damping heatsink fins

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Hi all,

I don't know if this is the right place for this topic so if not please let me know.

I did a little test of the heatsink fins on my McCormak DNA 0.5. I ran my finger along the fins and they rang at a high pitched level. I put folded, 1/8" thick X 1"diameter, EPDM rubber discs and placed them between each of the heatsink fins and the finger test produced significantly less the ringing. I happen to have a bunch of same size Sorbothane discs and replaced the EPDM with those. The finger test ringing is significantly less...I'd say gone even.

I'm think of putting Sorbothane between the faceplate and front of the chassis. Has anyone tried this on any of their components? I wonder if a bunch of discs or strips, fairly close together, would work as well as full coverage with a sheet. Any thoughts on that will be appreciated.

Thanks,
henrylr
 
Seen some old Moto Cross Bikes?
Some featured a purpose designed rubber strip on each side of the cylinder to "damp' the fins. To keep 'ringing' noise down.
Typically these seemed as useless affectations and either fell off or were even removed by owners.
 
You don't want to block air flow. But one could easily squirt little blobs of silicone caulk sealer between each rung.

But I agree it sounds like a solution looking for a problem. Do the speakers really drive sound into the back of the amp hard enough to ring the heatsink vanes? Finger rubbing isn't a part of normal operation.
 
heatsink damping

Thanks for all the replies. I've read so much about people damping so any components and parts, including the frames of drivers, that I thought stopping the ringing was a good thing.

Regarding airflow and heat: the amp only gets slightly warm after hours of listening at fairly loud levels. Each side of a fin is 9.25 sq. inches and the area of contact of the Sorbothane is like a .14 sq. inch half circle in contact area on one side of a fin. I don't think that will block much air flow or make the fins hotter. I've played it with the Sorbothane and it doesn't feel any warmer to the touch. What about Sorbothane between the faceplate and chassis?
 

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a of bead high damping glue or caulk on the free edge of each heatsink fin, bridging them all with a thin piece of sheet stock may not impede air flow much (or at all, could even enhance "chimney effect" convection but would be hard to design, account or additional flow resistance, size the width of the bridging material optimally)
 
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I would want to see results from damping before assuming it really does anything useful for music. Sure, fins ring when you strike them and chunks of elastomer or struts/webs fitted to the fins will damp that but will enough energy at their resonant frequency/harmonics be transferred to the fins from the air to cause audible resonances in the first place?

You could fit a vibration sensor to a fin and look for anomalies in the swept frequency/amplitude plot if seriously paranoid but at the high SPL necessary to excite resonance with music, I would then be more concerned about personal safety than fidelity.
 
This is just a general summation of what I think of many posts on many audio sites.
I DON'T BELIEVE MOST OF THEM but enjoy most of the replies.

I ask questions in the hope of finding people who have tried what I'm asking about. One can usually tell if the response is reasonable or a rant. Some folks believe tubes need dampers and probably just as many don't. Same goes for just about everything else.

It's a hobby and most tweaks are reversible in minuets. So try whatever you like and let YOUR ears be the judge, but most importantly have fun.
 
This is just a general summation of what I think of many posts on many audio sites.
I DON'T BELIEVE MOST OF THEM but enjoy most of the replies.

I ask questions in the hope of finding people who have tried what I'm asking about. One can usually tell if the response is reasonable or a rant. Some folks believe tubes need dampers and probably just as many don't. Same goes for just about everything else.

It's a hobby and most tweaks are reversible in minuets. So try whatever you like and let YOUR ears be the judge, but most importantly have fun.

I've only been playing with this stuff for 45 years so I haven't seen it all yet but I've never had an issue with 'singing heatsinks'. I suppose they could vibrate a during high volume use but compared to the sound from the speakers, the heatsink noise would be so low as to be 'lost in the shuffle'. Outside of you inhibiting the air flow around the fins (if you run loud this IS important) there really isn't any downside and if it makes you feel better well, OK. Somehow I think there must be SOMETHING more significant to spend your efforts on. If the vibrating heatsinks are actually getting into the output signal, something is seriously messed up.

 
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You can test this by running the amp in a dummy load and listening to your fins. Most fins DO indeed 'sing'; they have a resonance frequency where they can be rather loud and I have seen cases where you could actually follow the music just by listening to the heatsink. The vibrations seem to emanate from the power transistors, when they are heavily loaded they cause vibrations that are coupled to the heatsink.
It is one factor that could figure in audible differences between otherwise similar measuring amps.

I have been experimenting with damping strips connected to the top of the fins to avoid messing with the cooling function, but it is much like trying to damp a speaker enclosure; most things you try only change the resonant frequency.

Jan
 
Thanks for all the replies.

In response to stratus46; I wasn't concerned about actually hearing the vibration...my ears aren't that sensitive. I was thinking it could be related to or effect things the heatsinks are connected to and could possibly raise the noise floor or increase distortion.

In response to jan.didden; I was amazed at how much a few small pieces of sorbothane damped the fins. When I run my finger along the edge, right were the sorbothane is, or along the top or bottom edge of the fins, which is about 2 inches above or below the dampers, the damping affect sounds the same...quiet.

In response to Enzo: If its not the transistors what is causing the vibration? Could it be the chassis the heatsinks are mounted on or other components on the PCB mounted to the heatsinks?

Thanks,
henrylr
 
In my scenario of transformer singing, it is bolted to the chassis solidly, so it vibrates the chassis. The relatively flimsy fins of the heat sink are better able to project that as sound than say the chassis walls themselves. Just my thought. Certain there are other possibilities as suggested by others.
 
I was thinking, about your thought, that the transformer may be the cause of heatsink vibration. So, I thought, why not put some sorbothan between the heatsink mounting features and chassis.

I then thought, if it is the transformer, it must be vibrating other components in the amp. This led me to the question...why not put a sheet of sorbothane between the transformer and chassis and maybe even use nylon bolts? Any thoughts on this proposal?
 
Tread Lightly :)
I did that exact Transformer isolation mounting .. once... As it was audibly humming/resonating the chassis.. annoyingly so.
Real mess resulted, the Mechanical hum was gone but it relocated into the Signal... and into my speakers.
Seems the chassis was an integral part of damping/sheilding of the 60hz electrical Humm.
Only real solution was to remote mount the Pesky Transformer Or Replace it with a better one.
Of which I did neither as the goofy amp wasn't worth the Aggro.
 
Thanks for the interesting info Bare. Maybe all the vibrating parts in the amp, which aren't audible in my system, is how energy is dissipated and kept from going to the outputs.

However, as I mentioned, my concerned was the possibility of the vibration raising the noise floor or increasing distortion. Anyone have thoughts, or experiences, with that?

Just thought that, since its so easy to remove or insert the fin dampers, I'm going to do a little test. I'm going put my ear next to the drivers with and without the dampers and listen for any difference. I'll report back next week.
 
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