Alesis HD24 Electrical Fan Noise?

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Jeremy H

Active member
Joined
Dec 11, 2005
Messages
40
Location
Australia
I've been hookiing up the HD24 to a Tascam M3500 mixer - balanced to unbalanced.

I had some ground loops big time - but by trying different cable configurations and some star grounding, I have managed to overcome them.
However, with gains turned up on the mixer, I still get a hum that seems to be related to the cooling fan in the HD24. When I switch on the HD24 the hum ramps up as the fan gets up to speed. (You know, like an "audible tachometer"). I have moved the audio leads around but it doesn't effect the sound.

If I lift the ground on the HD24 (I know not wise - but just to try it) the noise stops.

Has anyone come across this? Any suggested fixes?

Thanks as always,
Jeremy
 
I am not familar with the HD24, but well versed on the DC type fans with built-in electronic inverters. If it has a DC fan, place a .1uF cap across the terminals. If noise is still present, try a .1uF from each fan voltage input terminal to the chassis ground.

An alternate is to replace a DC fan with an AC line-voltage fan. If by a small chance it has an AC fan making that noise, use a CorCom filter in-line to supply the fan. CorCom case must be grounded.
 
Hi Amperex,

That was just the information I was after - I believe it needs some type of "suppression".

The HD24 is a hard disc recorder and the fan certainly looks as though it comes from PC technology.

I assume it is a DC fan but I haven't had it apart yet.

Out of interest - does anyone make a range of superior fans in this regard - ie electrically (and acoustically) quiet?

thanks again,
Jeremy
 
I always replaced DC fans with AC types sized at 3-1/8" or larger in my applications. One must also be careful of the operating dB level. A few AC fans are whisper quiet, many are very noisy.

Problem is smaller fans are not available in AC. Thus, one can only experiment unless someone comes forth with test data.
 
it is a DC fan, stepper motor style. I'd recommend the Panasonic Panaflo series (LB1A I think is the right one, there is a low and medium CFM version) - it's just an 80mm fan really. they can be found where you buy computer silencing stuff, like Zalman or Vantec etc...

i borrow an HD24 from work for live recording occasionally, and on site it's fine but when I get it home to the studio it's damn loud! I'm usually just doing transfers so i'm not too worried about it(and it's not mine...)
 
Here's the one a lot of folks on the Yahoo HD24 list use:

http://www.pcpowercooling.com/products/viewproduct.php?show=VCBS

I put one in mine right after I got it and am pleased with the results. Much quieter than the stock fan. Some guys have cut away the sheet metal finger guard and replaced it with one of the wire varieties and report a lower noise floor as a result. I haven't done this as mine is plenty quiet enough now.

Cheers,
--
Don
 
I have my HD24XR hooked up and I have absolutely NO hum whatsoever. Even if I turn my console up to max tape input, master fader and max on the montor volume I get hiss but no hum.

I would check out your wiring setup for balanced to unbalanced. Did you follow recommended procedure for this setup? One wire out of place and you could have enough ground loop to cause problems.

One way to test is disconnect all inputs and outputs and start plugin in one at a time. Does the hum ramp up as you connect more and more? If so probably all your wiring is wrong. If it presents itself with one connection check that wiring and compare to the others you did.

Really unless you have a faulty unit teh fan should make no discernible noise in your circuit.

Jim
 
Hi Jeremy,

Papst manufactures a broad range of fans which are very nice and silent (at least acoustically).

Here's a link to their line of axial compact fans:

http://www.papst.de/index/sid/45106AFB-9A8D-48D9-ADFD-B34D63D67C16/nid/2C2CF297-CDB4-4A99-9C22-553CFAB054D4/produkte_liste.asp

I know they even have a 80x80x25mm 9dB 1000rpm 12V fan even though I couldn't find it on their site now.

Hope this helps,
Suza
 
A big "thank you" to everyone that took the time to respond to my post. A lot of good information!

I'll let you know how it goes.

Thanks,
Jeremy
 
OK guys - I pulled the fan out of the Alesis and this is what I found.

It is a 12v DC fan

If I switch on with the fan disconnected - there is no noise.

I tried the cap across the terminals - could not detect any difference.

