F5 Turbo questions - 100W+

[exponent]

I read through the design spec and notes regarding higher wattages. I have read that two limiting factors to consider are the power supply and the heat sink. It is easy enough to beef up the power supply BUT my questions are about the heat sinking required. I would like to have a max power output of 100-150W and will be driving an 8 ohm speaker. How much heat sink is required to handle say 120 Watts. The enclosure I have has 14"deep X 8" high X 2.25" wide heat sinks. There is 1 this size on each side. It's a lot of heat sink. I am thinking of doing a stereo version but need to know if this heat sinking is enough. If not then I need to go monoblocks. The cases are expensive so if I can get away with one that would be best.
1) IS the described heat sinking enough?
2) I am going to use a thermostat - what temperature should I use for cutoff?
3) I'll probably go with an external DC supply - any guidance on how much I need for filter caps is appreciated?

 

[Nelson Pass]

Sounds like a pretty decent sink. Use it and bias the amp up until the
sink settles in at 50 deg C. and be happy.

Most of my projects use about 60,000 to 120,000 uF per channel.

 

[exponent]

Cool. That makes me very happy. Just one more question - I may have been a bit vague. I am going to use a thermostat for safety reasons and will probably be placing it on a heatsink close to a transistor. At what temperature should I select a thermostat for? The idea would be to cut the power supply rails on critical temp.

 

[Zen Mod]

either at sink or at middle of case , as Papa is doing with FW amps

if on heatsink , near mosfeet - take 65 to 70C

if on mid of case ...... say 5 to 10C less

sorry , forgot which exact value is Papa using

 

[exponent]

Thank you for the response. I am thinking of going with 48V rails and source resistors of 0.47 ohms. This time around I am going to ask more questions before building. I am also going to use IRF9240 and IRF240 FETS in the output. Can you comment on these design choices?

I am leaning towards a separate power supply as I can put it in a fairly cheap enclosure compared to the amp enclosures

 

[Zen Mod]

gimme a pic of your heatsinks

take in account , as reference - Modushop 5U/500(deep) case is good for 120-130W of heat per side

regarding cap bank - isn't there some info in F5T article ?

say that I wouldn't go with less than 4 x 47mF per channel , along with 0R1 for CRC filter ......... 47mF-0R1-47mF per rail

 

[exponent]

I am thinking of somewhere around +/-50VDC for the rails. I am OK with the power supply filtering but just wanted to know what +/- DC rails you have used in your build? Picture of the sinks are attached. Each sink weighs 20 kg.

 

[Zen Mod]

oh yeah ........ you bought smaller PL knock-off from Aliexpress

🙂

you're good for 130W of heat per side ........

 

[exponent]

Thanks for your help. It is appreciated very much.