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Swordfishy/ASPEN FETZILLA power amp

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S

syklab

Member
Joined 2009
AndrewT said:
Syk,
your FetZilla will run too hot because your heatsink is the wrong shape, the wrong size, in the wrong orientation and is far too thin.

Choose a proper heatsink for the duty !
Click to expand...

Hi Andrew,
Currently this is the largest heat sink available from the local store here in HK , it measures 12" x 4.5" x 1.25". I will order a set with case after the golden week holiday, will you kindly help to determine what will be the proper type and size ?

Thanks
 
A

AndrewT

R.I.P.
Joined 2004
assume a Ta and Ts for the dissipation you need.
From there you can determine the required Rth s-a to which you have applied the necessary deltaT de-rating.

But you must ensure that your de-rating takes account of the thickness of the backplate. This is not usually specified by the heatsink manufacturer due to the way they all assume isothermal conditions for the entire backplate area.
 
S

syklab

Member
Joined 2009
Something bad just happened.
R0020472.jpg


R0020476.jpg


Both channels were working fine on the start-up test before I put them in a temporary case except being a little hot. Today I put them both in a case and connect to a power transformer. After I switch-on the power, a not too loud hum and spark came off from both PCB, it looks like R22 and R24 were blown but everything else looks ok, the fuse still ok. I examine the wiring and discovered that ( I am using only one transformer, a 2 x 26VAC 250VA R-Core) the V+ AC input from left channel and the V- AC input were connecting to the same secondary winding. Could this be the cause to the blown resistors ? What to do next?
 
S

syklab

Member
Joined 2009
Can anyone help to explain what went wrong with my Fetzilla? the fuse didn't got blown, only R22 and R24. What could be drawing a large current that will cause this? I check at the PCB and cannot locate if there is any component had shortened. What should I check next time when I power it up after replacing R22 and R24?

Thanks
 
N

ncc

Member
Joined 2006
syklab said:
Can anyone help to explain what went wrong with my Fetzilla? the fuse didn't got blown, only R22 and R24. What could be drawing a large current that will cause this? I check at the PCB and cannot locate if there is any component had shortened. What should I check next time when I power it up after replacing R22 and R24?

Thanks
Click to expand...

Hi skylab,

I got the same problem before. You could read my post at:

http://www.diyaudio.com/forums/aksa/207772-fetzilla-build-documentation-8.html
Post #80 onward and see how I discovered the problem
 
S

syklab

Member
Joined 2009
R

rho

Member
Joined 2003
I'm sorry if this is already made clear somewhere in the previous 101 pages, but I have a simple question about this amp: Is it designed to drive a 4 ohm load? Or can I drive a 4 ohm load when lowering the supply voltage?

Sorry for my laziness, but I didn;t feel like plowing trough 100 pages of replies to find the answer.
 
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