[Dreamslacker]

I think you need bigger heatsinks, use thermal compound instead of thermal pads (will explain this later) and use something to apply pressure.


Thermal phase-change pads require high temperatures to become effective. A constant 70'C across the pads for a couple of hours with pressure applied allows them to undergo phase change.
This will allow them to fill in the gaps between the heatsink and the device effectively. Without phase change, they'll not be as effective.
With a long (and tall) bar shaped heatsink you should be able to lay it across the board. On the 2 ends where the PPA logo and the LED output pads are, you should have clearance to drill holes to place screws to mount the heatsink. This will also apply pressure. I don't think you should do this but if you have the confidence and equipment, it will make you feel better knowing that they don't run burning hot.

 

[steinchen]

Quote:

Originally Posted by tangent Would you happen to know that amp's quiescent current?

expected:
opa633 12*20=240mA
ad843 2*15=30mA
opa627 8mA
LED 3mA
classA bias 3*1.5=4.5mA
240 + 30 + 8 + 3 + 4.5 = 285.5 mA

measured: 300 mA

the heatsinks get pretty warm but not burning hot. I'm confident that they'll get their job done (designed for 1GHz GDDR3 RAM). I don't want to drill holes into the pcb to increase heatsink pressure, rather pull the opa633s out and put some Intersil oder Glassman buffers in.

PPA v1.1 done, looking forward to v2.0 & M3

 

[tangent]

Quote:

expected...285.5 mA...measured: 300 mA

I'm not sure I'd worry too much about that difference. It could be attributed to lots of things. Oscillation usually makes for a much more dramatic difference.

Quote:

pull the opa633s out and put some Intersil oder Glassman buffers in.

With the default biasing, the output transistors on the Glassman buffers get quite hot as well. 70C! In fact, my main PPA is sitting on the bench right now waiting for me to get round to slapping some heatsinks on its output transistors.

 

[steinchen]

I don't mind the 15mA, 1mA per opa633 could make the difference. In fact I am surprised that the calculation came that close to the measurement.

I was concerned about the 300mA because the PSU (kit with TL431 from schuro.de) was originally designed for 30V 200mA

Although it delivers the 300mA at adjusted 24V. Nevertheless I will replace it by STEPS, because it induces hum on my PIMETA, though not on PPA (because of rail isolation I guess).

On your STEPS article you recommend the PS1 psu from Welbornelabs.com as an advanced design. As far as I can see the PS1 has no filters etc, what is the advantage of that design ? Are there more specs than low ribble and high noise isolation ?

 

[tangent]

Quote:

you recommend the PS1 psu from Welbornelabs.com as an advanced design.

I meant that relative to the Velleman supply, not relative to the STEPS.

The only substantial advantage I can think of that the PS1 has over the STEPS is that the PS1 is a dual supply. And for the amps on my site, dual is either not needed, or not even helpful.