In a discussion of the heat output generated by the latest Onkyo AVR models, I had mentioned I had built a simple DIY cooling solution for my system. Per request, I've documented the components and structure below.

Parts List per Assembly
4 - 2" 8-32 stainless bolts
8 - #8 stainless washers
8 - #8 32 stainless nuts
4 - rubber cap feet
1 - Scythe S-FLEX SFF21D 120mm Case Fan
1 - 12v DC power supply

Hardware (http://www.orderofgarpike.com/cooler/02_hardware.jpg)

Asssembly is very simple, essentially you are creating "legs" for each case fan to allow it to stand off over the top vents of an audio component.

Fan (http://www.orderofgarpike.com/cooler/01_fan.jpg)

The Scythe S-FLEX SFF21D is an utterly silent fan even at full RPM. It's rated as 8.7dbA, but it's likely a bit louder than that. In any case, the fan is completely inaudible to me at any distance greater than 3 feet in an otherwise quiet room and moves a respectable amount of air.

This is the order that I used for assembly. The washers help to prevent thread over/under tightening. Also it gives a slightly more finished look.

Assembly (http://www.orderofgarpike.com/cooler/03_assembly.jpg)
Assembly (http://www.orderofgarpike.com/cooler/04_assembly.jpg)

Complete profile views of the fan assembly:
Side Profile (http://www.orderofgarpike.com/cooler/05_profile.jpg)
Bottom Profile (http://www.orderofgarpike.com/cooler/06_profile.jpg)

12vDC Power Supply (http://www.orderofgarpike.com/cooler/07_psu.jpg)

The 12v DC power supply I chose was found at a local electronics surplus store for about $6. Don't feel compelled to spend Radio Shack prices unless you absolutely must. If you have noiser fans, you may want to undervolt them with a 9v DC power supply instead. If you have any 9v DC power supplies laying about the house they will also work for this purpose.

I wired my fans in parallel to the power supply. (both fan positives to the DC positive, both fan grounds to the DC ground)

The DC power supply is plugged into the switched accessory AC outlet of the AVR, which allows the fans to only be activated when the unit is online. Nifty.

A couple of shots of the fan assemblies placed on top of my Onkyo TX-SR875.

Placement (http://www.orderofgarpike.com/cooler/08_location.jpg)
Placement (http://www.orderofgarpike.com/cooler/09_location.jpg)

Having two independent units allows me to selectively target the two hotspots on the 875, the amplifier heatsink and the REON chipset.

There has been some discussion as to whether a "push" (air down into the unit) or "pull" (hot air out/up) is better. In testing it seemed the "push" method cooled better, but might contradict the normal cooling mechanics of the unit. As such, I've reconsidered my original position and have configured the fans to "pull" (hot air out/up). This still yields a significant amount of cooling.

Pre-cooler, I was able to read temperatures coming off the REON chip around 150'F with ambient room temperatures of 78'F. Post cooler application, temps are now range between 80'F - 90'F. No more blistered fingers!

Enjoy! Comments are welcome. This design could easily be adapted for other equipment and applications.

Moving our previous posts out of the other thread:


Originally Posted by Tspeer
As far as heat goes, they run hot but I think they all run hot. The higher power output the hotter, as observed by someone who works at circuit posted above. I own an Onkyo 875.

Actual temperature readings, a fact finding investigation brought to you by yours truely.

Test methodology, played The Matrix HD-DVD in TrueHD, at +2 db ( i.e. PRETTY DAMN LOUD(tm) ) all the way to where the helicopter crashes into the glass building, and right as that was happening took a temperature reading with a MicroTemp. The highest temperature I recorded from my TX-SR875 was 150F/66C. The Reon chip does seem to run really hot and is the source of some of the highest readings measured. The unit sits on the top of an open-air stand (StanDesign) and has free unobstructed airflow all around.

As far as comparing temps to other receivers or electronics equipment, my old Onkyo which lasted 9 years ran pretty hot as well, but not quite as hot (it was not as powerful either). I've measured temps from my video card in my pc, an nvidia 9800gx2 and recorded 148F or so temps from it.

