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Effects of cooling?

Discussion in 'Amps and Cabs [BG]' started by Petebass, Mar 14, 2003.


  1. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Dear everyone,
    I built a floating rack case for my amp recently (pics on the way). The amp vents to the sides, so I incorporated an a couple of 12v, 80mm fans, blowing air into the rack and directly on to the heat sinks on the sides.

    I used it for the first time last night and for some reason, I found myself playing with the volume control considerably lower than normal. I even got asked to turn down a few times. I think it was a case of me adjusting my volume with my eyes rather than my ears, but I've never done a gig with my volume knob in such a low position before and it threw me.

    Was this just a co-incidence? Was it just the room? Or does cooling your amp have this effect?

    PS:- the amp is an "Ebony" (Australian brand), Solid state, 400w at 4 ohms.
     
  2. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    If the amp didn't gradually lose volume from completely cold to normal operating temperature before you installed the fans, it is unlikely that the fans made it louder.

    Pkr2
     
  3. tripwamsley

    tripwamsley

    Jan 31, 2002
    Sulphur La,
    It actually IS likely. Honest. Most of an amplifier's energy is wasted as heat. Speakers are the same way. The cooler your rig runs the more power in reserve you will have. This is physics not magic. I did something similar with an SWR years ago. I had the same results. I digress...Anyhoo....To get back to what I was saying before; If you could design an speaker with 70% power transfer efficiency, you could put it in a lunchbox size cab, power it with batteries and blow the roof off of your house. Really. All this technology with speakers that we drool over, most of the research was done in the 1930's and after. The only thing that has improved is larger voice coils and more power handling. That's all. Petebass, I don't think your nuts!:)
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Thanks guys. PKR2, for the record, I do find myself turning up a bit as the gig progresses, but not a lot. And I'd always put that down to a combination of ear fatigue, slightly warmer voice coils, and a drummer with an extra beer ot 2 inside him. The amp seems to get hot in the first couple of minutes and then temp stabilises, staying pretty much the same for the rest of the set. It didn't actually get that hot, but I thought I'd wack some fans in while I had the opportunity.

    Trip, I'll try it again at this weekend's gigs and see what happens. The Friday gig is a notoriously bad sounding room at which I usually have to play extremely loud to be heard, so it should be a good test.

    PS:- Trip, I definitely am nuts. Ask anyone who knows me :)
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    It's official. With a few more gigs under it's belt, the facts are more evident. I wasn't imagining things and it wasn't the room.

    I'm going to make another rack for my other amp (I've got 2 identical amps).
     
  6. Guitar-player-itis.

    1) Your hearing is de-sensitizing during the gig
    2) Your guitarist' hearing is de-sensitizing (more likely) and you are turning up, trying to keep up.

    Every guitar player I've been with has this disease. It comes from playing without ear plugs.
     
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Pete,

    Unless your amp before was triggering some sort of protection circuit that reduces gain when it heats up, your amp won't be louder or more powerful from being cooler.

    Loudspeakers will become less sensitive when they heat up, but I don't think you did anything to improve their cooling. ;)
     
  8. Is this true? I mean, the amp produces the same amount of heat....without a fan the heat stays around the amp; whereas WITH a fan the heat is blown away....but the amp itself will produce the same amount of heat, that is: will be as inefficient as before. Or am I wrong?
     
  9. tripwamsley

    tripwamsley

    Jan 31, 2002
    Sulphur La,
    Well the only way you can really find out is to try it. The cooler ANYTHING runs the more efficient it will be. I think anyway.
     
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    No, you've got it right, although running cooler makes it safer to run at higher power because it removes the heat from the components that can be damaged by it.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Dang. I trust my ears but now you've got me doubting myself.

    Guess I'll have to make the experiment more scientific. I've got 2 identical amps, one with fans, one without. I might bring them both to a gig, and switch from one to the other mid way through a set. I'll start with the uncooled amp and give it plenty of time to heat up. The I'll switch to the cooled amp with identical settings. I should then be able campare the output of the 2 amps.

    If you have any suggestions to fune tune this experiment, you've got till Thursday night to pass them on.
     
  12. White_Knight

    White_Knight

    Mar 19, 2000
    USA
    Use a multimeter to check the wattage coming out of the outputs perhaps?
     
  13. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I conducted the experiment described above and it seems the fans weren't responsible for any extra volume.

    However on switching from the uncooled amp to the cooled one, the first note I hit drew "why did you turn the bass up?" stares from every member of the band. It seems the percieved loudness I was talking about was in fact 2 diferent sounding amps. Every knob and slider on the amps were identical, but the one in the rack had a distinct boost between 75 and 125hz. A quick twiddle of the EQ confirmed it.

    I decided to run them but at the same temprature so I ran them both uncooled. One amp definitely has a boost at 75hz-125.

    Question - how is this possible given that they are identical amps?

    I don't know if this has anything to do with it, but the one with less bottoms was dropped once (which is why I went and built a floating rack case). It fell from knee height and hit a wooden floor. Could this have something to do with it?

    Both amps are still under warranty so I'm wondering if I should take them to get looked at? Your thoughts?
     
  14. :D

    Hmm...I notice the new Behringer power amp looks a bit familiar...;)
     
  15. Pete, it's been my experience that you should rewire your fans opposite of what you've got them now. I think you mentioned in the first post that you had the fans blowing directly on the heat sinks. Not a bad idea, but keep in mind you're just blowing the hot air around inside the amp then. It's better if you have the fans "sucking" the hot air out of the amp. Of course, I could be completely wrong about this altogether.
     
  16. and I happen to like Behringer products ;)
     
  17. Fuzzbass

    Fuzzbass P5 with overdrive Supporting Member

    Bingo. Although IME, earplugs help little if any.

    To be fair, my #1 band plays a few restaurants so we're in the habit of starting out vewwy vewwy qwiet, gradually turning up to 8, and finally turning up to 11 at the close of the 1st set (that's when the guitarist does his SRV thang and he needs his *tone*, maaan).
     
  18. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Look at it this way: if you're hot and sweaty and want to cool off, do you stand in front of a fan or in back of it?

    You stand in front, of course. That's because the air flow on the exhaust side or high-pressure side of a fan is directed in pretty much a straight line. The air flow on the low pressure side in intake side, though, is coming in from all directions and therefore is more diffuse, although the total volume of air is equal to the other side.

    This concept seems obvious but not all design engineers are aware of it. Amplifiers whose fans suck air through the heat sinks instead of pushing it sometimes tend to suffer from localized cooling deficiencies. The only way to overcome the diffuse air flow on the low-pressure side is to concentrate it through ducting, but even then the flow can be uneven across the cross-section of the duct.
     
  19. What about having two fans? One for intake, and one for exhaust? Would this be effective, or overdoing it?
     
  20. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    If it's done right, that could be more effective than just an intake fan, and would definitely be better than just an exhaust fan. The best thing would be to double them up on the intake side, though.