Pass heatsinks

WayneS

Member
2002-03-24 11:44 pm
Dallas
Unfortunately you're probably not going to have much luck on this path.

You'd have to get your own extrusion tool made. I think it's in the $20k+ range for a die like that. This is a competitive advantage for a company like Pass Labs and they can be expected to guard it jealously.

Finding suitable sinks is the single largest part of making an amp like this. Try R-Theta, Aavid Thermalloy, etc. Even buying sinks from those suppliers will cost on the order of $1000 - $2000 for an amp like that. I had good luck with M&M Metals in Irving, Texas for a pair of Aleph 2's I made, but those amps are "only" in the 300W range. 600W is a TON of heat to reject with no fans, and you can see it in the amp size - it's very big, and a monoblock to boot. THink about it - 2 600W amps is almost a space heater's worth of heat. Good for Canadians.

Let us all know what you finally come up with if you can solve this problem.
 
Wayne thanks,

Actually I'm going to rebuild my Krell KMA-200 Mk2 monoblocks from too noisy fan cooling to quiet convection cooling. Therefore I need big and beautiful heatsinks. There's a Taiwan company, Elite Enterprise Co Ltd, selling amp cabinets similar, if not identical, to the X/XA series. Unfortunately only to volume buyers. Then there's always the option of building your own heatsinks. Anyone had any success in this area?

/Thomas
 
Heatsinks

Hello,
I'm in the process of designing and building my own heatsinks fashioned after AAVID's bonded Fin product.
The heatsink is essentially a 0.5inch thick x 17inch long x 12inch high hunk of aluminum with 49 .090 x .2 inch deep grooves machined along its length. The grooves are there for attachment of the 49 equally spaced aluminum fins which measure 5.5 inches tall by 12 inches long. The fins are then aligned and glued in place with a thermally conductive epoxy. With 600 Watts of dissipation and convection cooled I believe the heatsink rise above ambient is about 40C. Go to the AAvid site at WWW.AAVID.com and check out the heatsink analysis program and information on the bonded fin heatsinks. You can probably find what is needed at the local scrap metal yard.
As soon as I get mine done I'll report on the results.
 
I've built heatsinks before, bonded fin deisgn. But instead of using thermal epoxy with aluminium I used copper and soldered the components together. Solder will have a much lower thermal resistance (unless you're using some strange weirdo mad expensive thermal epoxy). But then again, it wouldn't look to pretty. To make a nice design you'd probably have to machine one out of a solid block of metal, I'm planning on that for my next amp project, was thinking of brass...
 

WayneS

Member
2002-03-24 11:44 pm
Dallas
I saw the bonded fin sinks at Aavid. They came in at about 5x to 10x the price that I finally paid for the extrusions I bought. THey are interesting and work really well if you can afford them. You can also specify just about any size you want as each sink is basically a custom order. I didn't want to have amps that were that expensive though. For some applications they are an excellent answer.

I've seen a page from a fellow that does a similar thing, he takes alternating pieces of 1/8" thick aluminum of different sizes and joins them with long bolts along the length of the "baseplate". I think this a suboptimal way to go though as there are issues with thermal conduction at the boundaries between the pieces of aluminum and also at the transistor attachment points. How do you have a perfectly flat surface to mate to the transistor back plate ? But again, it's a solution that some may find fits their application.

If you're replacing noisy fans, do you mean acoustically noisy or electrically noisy. If acoustic noise is the problem, there are some new very quiet fans you could replace your old ones with. It's another alternative to doing a new case which is many times more work and expense. Just an idea....

As I said in my article on the Pass site, the chassis is the largest part of building a class A amp. It is a place where you will have to do some "real" engineering work - what can you live with on many different aspects given the various and complex constraints you have.

Over and out,
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
I'm working on a feedback scheme for quiet fan operation
using some of the fans out for computers where they
provide a tach output. The idea here is to reliably run
the fan at very slow speeds where it is very quiet.

Even at very slow speeds, the air flow across the sinks
dramatically improves their operation, and the returns
for high speed operation diminish very quickly, so it seems
just about ideal.

I'll let you know what I get.
 