I tried 2 caps going from each fan wire to chassis ground - could not detect any difference.

I hooked the fan back up to the unit - but did not bolt it to the chassis. With the unit operating and the fan spinning - I moved the fan around inside the case. There is no noise until the fan gets within an inch of the rear chassis. It appears that the fan does not induce the noise when adjacent to the side chassis. (only the rear where it is mounted.?)

The rear is also where the audio cables are plugged in - However if I move the fan right up close to the cables themselves - there is still much less noise than when it is close to the rear chassis panel.

In fact, where the fan is mounted in the rear of the chassis, is the very worst location, for inducing the noise, in the whole box!!

I can also see - as idylldon said - if I cut out the part of the chassis that forms the finger guard for the fan - the noise would be reduced because it effectively removes the chassis from in front of the armature - where the noise is induced.

However, before I cut up the box, relocate the fan or replace the fan with something else - does anyone have any more ideas regarding suppression or shielding?

thanks again,
Jeremy
 
Glue a piece of tin foil over the motor of the fan with a bare wire in-between the motor & foil. While the glue is setting up, apply pressure to the foil so a reasonable wire to foil contract can be made. Of course, if you have copper foil, just solder a wire to it.

Take that wire to chassis ground. If no improvement, try the power supply negative or common bus if the gear is using a + & - type power supply.

The electronic motor in the fan is emitting a nasty electro-magnetic field. At times, shielding the motor can reduce the electronic noise. Or, simply try another fan.
 
the noise you are getting is turbulence from the fan grill being so close to the fan. Get some snippers and cut out the old fan grill and put a new one on, but attach it and the fan using the little rubber nipple thingies instead of screws - this will also prevent the fan from vibrating the chassis.


check out www.silentpcreview.com - great site, these guys have it going on!!
 
Here's the latest;

Tried the foil shielding - could not detect any difference.

I decided to relocate the fan - without cutting the box. ( for easier resale etc)

I found two 90 mm round metal gutter spigots at the hardware shop - I modded them so the fan bolted to one and the other bolted to the chassis where the fan went but on the outside of the box.

I made some half inch foam gaskets to go between the fan and the spigot and the other spigot and the chassis.

I made up a short piece (about 2.5 inches) of 90mm rubber ducting.

I placed the ducting between the fan spigot and the chassis spigot and secured it with stainless steel hose clamps.

I modded the spigot on the chassis to allow the fan wiring to enter the spigot and go through the existing grill holes in the chassis - back to it's connector terminal.

the only mod done to the original unit was to extend the wires coming off the fan and enclose them in heat shrink.

The result is - the fan is relocated to a spot where it doesn't induce electro magnetic noise into the signal path.

The fan is spaced away from the existing grill in the chassis - so it is acoustically quieter (less turbulance)

The fan is mechanically isolated from the the chassis via the short rubber duct - also making it acoustically quieter.

For the record - whilst waving the fan around outside the box - I found that the EM noise was entering the signal chain via the AC cord to the Alesis! (not the audio connections)

In the original configuration, the fan was mounted immediately adjacent to where the AC plugs in through the back panel to the PS board

Perhaps some AC cord or PSU EM shielding may have helped!?

Thanks for your help guys!
Jeremy
 
not that I read all of this thread before replying, but I just unplugged mine, never had a problem. I then never heard the fan again and heat was never a problem.
 
Hi cwatkins,

Yeah - unplugging the fan crossed my mind too.

Would you say that in your situation the unit is working hard? Like swithched on for long periods - with most tracks being used? Racked up with other gear? (Other heat sources?) Is your room temprature- controlled?

The box is very uncluttered - and it really looks to me that the fan is mostly there to pull air through the holes adjacent to the PSU. The airflow actually drags the hot air from the PSU and then across the motherboard and out??

I thought it may operate OK without the fan cooling, but I wondered if the finer points of digital processing (clocking, jitter etc) may be compromised by chips running hotter?
 
If you check out the HD24 group on Yahoo you will get the best advise for fan replacement (although I think someone here also gave you good advise).

Apart from a bit of noise my HD24XR is dead quiet electronically! I still think you may have a grounding issue in your studio setup.

Glad you found a solution.

Jim
 

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