F5 power amplifier

[sangram]

Aww, gee, thanks. I abandoned the test as the thermal transfer was terrible, I'll try the real amps to check it out - once I get my head down and build it up. I now have pretty much everything I need to build it except the solid teak logs for the chassis...

[AndrewT]

Originally Posted by Lucas_G

I wonder how close the thermistors should be placed to the power mosfets.

try gluing the thermistor to the drain lead right next to where it exits the package.

[scranton]

Hi

GOt the F5 working very nicely about a week ago with the generous help of members. The day before yesterday I was hearing a very slight buzz from one of the chassis. Last night it was a bit louder and I thought was coming from the transformer. I tightened down the screw and this morning after 1/2 hour warmup and then listening for 1/2 hour, I noticed it again. Is this oscillation? I don't have any filtering on the inputs. I can install that tonight. Is this coming from the transformer? Thanks

Jan

[tinitus]

I had the same problem recently, and I just loosened the mounting screw, and problem solved
Point is that even a very small and inaudible buzzing can set the whole box in vibration
And THAT can be very audible
Might not be good fore the electronics either

You could try and mount some soft rubbers underneath the trafo, and between trafo and mounting plate, and tighten it loosely
Actually I try to avoid using the metal mounting plate, and use brass screw, but thats a different story

Anyway, as far as I understand F5 may be sensitive to interconnects

[restorer-john]

Sounds like lamination buzzing as the windings heat up. Not much you can do. The better transformers are dumped in a pressure lacquer tank for a few days before being covered and sold.

[sekess]

If that's what it is, I thought it could be fixed by potting. I've never done one myself. But, I think I read somewhere around here that it can be DIY.
However, I don't know specifically what potting material to use or where to get it.

Steve

[labjr]

Originally Posted by scranton

Hi

GOt the F5 working very nicely about a week ago with the generous help of members. The day before yesterday I was hearing a very slight buzz from one of the chassis. Last night it was a bit louder and I thought was coming from the transformer. I tightened down the screw and this morning after 1/2 hour warmup and then listening for 1/2 hour, I noticed it again. Is this oscillation? I don't have any filtering on the inputs. I can install that tonight. Is this coming from the transformer? Thanks

Jan

Which transformer are you using?

[jleaman]

I think i might jump in on this bandwaggon Might order 2 f5 boards from P-Daniel,

Quesitons tho.


Psu voltage per rail ? I think im running 18V on my mini a's will this work ?
will be good with Mini a's?
Going to use with ribbon tweeter.

[restorer-john]

Not too sure about the 'potting' of a Txformer after the fact. You need to uncover the winding cover sheets and somehow find the right potting compound. I have no idea what that stuff actually is, but it'd need to be something that can't attack the enamelling over a long period and also not become porous or affect the dielectric poroperties of the enamel.
I'm sure a transformer winding outfit could help you.

[Melon Head]

Originally Posted by sekess

If that's what it is, I thought it could be fixed by potting. I've never done one myself. But, I think I read somewhere around here that it can be DIY.
However, I don't know specifically what potting material to use or where to get it.

Steve

Two Pack Epoxy