Greetings,
I just picked up a F5 amp and played it for hours and was thrilled. After about 4 hours I switched from my EAR 834L LINESTAGE PREAMP to my Heedroom SS preamp and when I turned on the F5 a funny smell started things off and about 15 seconds later the amp started to smoke!!
What did I do wrong......and does anybody have a clue as to what got fried. I was guessing that it was one or more of those huge caps......just a guess.....I purchased this amp completely built. I don't know how to work on stuff (I'm disabled)........so I'll need someone else to fix it, BUT I need to know what I did wrong!!
Any help from the community would be greatly appreciate. The fellow who sold it to me wasn't willing to help mt trouble shoot......so I'm really in the dark........help please !!
Thanks, musicfan49 (newbie)
I just picked up a F5 amp and played it for hours and was thrilled. After about 4 hours I switched from my EAR 834L LINESTAGE PREAMP to my Heedroom SS preamp and when I turned on the F5 a funny smell started things off and about 15 seconds later the amp started to smoke!!
What did I do wrong......and does anybody have a clue as to what got fried. I was guessing that it was one or more of those huge caps......just a guess.....I purchased this amp completely built. I don't know how to work on stuff (I'm disabled)........so I'll need someone else to fix it, BUT I need to know what I did wrong!!
Any help from the community would be greatly appreciate. The fellow who sold it to me wasn't willing to help mt trouble shoot......so I'm really in the dark........help please !!
Thanks, musicfan49 (newbie)
To review
Your F5 worked great for 4 hours with one preamp.
When another preamp was used - your F5 smoked.
As LoudThud as alluded to - the F5 is a DC coupled amplifier.
Which means if your Headroom preamp put out a line signal + DC voltage,
the F5 will try to amplify both the signal + DC.
As I recall, the EAR preamp is a tube pre - so the output would have a DC blocking cap.
It would put out the signal only.
If your Headroom pre does not block DC it could get passed along to the F5
which would pass it along to the speakers.
The F5 has few components and should be very easy for a service tech to fix.
The parts are easy to get and the schematic is on line.
The bad news is that I hope your bass drivers on your speakers didn't get cooked.
Do you have a receiver to test your speakers ?
.
Your F5 worked great for 4 hours with one preamp.
When another preamp was used - your F5 smoked.
As LoudThud as alluded to - the F5 is a DC coupled amplifier.
Which means if your Headroom preamp put out a line signal + DC voltage,
the F5 will try to amplify both the signal + DC.
As I recall, the EAR preamp is a tube pre - so the output would have a DC blocking cap.
It would put out the signal only.
If your Headroom pre does not block DC it could get passed along to the F5
which would pass it along to the speakers.
The F5 has few components and should be very easy for a service tech to fix.
The parts are easy to get and the schematic is on line.
The bad news is that I hope your bass drivers on your speakers didn't get cooked.
Do you have a receiver to test your speakers ?
.
Good news your speakers are safe.
Your 2A3 SET amp will block DC .
The F5 will let DC through.
If you do not have electronics experience - its best to let a service tech fix the F5.
The F5 has only 4 transistors per side - its has to be the simplest amp in the
world to diagnose and fix.
Plus the parts are very common (all this reminds me of a Dodge slant 6).
To speed things up get a print out of the schematic.
Its on Page 12 here
http://www.firstwatt.com/pdf/prod_f5_man.pdf
BTW: Its kind of a complement to Mr. Pass that this amp is in the company of a 2A3 SET amp.
.
it looks pretty decent
in any case - it needs thorough checking by someone who knows his drek
I can't see NTC's besides output mosfets - are they beneath pcb's ?
in any case - it needs thorough checking by someone who knows his drek
I can't see NTC's besides output mosfets - are they beneath pcb's ?
I am assuming that the photos posted were taken at a time before it blew up?
If so, please take some (well-lit, in focus) photos and post them here. You will be flabbergasted by what some guys can see in a photo!!
If so, please take some (well-lit, in focus) photos and post them here. You will be flabbergasted by what some guys can see in a photo!!
The case looks like its worth a small fortune.
Generally speaking the amp is nicely made.
I see R6 is missing - this is a feedback resistor that is in parallel with R8.
Testing a variation of an F5 with a sinewave generator
all full output - those Feedback resistors got bloody hot.
If the maker left F.B. resistors out - the other F.B. resistors could have been cooked.
Generally speaking the amp is nicely made.
I see R6 is missing - this is a feedback resistor that is in parallel with R8.
Testing a variation of an F5 with a sinewave generator
all full output - those Feedback resistors got bloody hot.
If the maker left F.B. resistors out - the other F.B. resistors could have been cooked.
One could install an AC coupled input on the rear of the amp...
But the issue well could be a parasitic oscillation in the second signal source... not DC offset.
but BOTH channels blew out??
that would be very unusual, which means that likely the fault is at the output end of the preamp/source thingie... a scope would tell all...
_-_-bear
Although... it is possible that the SOA of the output devices was exceeded due to the load, and it took 4 hrs to get the mosfets overtemp enough to go into thermal runaway and smoke?
PS. wow, the builder cuts 45 deg bevels in an aluminum block using a table saw!! very brave.
But the issue well could be a parasitic oscillation in the second signal source... not DC offset.
but BOTH channels blew out??
that would be very unusual, which means that likely the fault is at the output end of the preamp/source thingie... a scope would tell all...
_-_-bear
Although... it is possible that the SOA of the output devices was exceeded due to the load, and it took 4 hrs to get the mosfets overtemp enough to go into thermal runaway and smoke?
PS. wow, the builder cuts 45 deg bevels in an aluminum block using a table saw!! very brave.
If you zoom in fully on the second picture, there's a big brown spot on the right MOSFET to the left of the mounting screw. It could just be a camera artifact, or a blown transistor. Does the black plastic housing look brown and bubbly in the flesh?
- Eric
- Eric
Hi!
I know it's a little bit OT, but where can I get those nice small boards for the F5?
I've seen them a few times since my built is finished.
BTT, I think if both channels are blown up, maybe the problem is somewhere in the AC-DC-supply-section?
regards,
matthias
I know it's a little bit OT, but where can I get those nice small boards for the F5?
I've seen them a few times since my built is finished.
BTT, I think if both channels are blown up, maybe the problem is somewhere in the AC-DC-supply-section?
regards,
matthias
In the center photo, whats the wire going across the left mosfet then glued (red glue) to the heat sink?
Also, the power resistors look a bit stressed, again on the left side. This could be the photo quality.
They look like mine right before they crumbled.
Also, the power resistors look a bit stressed, again on the left side. This could be the photo quality.
They look like mine right before they crumbled.
Last edited:
- Status
- Not open for further replies.