Amplifier case mod

[MarkZ]

Some of you may recall that my equipment is installed in a rack in the trunk, pictured here. (http://www.diymobileaudio.com/forum/showthread.php?t=2509) Therefore, my goal is eventually to have all the amplification installed in the rack. Currently, for a temporary solution, I have my a/d/s/ P840 installed on a rackmount tray to power my front stage. [I've cheated a little by temporarily installing an ESX Q1752 elsewhere to power my midbass drivers.] The sub amp will be installed in the rack this weekend.

I picked up a Directed 600d (600w @ 1ohm) -- the PCB alone. I bought a rackmount case from parts express and some aluminum heatsink off ebay. Attached are pictures of the amplifier alone and pictures of the case with the heatsinks and mounting spacers installed. Next on the list is the three (quiet) fan setup, the connections plate on the back (XLR input, binding posts for everything else), a relay circuit to power the fans, and tapping the heatsink to mount the transistors to them. Hopefully it'll all be done tomorrow.

[bobditts]

hey mark, question for you. is there anything special you need to do to get that rack mount eq to work with the 12V audio?

[MarkZ]

No, I just use a power inverter for the DCX. Some people do use a 12v mod though.

[bobditts]

how large of an inverter do you need for something like that? do the rcas need to be modified at all?

[MarkZ]

I assume you still mean the Behringer DCX unit. It's low power, so a small inverter is fine. I think mine's like 120w or something to power three units.

And you need to buy/make XLR->RCA cables.

[MarkZ]

Day two.

Installed back panel with binding posts for power/gnd/rem (right) and speakers (left). XLR input connector not visible in the dim picture. Also, three fans were installed - one next to power binding posts, and one blowing across each of the two heatsinks.

Second, I put together a relay circuit (second attachment). This accepts the remote input and provides outputs for the remote input of the amp and the three fans. In addition to the relay is one fuse holder, one quenching diode, and one series diode/parallel capacitor to drop and smooth the voltage going to the fans.

[chad]

Did you bare the metal down between the chasis and heatsink? Sometime I have found that to help in heat transfer, use lots of white Acky-Pucky heatsink compound! Don't get it on your clothes, unless you find it a fashon statement!

How do you plan to do heat directing? It will work best if there is a (one) positive direction of heat flow, make the outlet larger than the inlet as to allow the flow to expand. Many proven professional designs actually have "Ducting" in place, especially for the heated air, you want the heated air to escape as efficiently as posible and get the hell away from the amp :)

Chad

[MarkZ]

Did you bare the metal down between the chasis and heatsink? Sometime I have found that to help in heat transfer, use lots of white Acky-Pucky heatsink compound! Don't get it on your clothes, unless you find it a fashon statement!

I considered it, but the bottom of the case is not flat. The heatsink is already sitting on a slight ridge. I suspect that adding heatsink grease wouldn't be enough to enhance the coupling appreciably.

How do you plan to do heat directing? It will work best if there is a (one) positive direction of heat flow, make the outlet larger than the inlet as to allow the flow to expand. Many proven professional designs actually have "Ducting" in place, especially for the heated air, you want the heated air to escape as efficiently as posible and get the hell away from the amp :)

There are two fans that blow across the heatsinks (towards the right) and a third fan on the other end that blows out of the case. The heatsinks themselves act as the ducts, nearly extending all the way to the "ceiling". I've been considering "ducting" the fan on the front heatsink (top of the picture), as it's not very close to the heatsink due to the board placement.

[shinjohn]

Awesome job Mark. Nice work. It's always great to see creative stuff like this!

I considered it, but the bottom of the case is not flat. The heatsink is already sitting on a slight ridge. I suspect that adding heatsink grease wouldn't be enough to enhance the coupling appreciably.

There are two fans that blow across the heatsinks (towards the right) and a third fan on the other end that blows out of the case. The heatsinks themselves act as the ducts, nearly extending all the way to the "ceiling". I've been considering "ducting" the fan on the front heatsink (top of the picture), as it's not very close to the heatsink due to the board placement.

A couple of notes/comments: all TIMs (thermal interface materials) are not created equal. The higher end materials used for CPU/processor interface have significantly higher performance than "standard" thermal greases. Get some Arctic Silver from a computer components house if you can. It is readily available and works great. The other important factor is surface roughness to assure the best contact between your heat sources and the sink. If the bare heat sink extrusions are not very flat, I would probably machine the contact surface prior to afixing the transistor cases to them.

I would also recommend you use a duct of some kind to direct the air flow of the fans through the heatsinks. (In other words, duct from the fan to the HS, and also shroud the top of the HS fins along the entire length) It will increase the efficiency of your setup. Also, if you can space the fan that is pictured in the foreground more like the fan that is farther away, that is probably better. Fans will perform optimally with some plenum to help develop the air flow. The fan in the foreground seems just a little too close to the heatsink for comfort.

