FET insulators

[mnhiphop101]

Amp manufacturers use different thermal insulators on the ps and output sections. Im curious to know why the output sections get the yellow foamy insulators. I'm sure someone on here knows.

 

[Perry Babin]

Are all of the FETs TO-220 case?

 

[mnhiphop101]

No TO-3pn like the 24n40f package on the output and TO-347 like 064n's

 

[Perry Babin]

I've seen the larger case transistors that didn't lay perfectly flat and they appeared to be using the thicker insulator to try to get better thermal transfer than they could with harder, thinner insulators.

It's possible that the thicker insulator is more conductive (thermally) but high performance insulators of that type are typically very expensive.

Maybe someone else has a more definitive answer.

 

[ultra]

In my opinion it has to do with the EMI. Class D output stages are transferring noise to the chassis.
By using thicker insulation EMI is reduced. Some manufacturers use ceramic insulators instead.