One of the first and only negative thing I noticed about my SDR1K on its initial setup this weekend was how much fan noise there was with it sitting on my desk. Since I knew that the fan noise was being picked up by the microphone and I really didn't want to put the unit under the table (can't show it off when it is out of sight), I decided to do a little research to see if there was something I could do to reduce the fan noise and share the process with the group.
My first though was "just get a quieter fan." I first removed the fan from the front panel so I could get the part number and retrieve the data sheet from the web. What I discovered was that the specifications of the fan used by Gerald & crew in the SDR1K are the upper range compared to other 80mm X 15mm fans. No skimping here - Thanks Gerald! As per the data sheet, the fan provides 22 CFM airflow @ 2000 RPMs generating 23 dBA of noise. After an extensive search of the Internet I could not find a fan with better specifications. So, the quick fix was out of the question (isn't it always) It didn't take too much effort to figure out that a large component of the fan noise was the volume differential between the fan intake vent and the volume of air being drawn in by the fan. Just by looking at the air intake holes located within the area of the fan casing, it was fairly evident that approximately 50% of the total area was blocked. A simple test of this theory was to fire up the SDR1K while holding the fan next to the chassis vent holes and moving it away by 10 mm. The fan noise decreased at least 80%. Now I had two options. One was to use small stand offs on the fan mounting screws to decrease the pressure differential or modify the chassis to allow more air through the fan intake opening. Not wanting to disturb the laminar air flow by creating an inefficient open loop, I opted for the later option. The mod: I disconnected the power switch, mic connector and fan and then removed the front panel from the chassis. Using the outside of the existing air holes as a guide, I scribed an octagon on the front panel by creating a tangent across three successive vent holes creating eight sides. Using my trusty Dremel tool (a most excellent toy) and a metal cutting wheel, I cut out the octagon traced on the front panel. You want to make sure you don't do any metal work with the electronics in close proximity since the cutting process creates very fine metal dust that gets everywhere. I smoothed up the rough edges with a grinding wheel and then used a little flat black paint to cover the exposed metal edges. I replaced the front panel back into the chassis along with the mic connector and power switch. When I reinstalled the fan and the bezel, I used some small flat rubber washers in between the fan and front panel to dampen the harmonic vibrations the fan induces when the fan is running. I replaced the snap-on dust filter and fired up the SDR1K. The results were instantaneous and absolutely amazing. I probably reduced the fan noise by 100% easily. The fan in the Astron SS-30M is louder than the SDR1K and it is a relatively quite fan. One added benefit of the modification was the increased volume of air flowing over the PA heat sink increased its thermal dissipation efficiency. Subjectively, I could feel more air flowing out the exhaust holes and the temperature of the exhaust gas was somewhat less than it was before the modification. The whole process took less than 30 minutes to complete (minus the time to go the Lowes to get some rubber washers). I now wish that I had a way to measure airflow and to take some "before and after" temperature readings of the exhaust gas along with some pictures documenting the process so I could provide a more complete assessment of the benefits resulting from the modification. All I know is the SDR1K is much, much quieter, the PA runs cooler and since the fan experiencing less mechanical and thermal stress, it should last longer. I have a large (500 MB) close up jpg of the finished product without the dust filter if anyone would like to see it. Just send me an e-mail directly and I'll forward it on. 73 de W4TME -Tim --- Tim Ellison <mailto:[EMAIL PROTECTED]> Integrated Technical Services <http://www.itsco.com/> Apex, NC USA 919.674.0044 Ext. 25 / 919.674.0045 (FAX) 919.215.6375 - cell >>> PGP public key available at all public KeyServers <<<
