Reversing the fans on a Samson amp

Discussion in 'AV Receivers' started by Felix_F, Jun 28, 2004.

  1. Felix_F

    Felix_F Stunt Coordinator

    Joined:
    Apr 22, 2004
    Messages:
    85
    Likes Received:
    0
    OK, here's my dilemma. My sub amp - a Samson S1500 - is fan-cooled. The fans, located in the back of the amplifier, pull air though the amp in conjunction with a semi-perforated faceplate. I'm going to replace the fans with some very quiet Panflo's and I'm thinking about changing the fans' orientation, too. When they suck the air through the amp, inevitably some dust finds its way inside. One option at hand is installing some non-flammable, non-conductive filter material (I tested it, myself) behind the amp's faceplate. Another option is, of course, flipping the fans over and having them blow inside the case instead. That's the option I prefer, as it'll allow me to install some metal mesh filters on the back of the amp, which can be cleaned very, very quickly and will keep the amp clean inside. I used the same filters on my PC's. BTW, no matter how hard I've run the sub, the amp's fans have not kicked into their full speed.

    The amp's cooling is designed around it running at full power under the most extreme conditions for hours on end. Obviously, my needs hardly meet those criteria and I think that I can safely reverse the direction of the fans; even though, the cooling will be a bit less efficient. Can anyone think of a reason as to why I shouldn't do this?

    Edit: I installed the 2 Panaflo fans this afternoon. Along with configuring them both to blow inside the amp, I also installed some wire mesh filters on the amp's backplate. So far, the Panaflo's are significantly quieter than the stock fans. I'll have to wait until the ambient noise level drops later tonight to gauge just how much.

    I took some reading with a temp sensor of the amp in its stock configuration and after the fan mod. The temp sensor was mounted next to the output device closest to the faceplate, as that's where the direct flow of the fans would have the lest effect - ie. the hottest part of the heatsink. I played (please forgive the redundancy) some particularly bass-heavy Reggae Dub for about an hour, during which I took 4 readings and averaged them to the nearest degree. All temp readings were in Celsius and the ambient temperature was 24C during both events.

    To make a long story short, the temp of the heatsink went up by 2C in both channels - a very small difference. The amp's case wasn't any warmer to the touch, staying very cool - almost cold - no matter how much power was demanded from its outputs, nor did the amp kick the fans into their full speed.

    The amp's stock fans are spec'd at 43cfm @ 2900rpm/ 36dBA. The 92mm Panaflo L1A fans are spec'd at 43cfm @ 2100rpm/ 27dBA. Panaflo fans not only have extremely quiet bearings, but their sonic output is fairly low in pitch, making them sound even less obtrusive. So far, I have to say that this exercise has been a success.

    I feel like I should include a word of warning. If you feel the least bit uncomfortable with putting your hands inside an amplifier - don't do it. Better safe than sorry.

    Felix
     
  2. Wayne Ernst

    Wayne Ernst Cinematographer

    Joined:
    Feb 24, 2002
    Messages:
    2,588
    Likes Received:
    0
    Felix,

    I wasn't aware that the Samson amps "sucked" air though the case rather than sucking air from the back and blowing it towards the front (over the heatsinks) and out the front of the case.

    My Nady pulls air in from the back, blows it over the heatsinks and then the warmer air exits the front.

    I did a fan mod where I purchased some quieter fans (not Panaflo fans, though). The new fans quieted the amp down quite a bit. Plus, even though the fans are pushing a smaller volume of air, the amp still stays very cool.

    Your idea of constructing a "filter" sounds like a good one. The easiest method might be to head to a home improvement store and pick up a pack of thin filters designed for installing in the floor vents of your home. These smaller filters could be easily trimmed to fit the correct size.
     
  3. Felix_F

    Felix_F Stunt Coordinator

    Joined:
    Apr 22, 2004
    Messages:
    85
    Likes Received:
    0

    I actually have some HD filter material left over from our AC/heating system. I figured that I better test to see if the stuff was flammable before I consider placing it inside an amplifier. Ultimately, though, I'm not as attracted to that idea as I am to reversing the flow of the fans and using metal mesh filters mounted to the amp's rear, as I'd have to open the amp every time I wanted to clean/replace the filter material behind the faceplate.

    Best,
    Felix
     
  4. Wayne A. Pflughaupt

    Joined:
    Aug 5, 1999
    Messages:
    6,100
    Likes Received:
    33
    Location:
    Katy, TX
    Real Name:
    Wayne
    Felix,

    I can understand why you’d want to get quieter fans, but now sure why you prefer the air to blow in instead of out. Either direction is going to get dust to the interior. Dust accumulating is a problem anytime you have forced air movement. It won’t simply disappear when you change the direction of flow.

