thermal management

[acebaker]

Grease or tape? Whats your fav. And whats the name of the tape used in amps like the Orion Extreme. And while I'm here. What is the most common cause of crackling noises in amps? It does it when the engines off and it gets worse when it's on (alternator induced) two others in the setup don't make a peep so my power supply is not the source. It's an Orion Extreme 300. The other two are an 800 and a 200. Arguably not Orions best but if you remove those chinsy phase switches and solder in wire they seem to work fine. Tanks,JC

[Perry Babin]

The light blue tape is a silicone rubber filled with ceramic. It's typically called a sil-pad. It's generally very expensive in small quantities.

The Kapton film is also a good insulator. For class D amps and conservatively designed class B and class AB amps, the Kapton tape that's 0.001" thick with a silicone adhesive is good. It's easy to work with and comes in 1" widths (the most commonly used width). For a bit better thermal conductivity, I'd recommend the Kapton 200MT that J&R Electronics sells on eBay (also available from McMaster Carr). He doesn't have any for sale right now but if you email him, he'll list it.

The Kapton would be used with heatsink compound. The sil-pads are not supposed to need compound but I'd recommend also using compound when reusing the sil-pads (they're not intended to be re-used).

The noise may be difficult to find. You need to try to determine if it's being produced in the power supply of the amp or in the audio section of the amp.

[acebaker]

Thanks Perry. I pulled apart an Orion 800 and re-assembled it with the sil-pads and no grease and it's holding up but i'll grease it next time. I'm guessing the grease is still an effective transfer materiel and the tape is more for manufacturing convenience. What's your fave? Kapton and grease or Mica ( i'm assuming that's what is used in the PPI Art's) The 400 has no obvious (visual) issues so the experimenting begins. I'll start with the pwr supply because the noise increases substantially when it gets 14.4 volts instead of 12.5. This amp was used as a sub amp and was likely run at 4 ohms mono and with a small pwr wire. We'll see.

[Perry Babin]

I use a lot of Kapton tape and 200MT (both with compound).

Mica is a good insulator but if there is one insulator per transistor, they're too time consuming to re-use. I replace them with Kapton, in most amps. For amps with larger mica insulators like the PPI amps, I generally re-use the mica insulators unless they're damaged.

Heatsink compound isn't a great thermal conductor but it's better than air. It helps fill microscopic gaps and promotes better thermal conductivity.