should give me about 21 db gain.
The 2sJ108 will take 25V as already stated.
That equates to 17V RMS so your 4V RMS is well within limits.
It could be that the inputs have sufferred static damage.
That equates to 17V RMS so your 4V RMS is well within limits.
It could be that the inputs have sufferred static damage.
Have you got long interconnects ?
Or a bad connection ?
Might be worth following my advice in Post #3
Or a bad connection ?
Might be worth following my advice in Post #3
I think I will do it all 🙂
Raise the gain in the F5 and put in some zeners (I think I have some 5-10v somewhere), redo my XO and lower with lower gain.
The interconnects are not that long, but the connection can be questionable.
Raise the gain in the F5 and put in some zeners (I think I have some 5-10v somewhere), redo my XO and lower with lower gain.
The interconnects are not that long, but the connection can be questionable.
What are you using for Xovers if they are the miniDSP modules, I hear they put out quite a thump indicating dc when powered up.
Bill
Bill
if this is the case then consider adding a mute on start up that unmutes after a short delay.
No clue. When I turned the amp off, I head a pop in one speaker. The next time I tried to turn on the amp, it smoked (very hot resistors).
I ran the mosfets at 750 ma each at 32 v rails (350mv drop over 0.5 ohm source resistors).
I have chosen to run with lower bias (600 ma) after measuring how much or rather little power I actually use even when I play loud.
I ran the mosfets at 750 ma each at 32 v rails (350mv drop over 0.5 ohm source resistors).
I have chosen to run with lower bias (600 ma) after measuring how much or rather little power I actually use even when I play loud.
This thread started with you suspecting the input JFets. Have you now discovered that one of the power MOS-FETs has failed ?
The MOS-FETs can fail for a number of reasons.
However, the most likely is a short in the speaker leads, OR, overheating, OR, a foreign object shoprting MOS-FET to heatsink.
The MOS-FETs can fail for a number of reasons.
However, the most likely is a short in the speaker leads, OR, overheating, OR, a foreign object shoprting MOS-FET to heatsink.
I thought it was the input fets, due to the fact that it was the feedback resistors that got hot/smoked (that was after I had turned the bias down to 0).
After some measurements I found that one of the mosfets was conduction at full power all the time no mater what.
After some measurements I found that one of the mosfets was conduction at full power all the time no mater what.
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