    The cooling system was designed to work the way it does, pulling out hot air. Modify it and you have no guarantee that everything inside gets the cooling it needs.

    If cutting down in interior dust build up is your real goal, the filters you talked about is best the way to go.

    I think you’re really making a problem where there is none, however. The amp’s designers knew about the potential for dust. A little dust really doesn’t hurt anything. The worst that can happen is a little heat build up when it gets bad, and the automatic variable-speed fan will take care of that.

    Just take the cover off and blow it out once a year or so if you’re worried about it. Or just wait until you notice the fan running faster.

    Regards,
    Wayne A. Pflughaupt
     
  5. Felix_F

    Felix_F Stunt Coordinator

    Joined:
    Apr 22, 2004
    Messages:
    85
    Likes Received:
    0

    Thank you for taking the time to reply. In the custom PC world, we refer to the two conditions as positive and negative pressure. Negative pressure - ie. fans sucking air through the amp - yields a lot more internal dust than positive pressure, which stands for more air coming into the case than going out - ie. air blown into the amp.

    Felix
     
  6. DavidLW

    DavidLW Stunt Coordinator

    Joined:
    Nov 21, 2003
    Messages:
    161
    Likes Received:
    0
    I may be wrong but I think a fan is more efficient operating under "negative" pressure. When a fan is sucking and the internal pressure drops, it is easier for the fan to move because there's less air pressure on the blades. This causes the fan to spin faster and lead to greater negative pressure (until the blade is spinning at it's max). However, if it's operating under positive pressure, as the pressure builds up inside, the fan blades has to work against the pressure and thus has to work harder to force the air in. This causes the fan to slow down and internal pressure will the reach a max the fan can push. This explains the "less dust" in a positive condition environment, you got less air movement.

    You can see his in a vacuum cleaner. When you completely block the opening (the sucking end) the motor will speed up. This is because there's no air pressure on the sucking side of the fan and thus no load. On the other hand, if you block the exhaust end, the motor will slow down. This is because a positive pressure is building up and the motor must work harder. I know it's hard to envision with air movement but the same principal applies with a water pump moving water against a head pressure.

    Now, this may not matter in small applications like PC fans and amp fans. And this also assumes the there's a difference between the amount of air that leaves the unit vs the amount of air that enters the unit. Which results in a negative or positive condition.
     
  7. anth_c

    anth_c Stunt Coordinator

    Joined:
    Jul 17, 2002
    Messages:
    79
    Likes Received:
    0
    DavidLW,

    When you put your hand over the vacuum, the motor speeds up because the load is increasing: instead of pulling air at atmospheric pressure, it is trying to pull a vacuum. Although no air is flowing the motor is still working hard: don't confuse a negative pressure with no load.
     
  8. DavidLW

    DavidLW Stunt Coordinator

    Joined:
    Nov 21, 2003
    Messages:
    161
    Likes Received:
    0
    Curiousity got the better of me so I went and wired up a shop vac so that I can place a clamp on amp probe on the hot leg. (I did this by splitting apart two wires of a two prong extension cord and using a cheater plug on the vac.)

    Sure enough, just as I knew it would. The amp probe read 6.95 amps with the sucking end unblocked and drops to 4.96 amps when the end was completely blocked. Amperage drop means less load on the motor and thus the motor is not working as hard.

    Now if you want to argue work in terms of the amount of time it takes to move a certain amount of air. Then yes, the motor has to spend more time to move a certain amount of air. This is because there's less air to move. But never the less the motor itself is having an easier time spinning it's blades. The limiting factor is that the fan also has to work against the outside air pressure trying to fill the void on the other side of the blades. So you can say that a vacuum cleaner with it's end blocked is not doing any work at all because it's not moving any air. All it's energy is wasted on keeping the outside air out at it's blades. Remember it takes about 16 lb of suction to create a vacuum and I know that there are vacuum cleaners that can pick up a 16 lb bowling ball at the suction end. And believe it or not, it is easier for the motor to hold up a 16lb bowling ball than it is for it to move air.
     
  9. Felix_F

    Felix_F Stunt Coordinator

    Joined:
    Apr 22, 2004
    Messages:
    85
    Likes Received:
    0
    Very interesting reading, guys.

    As for my fans, the Panaflo's should arrive tomorrow. I figure that there are two ways I could go about this. I could take the objective approach and use one of my temp sensors to measure the amp in its stock form and then compare it to the Panaflo's facing in both directions. Or, I could take the subjective approach and simply install the new fans configured to blow inside the amp. If I notice fans start running at full speed, I could reverse their direction. As a subjectively-driven audiophile, I've decided to do the latter.