One other note is that the orientation of your heatsinks is not optimal, if I understand your design correctly. I am assuming you are interfacing the transistors to basically the inner most fins of the heatsinks. What this means is that the majority of the heatsink won't be effective in cooling. The single fin will get really hot, and then the transfer of the heat to the other fins will be bottlenecked as a result. If you could orient it such that the base plates of the heatsinks faced inside, and thus were interfaced to the transistors, your spreading resistance decreases, and all fins will be more effective at transfering the heat load. This is not to say that your current design won't work, but just a consideration. Please don't take this as any kind of criticism, just some observations I had looking at it..... :p

Anyhow, just a couple of comments that might help, based on some of my work/industry experience in thermal design/cooling. Hope it helps! Good Luck and keep us posted! :D

[MarkZ]

A couple of notes/comments: all TIMs (thermal interface materials) are not created equal. The higher end materials used for CPU/processor interface have significantly higher performance than "standard" thermal greases. Get some Arctic Silver from a computer components house if you can. It is readily available and works great. The other important factor is surface roughness to assure the best contact between your heat sources and the sink. If the bare heat sink extrusions are not very flat, I would probably machine the contact surface prior to afixing the transistor cases to them.

I'm using silpads to affix the transistors to the heatsinks. They serve to electrically isolate the transistor (rail voltage) from heatsink (ground), and not as messy.

But yeah, I'll probably put some between the heatsink and case as Chad suggested.

I would also recommend you use a duct of some kind to direct the air flow of the fans through the heatsinks.

I've been thinking about this since Chad brought it up. The difficult part is to form a sizable duct that avoids the circuit boards. I can't wall off the right side because the electrical connections are there. The left side is air inflow, so there wouldn't be much point of doing that. Additionally, the circuit board I made has to be mounted on the right side as well, making it difficult to run a duct from the front of the case to the "output". Once everything's in there, there isn't much real estate to work with. So barring an elaborate duct setup, I'll probably just rely on the fans as is.

It will increase the efficiency of your setup. Also, if you can space the fan that is pictured in the foreground more like the fan that is farther away, that is probably better. Fans will perform optimally with some plenum to help develop the air flow. The fan in the foreground seems just a little too close to the heatsink for comfort.

Maybe I'll try to move it back a little then. It can only go back maybe an inch though before it begins to interfere with the binding posts. But an inch could be a big deal.

Thanks for the input!

[shinjohn]

I'm using silpads to affix the transistors to the heatsinks. They serve to electrically isolate the transistor (rail voltage) from heatsink (ground), and not as messy.

But yeah, I'll probably put some between the heatsink and case as Chad suggested.



I've been thinking about this since Chad brought it up. The difficult part is to form a sizable duct that avoids the circuit boards. I can't wall off the right side because the electrical connections are there. The left side is air inflow, so there wouldn't be much point of doing that. Additionally, the circuit board I made has to be mounted on the right side as well, making it difficult to run a duct from the front of the case to the "output". Once everything's in there, there isn't much real estate to work with. So barring an elaborate duct setup, I'll probably just rely on the fans as is.



Maybe I'll try to move it back a little then. It can only go back maybe an inch though before it begins to interfere with the binding posts. But an inch could be a big deal.

Thanks for the input!

Looks like I was editing while you were typing! :D :p

Take a look again as I added some more comments. In any event, GOOD LUCK! :D :D

[MarkZ]

Looks like I was editing while you were typing! :D :p

Take a look again as I added some more comments. In any event, GOOD LUCK! :D :D

Yeah, that was sort of an unavoidable problem with those heatsinks. Getting heatsinks is hard (and expensive). Getting them to perfectly fit inside a 1U case is even harder. Your point is well-taken, but there's nothing I can really do about it now (I tried fitting them "sideways", but no dice).

The other amplifiers I'm working on are my own design, and I'll be using TO-3 cases mounted within holes drilled in the heatsinks, so I'll have no such problems. ;)

[shinjohn]

Getting them to perfectly fit inside a 1U case is even harder.

I know. I've designed a few 1U servers before. :p :D


The other amplifiers I'm working on are my own design, and I'll be using TO-3 cases mounted within holes drilled in the heatsinks, so I'll have no such problems. ;)
Sweet. :cool:

[chad]

The problem with TO3's is that they are going bye-bye. They are getting expensive and being phased out. Prices have tripled in my area fro repair work for factory certified components and imposteurs are madly abound! Beware!

As for ducting, just some pressboard stuff man, we aren't doing HVAC for the pentagon here. I don't know what it is but it's rigid, heatproof and orange in color. About as thick as 3-4 playing cards. Just enough to get the air in and out. If you can get to internal pics of a QSC RMX series amp you will see what I am talking about. this stuff is non conductive and can be set right on the board and bent to shape, again, it does not need to hold water, just direct air.

Chad