I thought I’d share my findings on how to make a quiet 2U cooler for AM5 systems that have a server socket orientation (inline with airflow).
Dynatron is basically the only commercial option available, they offer the A24:
and the A47:
coolers with the only difference between them being a faster fan on the A47.
Fan performance as claimed by manufacturer
9RA fan 7700rpm 38.8cfm 0.52inh2o @ 41dba
A25 fan 7000rpm 40.53cfm 0.56inh2o @ 51.2dba
A47 fan 11000rpm 58.31cfm 1.13inh2o @ 59.8dba
The noise to performance ratio of these stock fans is bad so a 9RA fan can be substituted to improve the situation.
The issue that arises with fan replacement is that the Dynatron fan is constructed with an extra thick, non-standard mounting flange that causes a normal 60mm fan to incorrectly mount to the heatsink:
To remedy this a 9RA-specific 3D printed flow spacer can be made to space the fan correctly and cut down on turbulence:
60mm 9RA fan spacer v2.zip (12.6 KB)
After this spacer is installed onto the heatsink, the two bottom flanges on the intake side of the fan need trimmed with a rotary tool to make room for the AM5 mounting screws:
A 4-pin PWM header will need to be soldered or crimped onto the fan as well since it arrives with bare leads from the factory:
The quiet 2U AM5 cooler is now complete:
A24 vs 9RA fan sound test
I don’t have a way to measure static pressure or flow, although my hand tells me that the 9RA might have a slight edge in flow volume, but I can measure the sound level and electrical load of the fans in the same position and orientation.
Noise floor:
Stock A25 fan:
9RA Fan:
On the 12, 11 and 10 volt measurements of the 9RA fan I had to put some weight on top of it to prevent it from moving or knocking itself over, it wasn’t necessarily because it was making more thrust, but that it’s base was less stable on a flat surface than the A24’s was. The 9RA fan will also run at 1.1v lower than the A24 fan will.