    The S1500 seems to be biased very low. Its case never gets above room temp, and the air being sucked from within feels only slightly warm to the touch. Its two very large internal heatsinks are ~4"x~4" and run the entire depth of the amplifier (~14"). To give an idea as to their size, the Samson's heatsinks are at least twice as big as those in a Behringer 2500. So, theoretically, reversing the direction of the fans should make very little difference. We'll see...

    Thanks,
    Felix
     
  10. LanceJ

    LanceJ Producer

    Joined:
    Oct 26, 2002
    Messages:
    3,168
    Likes Received:
    0
    Personally I would not second guess the amp's designers. The layout of the PC boards, internal cabinet braces and especially, the heatsinks themselves, could all have been placed in specific orientations to cause the most effective cooling results. Reversing the air flow could completely screw this up. I've learned from several physics classes that many things in the physical world are not as obvious as they seem.
     
  11. Wayne A. Pflughaupt

    Joined:
    Aug 5, 1999
    Messages:
    6,100
    Likes Received:
    33
    Location:
    Katy, TX
    Real Name:
    Wayne
    No “could have” there at all, they have been designed that way, period!

    Felix, second guess the cooling design of one amp based on that of another at your own risk.

    Regards,
    Wayne A. Pflughaupt
     
  12. Felix_F

    Felix_F Stunt Coordinator

    Joined:
    Apr 22, 2004
    Messages:
    85
    Likes Received:
    0

    Well, of course it's at my own risk :). I guess I'm not afraid to modify the design due to having quite a bit of experience personally testing airflow dynamics and their impact of case/heatsink temperatures. Everything I know about the subject tells me that the effect of fan reversal should have minimal effect of the amp's internal/heatsink temps, given the scope of its use. There's also a good chance that the temps will be lower due to Panaflo fans' cone-like dispersion pattern, which unlike most other fans aims the air directly at its target. I'll post once I have the fans installed and get a new bearing on the situation. Thank you for sharing your thoughts; I appreciate it.

    Best,
    Felix
     
  13. Felix_F

    Felix_F Stunt Coordinator

    Joined:
    Apr 22, 2004
    Messages:
    85
    Likes Received:
    0
    I edited the original post to include my post-install impressions of the mod.

    Felix
     
  14. karl_burns

    karl_burns Stunt Coordinator

    Joined:
    Nov 17, 2004
    Messages:
    112
    Likes Received:
    0
    In case anyone wouldn't mind, I definitely want a quiter fan on my SAMSON F800 amp. It's LOUD.
    Anyway, what are the specs I need to look for in replacing the fan? I'm interested in the Panaflo fan as described above, but do I have other options? Or what model Panaflo do I need?
    Thanks in advacne for the halp.
    Karl Burns
     
  15. Alan M

    Alan M Second Unit

    Joined:
    Jan 3, 2003
    Messages:
    454
    Likes Received:
    0
    Interesting thread.

    I use a crown 402b to power my mains in my HT.The fans blow air from the back through the front.They were 2 standard 80MM pc fans rated at 46db, 2700cfm.Very loud and annoying.

    I replaced them with 2 PC fans rated at 20db's and 2100 cfm.They are very quiet and as an added bonus,have a slight blue glow that shows through the front of the amp.If the temp reaches 87 degrees,the glow changes to orange(this has never happened even after 5 hours of use).The amp remains cool to touch.

    Was a quick and easy mod that was well worth it.
     
  16. ScottCHI

    ScottCHI Screenwriter

    Joined:
    Feb 21, 2004
    Messages:
    1,292
    Likes Received:
    0
    The airflow goes a particular direction for a reason. Don't change it.

    Regarding the PC analogy, when you design the cooling for a PC you want more air coming out of the case than going into it. This is why, if a PC has only one fan, it always pulls air out of the case. If you build a PC with multiple fans that move air both into and out of a case, you always make certain your outflow fans are at least equal in output to your inflow fans if not greater.

    The idea is to move air OUT, not IN.
     
  17. karl_burns

    karl_burns Stunt Coordinator

    Joined:
    Nov 17, 2004
    Messages:
    112
    Likes Received:
    0
    Thanks for the tips! What exactly are the specs I need to verify/shop for when looking for a quieter fan?
    I'd love to have fans that change colors as an alert!
    Thanks!
    Karl
     
  18. Alan M

    Alan M Second Unit

    Joined:
    Jan 3, 2003
    Messages:
    454
    Likes Received:
    0
    I must admit,I wasnt the 1st person to do a mod on the crown amp.Someone on another forum had posted the voltage for the stock crown fans.

    From that point,I removed the stock fans,They had the cpm and Db's printed on them.I then went shopping to match the voltage and size.The cpm's I tried to match as closely as possible while reducing the noise level(db's).

    Most fans at the local comp warehouse have the voltage,cpm's ,size and db's listed on the box.


    Keep in mind,by replacing the fans,you void the warranty of the amp.
     

Share This Page