Conclusion: Yes, it runs hot, but so do plenty of other receivers and other electrical devices. Who is to say it's too hot? The engineers who designed it knew how hot it would run. These receivers have ran hot all thru-out my 10 year or so exposure to those made by Onkyo. It is nothing new. And it isn't something to be worried about unless your receiver is in an enclosed cabinet, in which case some cooling solutions are available. That would apply no matter the brand if it is a unit of sufficiently high power capacity.

Back to the regularly scheduled ranters


Originally Posted by KingLeerUK
I too was experiencing some crazy heat issue with my Onkyo TX-SR875. I have my unit in a Boltz open-frame rack with 10" open air above it and wide vented slots to the sides. The back of the rack is open. I was measuring temperatures around ~152'F coming from the REON chipset area of the unit. What was somehow darkly amusing was that I don't even have the unit processing video from my Blu-ray player. I directly feed component video to my display (only 1080i capable). Thus, the REON chipset should not have been processing video anyway.

After thinking about this for a few weeks, I came up with a low-cost solution that has ended up working brilliantly.

I bought a pair of Sycthe 120mm cooling fans (PC case fans) from Newegg. These fans were rated at only 12dB when running at full speed. Locally, I purchased a 12v DC power invertor and some 2" mounting bolts, with matched nuts and washers. Finally, I found some rubber cap feet that fit snugly to the bottom of the bolts. I used the bolts/nuts/washers/caps to create "legs" for the fans by running them through the mounting holes. This allowed me to create a 1 1/4" space "under" the fans.

I now have two fan assemblies that I can selectively position over the hotspots on my 875 (the amplifier and the REON chipset). I experimented with both "push" and "pull" configurations and found that the "push" (air blowing into the unit) provided the best cooling. Where once I was risking blisters to touch the top of the unit it now only runs lukewarm to the touch. The real beauty is that the 12v DC supply is plugged into the accessory switched AC output of the receiver and only comes on when the unit is activated. I've been able to detect no audible interference in the audio output (I was originally concerned about introducing hum) and the fans are completely inaudible when energised.

I'll take pictures and write up more thorough instructions if anyone is interested.


Originally Posted by Tspeer
Thanks for the info about pushing the air being more effective. I've ordered 2 of the large versions of this: http://www.coolerguys.com/ccstandk.html It uses enlobal fans, which are super quiet (got 4 of them in my PC). I know they are a bit expensive for just being a metal shelf but it will have a nice sleek look. That thing gurkey has looks pretty good as well. Simple too.

I think what I will do is use the push method, and install air filters on the tops of the 120's. I've got some grill shaped 120mm air filters similiar to these http://www.coolerguys.com/840556041146.html that I'm going to try using. But I also ordered 4 of these since they look sleeker and may fit better: http://www.coolerguys.com/120almmesh.html

A bit pricey when all done but should be nice and contained. The air filters are washable under the sink.

Thanks for posting the steps.

One comment on your DIY steps, wouldn't it work better with shorter legs on the fans? Then perhaps the Pull method (pulling air up thru the component as opposed to pushing it down) would be more effective?

I think I still want to try the push method so that I can filter the air going in. If it is sufficient CFM of airflow, it will not really matter that it's going against natural convection. I would estimate natural convection at a few CFM at the most. So installing filtered fans at 20 or so CFM should move plenty of heat and air out of the unit.

I should get my cooling rack on Monday, I'll let you know how it works out.

One blowing in and one blowing out, perhaps on opposite sides, would probably be ideal. This looks very simple however. How are the results?

Nothing new. I've been doing this for years.
Much simpler to use rubber feet with the stickem stuff on them. 1 in each corner of fan, place fan in center blowing up.
Wall wart plugged into switched outlet of AVR so fan comes on with AVR.

Check out the "Adding a cooling fan to AVR cabinet" thread in the Tweaks and DIY section.

Bob, where did you get your rubber feet for the fan?

I would guess places like Home Depot and Lowes will have little stick on feet. Heck you could even try stick on felt pads, something that would get the fan even closer to the unit than feet.