I did some experimenting with some cheap (but very quiet) 80mm Panaflo fans from http://www.mpja.com. I believe the model numbers were f1a or something like that. These 12v fans are rated something like 18dB @ 1m, and can be run down to 6-7v. I can't measure such low SPLs, but I can say that these fans are very, very quiet at low voltage.

They did have a very significant effect on sink temps. In the end my heatsinking was so overkill that I gave up on the idea.
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
For my A75, I was considering mounting the fans inside of an airbox that would sit underneath the amplifier chassis, and which would force air up through the fins. I was hoping to use damping material to isolate much of the fan noise and keep it inside the cabinet. THe air will be filtered with an automotive type air filter- cheap and replaceable.
Where I work, we have a similar system that is used to blow up plastic bags for packing material. It was found that damping the inside of the tunnel where the bags were being filled dramatically decreased the SPL.
If anyone is interested, I will post a sketch or something, although I don't know how well this works until I try it.
Steve
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
Yeah, I've thought of that too- the enclosure should dampen out any blade and electrical noise, but the air noise will be there. I hope to make the enclosure openings big enough that the turbulence will be minimal, and since the heat sink fins are running vertically, I plan to direct the air stream vertically also, so that there isn't the noise of the air blowing across the fins. How effective this is for cooling, I don't know. We'll have to see, I guess!
THanks for the interest.
 
zen fan

thanks nelson for the response.

I am about to try installing a thermostat which may or may not be necessary. I am doing all this in my cold New England basement but hope to be able to used the amp throughout a hot humid summer.
I have found by playing with the spacial configuration of the fan and the sink that i can reduce the rpms/noise alot, its been alot of serendipity and i still have not found the best configuration of the odds and ends sinks and radio shack fans. But i do know that a good fan/sink confguration will allow the box size to shrink, and that passive convection is no help at all, i may as well screw the mosfets to a radiator.

the goal is no "sink" and a slow fan.

I have built a 7" cube from 5/16 plate aluminum. Two side have the mosfets for each channel screwed to them, on one side the xformeris attached, on another side the input/output and power and the remaining sides have fans attached to them. The box is perforated on all sides with 1/8" holes. I roughly calculated the # of holes to allow the surface area to be equal to the surface area of sinks that i found didn't get to hot with a slow moving fan. The goal being to let the box act as the sink when air is drawn across the perforations. I found that positive pressure in the box worked way better than negative pressure. The box may be too small though because the fans have to run to fast and noisy to keep things cool
 
DIY heatsinks

Hi all,

I've been operating my Zen with the chassis displayed on the following web site.

http://home.earthlink.net/~lotusblossom/index.html

This chassis is capable of removing 160 watts of waste energy. I designed it and have been using the chassis' right hand bank for several years with no transistor failure to date. The left hand bank will be used with Nelson's new Zen design.

If you take your time and machine the parts with care the fit will be excellent. If you have the dough and desire the peace of mind, you could go all out and have the bar stock machined to matching tolerance. You could have the parts anodized.... etc. If you require a cooling fan for your larger beast, then use nuts to space the ribs on the threaded rods. The resulting gap will allow the cooling air flow to perform its magic as it passes between each rib.

When using a chop saw, aluminum cuts much like oak. Running it through a table saw is a bit more difficult. Still, I performed the task and have a dandy unit to show for my 16 hours labor.

John Inlow

http://home.earthlink.net/~lotusblossom/index.html
 
Fans seem to all the rage! Has anyone tried to use an electret microphone in a feedback loop to control the speed via the noise output of a fan/heatsink combination? It seems that this approach could be a neat way to minimize the size of the heatsink while keeping the noise under control. Another option could be to also monitor the heatsink temperature and add this to the feedback. The microphones are very inexpensive ($2-3USD) and the rest of the circuitry would only consist of a few opamps, a power- fet to handle the fan current and passive components.
 
Probably didn't have my brain fully engaged this morning. The heat sink temperatue is much better suited for the fan control than the fan noise output since the proximity of the amplifier to the speakers will have a real negative effect on the results if the music sound level prdominates at the microphone position.