Large Heat Sinks For Class AB

[concorde1]

I need 2 large heat sinks for my stereo Class AB amplifier build. Ideally, width = 350-400 mm, length = 150-200 mm, fin height = 50+ mm.

So far I have only found Conrad Heatsinks' MF35-151.5, which has a C/W of 0.21 (0.25 corrected). I would like a heat sink with less than 0.25 C/W.

Ideally I will use the heat sinks as the sides of the chassis for the build - that is, no side panels, just heat sinks.

All other heat sinks I have found (on stores like Mouser, Digikey, RS NZ) have been too small, or way too expensive (ABL Components 177AB2000B is 155 USD for one in NZ - this is probably more than I'd spent to get 2x MF35-151.5 SHIPPED).

What heat sinks / heat sink companies are out there that could be suitable?

If there are no other options I will probably go for the MF35-151.5.

 

[hochopeper]

I have used the Conrad MF30-151.5 … works really well. I did have a mishap (broke a tap) when tapping some holes in it … but that was 100% due to my own inexperience with metal work and nothing on the product.

A good reference for understanding the thermal design process is this article - https://linearaudio.net/sites/linearaudio.net/files/v3 euvl.pdf.

 

[diyaudnut]

https://heatsinkonline.com/

 

[tomchr]

https://www.heatsinkusa.com

ModuShop will sell the heat sinks for their chassis separately:
https://modushop.biz/site/index.php?route=product/search&search=heat+sink&description=true

This is also useful: http://heatcal.heatscape.com/natural

+1 for Conrad. I don't think I've seen one in person, but they look very nice in pictures.

Tom

 

[concorde1]

Unfortunately for heatsinkonline, the 11.811" wide heat sink option has only 0.787" high fins.

Similarly for heatsinkusa, the 12" wide heat sink option has only 1.3" high fins. The 8" wide serrated heat sink option has 3" high fins which is more like it, but it's only 8" wide (200mm) whereas I want about 350-400 mm so I can use the heat sink as most of the side of the chassis.

If only Conrad made an MF35-151.5 with higher fins, or an MF35-200. Or if heatsinkusa made a 12" wide version of the 8" wide serrated.

heatsinkusa FAQ says that they can sometimes create custom width heat sinks.

Does someone know if Conrad can do custom dimensions? I've sent a few e-mails to them they haven't replied to yet and I don't want to bombard them with another question.

 

[tomchr]

Anything is available at a price. An extrusion die is around $5k...

Last I checked Conrad offered heat sinks at 50 mm increments on the width. You can cut heat sinks on a table saw with a metal cutting blade. Personally I would just design the chassis to fit the heat sink.

Tom

 

[fluid]

+1 for Conrad. I don't think I've seen one in person, but they look very nice in pictures.

They are the best made heatsinks I have had. They come very flat and well machined from the factory. All of the Chinese made heatsinks were like bananas in comparison. The modushop ones are somewhere in between but they are flat enough not to worry about too much.

Some pictures of Conrad Heatsinks I've used in a few builds. The last one using an LM4780 had 400 grit wet and dry used on it and you can see how shiny it is. The first image used the T bar version, the second some off cuts to cool down a UcD400.

 

[restorer-john]

Why not consider an entire case?

Something like this:
https://www.aliexpress.com/item/100...exp_id=3706da59-e540-45cd-8ee5-d46aa738e2d4-7

https://www.aliexpress.com/item/400...xp_id=3706da59-e540-45cd-8ee5-d46aa738e2d4-15

What is the rating for this amplifer and is it being used domestically or in a continuous high power professional capability. Is it a big class A or something?

The last time I needed 0.55 deg/w was for a 200W@8R/300W/4R Class AB and I went with a 0.65 deg/w as it was the best I could find locally.

 

[fluid]

If only Conrad made an MF35-151.5 with higher fins, or an MF35-200. Or if heatsinkusa made a 12" wide version of the 8" wide serrated.

Conrad have the MF20 151.5 which is 200mm wide, you could use two of those per side to get a 400mm heat sink just like modushop do with their 400mm deep dissipante's.

 

[fluid]

What is the rating for this amplifer and is it being used domestically or in a continuous high power professional capability. Is it a big class A or something?

It's for Tom's MOD686 https://neurochrome.com/products/modulus-686

The heatsink requirements are listed, even in my 5U 400mm deep chassis they still get pretty warm.

 

[concorde1]

Last I checked Conrad offered heat sinks at 50 mm increments on the width.

Wow that would be *perfect*, a 400mm version. I just asked Conrad if they will do two of these.

Conrad have the MF20 151.5 which is 200mm wide, you could use two of those per side to get a 400mm heat sink

Sounds like a good alternative plan.

 

[concorde1]

I just found https://fastron.com.au/collections/...products/8304-heatsink?variant=34829895172230
But it's very expensive, 318 AUD for 2, or 338 AUD for 2 (milled), at 200mm length.
It looks perfect but I don't know if it's worth it.

 

[restorer-john]

I just found https://fastron.com.au/collections/...products/8304-heatsink?variant=34829895172230
But it's very expensive, 318 AUD for 2, or 338 AUD for 2 (milled), at 200mm length.
It looks perfect but I don't know if it's worth it.

I can't believe how expensive heatsinks have become.

 

[fluid]

By the time you have added on the cost of the rest of the panels and supports, anodizing etc. I'm not sure how it comes out much cheaper than buying a modushop chassis. For the larger chassis they are quite price competitive with the Chinese when you include shipping.

About 600NZD for a 5U 300mm Dissipante delivered.

 

[SIY]

Slow moving (and thus quiet) fan. It will make a huge difference.

 

[syn08]

Similarly for heatsinkusa, the 12" wide heat sink option has only 1.3" high fins. The 8" wide serrated heat sink option has 3" high fins which is more like it, but it's only 8" wide (200mm) whereas I want about 350-400 mm so I can use the heat sink as most of the side of the chassis

I tried to use the heatsinkusa stuff for 10 years now; while thermally they are very good, and they will precisely cut it to a custom size, all the big heat sinks had an ugly hidden problem: they are not flat. They come up warped, up to 1/8 inch, which creates a mechanical nightmare if you want to integrate them in an enclosure, as sides. Everything will have to follow the warped geometry. And it’s not an accidental warp, they all and always come so, more or less, it’s totally random.

I ended up with most of the stuff I purchased, and paid shipping through my bleeding nose, used as heat sinks for all kind of dummy loads. There used to be a great company here in Toronto, named R-Theta Thermal Solutions, excellent products at affordable prices; some years ago they got acquired by a big corporation (Mersen, I think) and they no longer sell small quantities, but only B2B. Same story with power transformers, Plitron (now re-baptized as Noratel) no longer sells retail, but with a 5pcs. MOQ. DIY of any kind must die.

 

[concorde1]

Slow moving (and thus quiet) fan. It will make a huge difference.

It's hard for me to picture having fans on the outside of my amp chassis. I feel like it would look really makeshift and be awkward to move the amp round. Not sure if I could get it to work.

I'd be delighted if I can be convinced otherwise though, because the idea of fans sounds good.

Conrad said the MF35-151.5 is as big as they can do. I think I'll just go for the Conrad's, since the Fastron one is too expensive.

 

[fluid]

There are specific heatsinks designed to be fan cooled, plenty of different options like these

https://au.rs-online.com/web/p/heatsinks/6920650

Another possibility from RS, the deeper fins seem to make the rating very good much like the Fastron ones

https://au.rs-online.com/web/p/heatsinks/9033100

 

[Sal1950]

Why not consider an entire case?

Something like this:

I thought I found a super deal for a future built, Till I saw the shipping to US cost.

 

[tomchr]

Slow moving (and thus quiet) fan. It will make a huge difference.

Or one of the super quiet Noctura fans.

Tom